(19)
(11)EP 2 965 131 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
29.04.2020 Bulletin 2020/18

(21)Application number: 14708018.8

(22)Date of filing:  04.03.2014
(51)International Patent Classification (IPC): 
G02B 1/11(2015.01)
G02B 1/02(2006.01)
(86)International application number:
PCT/EP2014/054183
(87)International publication number:
WO 2014/135544 (12.09.2014 Gazette  2014/37)

(54)

SYNTHETIC DIAMOND OPTICAL ELEMENTS

OPTISCHES ELEMENT MIT SYNTHETISCHEM DIAMANT

ÉLÉMENTS OPTIQUES EN DIAMANT SYNTHÉTIQUE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 06.03.2013 US 201361773581 P
23.04.2013 GB 201307321

(43)Date of publication of application:
13.01.2016 Bulletin 2016/02

(73)Proprietor: Element Six Technologies Limited
Didcot, OX11 0QR (GB)

(72)Inventors:
  • TWITCHEN, Daniel
    Santa Clara, California 95054 (US)
  • BENNETT, Andrew Michael
    Didcot Oxfordshire OX11 0QR (GB)
  • ANOIKIN, Yevgeny Vasilievich
    Santa Clara, California 95054 (US)
  • DE WIT, Hendrikus Gerardus Maria
    NL-5431NT Cuijk (NL)

(74)Representative: Mitchell, Matthew Benedict David 
Element Six Limited Group Intellectual Property Global Innovation Centre Harwell Oxford
Didcot, Oxfordshire OX11 0QR
Didcot, Oxfordshire OX11 0QR (GB)


(56)References cited: : 
WO-A1-2011/103630
GB-A- 2 433 737
  
  • KARLSSON AND F NIKOLAJEFF M: "Diamond micro-optics: microlenses and antireflection structures surfaces for the infrared spectral region", OPTICS EXPRESS, OSA (OPTICAL SOCIETY OF AMERICA), WASHINGTON DC, (US), vol. 11, no. 5, 1 January 2003 (2003-01-01), pages 502-507, XP007922699, ISSN: 1094-4087 cited in the application
  • DOUGLAS S HOBBS: "Study of the Environmental and Optical Durability of AR Microstructures in Sapphire, ALON, and Diamond", PROCEEDINGS OF SPIE, SPIE, US, vol. 7302, 1 January 2009 (2009-01-01), pages 73020J-1, XP007922696, ISSN: 0277-786X, DOI: 10.1117/12.818335 cited in the application
  • CHRISTIAN DELACROIX ET AL: "Design, manufacturing, and performance analysis of mid-infrared achromatic half-wave plates with diamond subwavelength gratings", APPLIED OPTICS, vol. 51, no. 24, 20 August 2012 (2012-08-20), page 5897, XP055119395, ISSN: 0003-6935, DOI: 10.1364/AO.51.005897
  • KONONENKO T V ET AL: "Formation of antireflective surface structures on diamond films by laser patterning", APPLIED PHYSICS A: MATERIALS SCIENCE & PROCESSING, SPRINGER INTERNATIONAL, DE, vol. A68, 1 January 1999 (1999-01-01), pages 99-102, XP007922695, ISSN: 0947-8396 cited in the application
  • DENATALE J F ET AL: "Fabrication and characterization of diamond moth eye antireflective surfaces on Ge", JOURNAL OF APPLIED PHYSICS, AMERICAN INSTITUTE OF PHYSICS, 2 HUNTINGTON QUADRANGLE, MELVILLE, NY 11747, vol. 71, no. 3, 1 February 1982 (1982-02-01), pages 1388-1393, XP007922692, ISSN: 0021-8979 cited in the application
  • ANDREW M. BENNETT ET AL: "CVD diamond for high power laser applications", PROCEEDINGS OF SPIE, vol. 8603, 22 February 2013 (2013-02-22), page 860307, XP55119388, ISSN: 0277-786X, DOI: 10.1117/12.2004422
  
Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


Description

Field of Invention



[0001] The present invention relates to synthetic diamond optical elements and particularly to the provision of an alternative to synthetic diamond optical elements comprising thin film anti-reflective coatings. Particular embodiments relate to synthetic diamond optical elements having optical, thermal, and mechanical characteristics suitable for high power optical applications although synthetic diamond optical elements as described herein may be used in other applications where the provision of an antireflective coating is undesirable due to factors including mechanical robustness, chemical inertness, low absorbance, and high thermal conductivity.

Background of Invention



[0002] Standard thin film anti-reflective coatings on synthetic diamond optical elements have excellent performance in terms of minimising reflection, but are limited in high power optical systems due to the ease with which they are damaged. Due to high absorbance and/or poor thermal conductivity the anti-reflective coating tends to be the weak point in any synthetic diamond window resulting in a synthetic diamond window with a low laser induced damage threshold (LIDT). Furthermore, even if the absorption level of a thin film anti-reflective coating is relatively low, the thin film can still fail in high power density optical applications. For example, for a 20 kW laser system damage of thin film anti-reflective coatings is problematic and current thin film anti-reflective coating solutions are unlikely to be compatible with laser systems operating at 40 kW or more. Such high power laser systems are desirable for a number of applications including laser produced plasma (LPP) extreme ultraviolet (EUV) lithography systems to drive integrated circuit processing to smaller dimensions. Such extreme optical applications will require a synthetic diamond window capable of handling extreme power densities and this will require the combination of: (1) a synthetic diamond material with the required dimensions and desired bulk optical characteristics including low optical reflectance/absorption/scatter; and; (2) an anti-reflective surface finish capable of handling extreme power densities. Thin film anti-reflective coatings can also be problematic in terms of their mechanical integrity, e.g. if subjected to scratching or abrasion.

[0003] As an alternative to thin film anti-reflective coatings, it is known that anti-reflective surface patterns such as moth-eye structures can be formed directly in the surface of an optical window material in order to provide an anti-reflective surface finish without the requirement of a coating. While such anti-reflective surface patterns have been successfully fabricated in a range of optical window materials, the application of this technology to synthetic diamond windows has proved problematic. The anti-reflective performance of such surface finishes has been variable due to the difficulty in processing precisely defined surface patterns into diamond material because of the extreme hardness and low toughness of diamond material. Furthermore, the processing methods required to form anti-reflective surface structures in diamond material have resulted in significant surface and sub-surface crystal damage being incorporated into the diamond material. This surface and sub-surface damage in the synthetic diamond window causes a number of inter-related detrimental effects including: (1) a reduction in the laser induced damage threshold of the synthetic diamond window; (2) a reduction in the power at which the synthetic diamond window can operate; and (3) a reduction in the optical performance of the synthetic diamond window as a result of beam aberrations caused by the surface and sub-surface damage. As such it would be desirable to develop a process which forms precisely defined anti-reflective surface structure into a synthetic diamond window without introducing surface and sub-surface crystal damage so as to achieve a synthetic diamond window which has a low absorbance, a low reflectance, a high laser induced damage threshold, and high optical performance with minimal beam aberrations on transmission through the synthetic diamond window. In addition, it would be desirable to provide a process which is low cost, compatible with existing materials processing, and scalable over large areas.

[0004] In relation to the above, a number of prior art documents have disclosed techniques for fabricating anti-reflective surface structure into diamond window materials as discussed below. However, it is believed that none of the prior art techniques have achieved the combination of features as identified above.

[0005] In "Materials for Infrared Windows and Domes" [Daniel Harris, published by The International Society for Optical Engineering, 1999] it is disclosed at section 6.1.1 that a moth eye surface structure can be formed directly in diamond material to reduce reflection. Here it is disclosed that such a surface structure can be fabricated by first etching a reverse moth eye structure into silicon by lithographic techniques and then growing diamond material on the etched surface by chemical vapour deposition. The silicon is then dissolved to leave the diamond material with a moth eye structure. It is described that a multi-layer structure including an outer diamond layer with a flat outer surface has a reflectance of about 18% at a wavelength of 10 µm, the reflectance being dominated by single-surface reflectance from the front face of the outer diamond layer (15%). When the flat diamond outer surface is replaced by a moth eye structure, reflectance is reduced to 7% at a wavelength of 10 µm.

[0006] One problem with this approach is that the reflectance is still relatively high and this is due to the fact that precisely defined anti-reflective structures cannot easily be achieved in diamond material by the technique of etching a reverse moth eye structure into a substrate and then growing diamond material on the etched surface by chemical vapour deposition. Furthermore, growth of diamond material on patterned substrates can lead to an increase in crystal defects such as dislocations within the diamond material which adversely affect the optical properties of the diamond material. Yet a further weakness of this approach is that the final optical element will inevitably include early stage nucleation diamond which has reduced thermal conductance and increased optical absorbance.

[0007] US5334342 discloses a similar method of fabricating moth-eye surface structures in diamond material by patterning a reverse moth eye structure into a substrate, growing diamond material on the patterned substrate, and then removing the substrate to leave the diamond material with a moth eye surface structure.

[0008] J. F. DeNatale et al [Fabrication and characterization of diamond moth eye antireflective surfaces on Germanium, J. Appl. Phys. 71, 1388 (1992)] have disclosed a similar approach by patterning a germanium substrate with a surface relief (moth eye) structure and then overgrowing a thin diamond film on the patterned substrate such that the thin diamond film retains the underlying surface structure of the patterned substrate. It is described that the progressive gradation in the effective refractive index between air and the composite substrate has reduced Fresnel reflection losses to below 1%. This provides a means of overcoming the high refractive index and surface roughness considerations that often limit optical applications of polycrystalline diamond thin films. However, there is no disclosure of how to fabricate such moth-eye structures in free-standing diamond windows and although reflection losses have been reduced to below 1%, there is no disclosure of the laser induced damage threshold of the diamond material which will be sensitive to the quality of the diamond material. The quality of the diamond material in this instance will likely be poor as it is grown on a patterned germanium substrate.

[0009] T.V. Kononenko [Formation of antireflective surface structures on diamond films by laser patterning, Applied Physics A, January 1999, Volume 68, Issue 1, pp 99-102] discloses an alternative to the substrate patterning and diamond over-growth technique disclosed in the previously described prior art. This paper describes diamond surface microstructuring by a laser ablation technique. The optical transmission of the diamond films was found to increase from 70% to 80% at a wavelength of 10.6 µm by forming a microstructured surface by laser ablation.

[0010] Douglas Hobbs ["Study of the Environmental and Optical Durability of AR Microstructures in Sapphire, ALON, and Diamond", www.telaztec.com] has also reported the fabrication of moth eye anti-reflective surface microstructures directly in diamond material. It is reported that diamond windows with anti-reflective surface structures have been fabricated which have a transmittance of approximately 80% at a wavelength of 10 µm which compares with a value of approximately 70% for an untreated diamond window. These results appear similar to those reported by Kononenko using a laser ablation technique for patterning a diamond surface.

[0011] Hobbs also discloses that the anti-reflective microstructured diamond windows were tested for laser induced damage threshold using a pulsed CO2 laser operating at 9.56 µm with a 100 ns pulse length and a pulse repetition frequency of 4 Hz. It is indicated that results of the tests were variable and inconsistent due to the nature of the diamond material but that the damage thresholds measured were in a range 50 to 100 J/cm2, a level much higher than can be achieved with thin-film anti-reflective coatings.

[0012] Two key points may be noted from the Hobbs paper. First, the transmittance value of 80% is still rather low and this would indicate that the quality of the diamond material is relatively poor, the surface structures fabricated in the diamond windows are not precisely defined, or that significant surface or sub-surface damage has been introduced into the diamond crystal structure when forming anti-reflective surface micro-structures. Secondly, the paper does not indicate how the anti-reflective surface structures were fabricated in the diamond windows. Previously described methods of fabricating anti-reflective surface structures in diamond windows have involved either substrate patterning and diamond overgrowth or direct patterning via laser ablation. An alternative technique is to directly etch anti-reflective surface structures into diamond windows. For example, various publications from Uppsala University in Sweden have focussed on inductively coupled plasma etching of surface structures in diamond material including: M. Karlsson, K. Hjort, and F. Nikolajeff, "Transfer of continuous-relief diffractive structures into diamond by use of inductively coupled plasma dry etching", Optics Letters 26, 1752-1754 (2001); M. Karlsson, and F. Nikolajeff, "Fabrication and evaluation of a diamond diffractive fan-out element for high power lasers," Opt. Express 11, 191-198 (2003); and M. Karlsson, and F. Nikolajeff, "Diamond micro-optics: Microlenses and antireflection structured surfaces for the infrared spectral region," Opt. Express 11, 502-507 (2003).

[0013] The Uppsala group have indicated that diamond-based optics provide an attractive alternative for high-power laser optics due to their damage resistance, reduced thermal lensing, and transparency from the UV to the far-IR spectral regions. The Uppsala group have highlighted the need for better surface patterning for diamond-based optics and have proposed an inductively coupled plasma etching approach which involves patterning a resist layer on an optical-quality synthetic diamond using direct-write electron-beam lithography followed by dry etching in an inductively coupled plasma (ICP). The gases used for the diamond etching are O2 and Ar and a typical ICP etch recipe is disclosed as comprising: gas flows of 7 sccm (standard cubic centimeters per minute) of O2, and 8 sccm of Ar; a chamber pressure of 2.5 mTorr; an ICP power of 600 W; bias voltages varied between -100 and -180 V; and sample etch times of between 2 and 20 minutes.

[0014] It has been indicated that by correctly designing and fabricating sub-wavelength anti-reflective structures on both sides of a diamond window, it is possible to increase the transmission at a wavelength of 10.6 µm from 71% (unstructured diamond) to almost 97% (for microstructured diamond). It is indicated that this improvement in transmission is very important for high-power lasers, in which even a fraction of the scattered high optical power can lead to severe problems. Applications of this technology are described as including outcoupling windows for neodymium-doped yttrium aluminum garnet (Nd:YAG) or CO2 lasers, satellite windows, and in x-ray optics. It is indicated that in these applications, it is mainly the high thermal conductivity, the high laser damage threshold, and the high wear resistance of the optical windows that are the driving factors.

[0015] GB2433737 describes diamond material with a high laser induced damage threshold and low absorption coefficient but this material does not have an anti-reflective surface pattern formed directly on a surface.

[0016] Despite the above progress in fabricating anti-reflective surface structures into diamond windows, there is still a need to provide improved anti-reflective surface structures. It would be desirable to develop a process which forms precisely defined anti-reflective surface structure into a synthetic diamond window without introducing surface and sub-surface crystal damage so as to achieve a synthetic diamond window which has a low reflectance, a high laser induced damage threshold, and high optical performance with minimal beam aberrations on transmission through the synthetic diamond window. In this regard, while a number of prior art documents have disclosed techniques for fabricating anti-reflective surface structure into diamond window material as previously discussed, it is believed that none of the prior art techniques have achieved this desired combination of features. Furthermore, it has also been noted that a direct-write electron-beam lithography process for patterning of the resist prior to etching is time consuming and expensive.

[0017] In light of the above, it is an aim of embodiments of the present invention to provide a synthetic diamond optical element comprising an anti-reflective surface pattern formed directly in the surface of the synthetic diamond material and which has low absorbance and low reflectance while also having low surface and sub-surface crystal damage thus exhibiting a high laser induced damage threshold. It is a further aim to develop a technique for fabricating such anti-reflective surface patterns in diamond material which is relatively quick and low cost.

Summary of Invention



[0018] According to a first aspect of the present invention there is provided an optical element comprising:

synthetic diamond material; and

an anti-reflective surface pattern formed directly in at least one surface of the synthetic diamond material,

wherein the optical element has an absorption coefficient measured at room temperature of ≤ 0.5 cm-1 at a wavelength of 10.6 µm,

wherein the optical element has a reflectance at said at least one surface of no more than 2% at an operating wavelength of the optical element, and

wherein the optical element has a laser induced damage threshold meeting one or both of the following characteristics:

the laser induced damage threshold is at least 30 Jcm-2 measured using a pulsed laser at a wavelength of 10.6 µm with a pulse duration of 100 ns and a pulse repetition frequency in a range 1 to 10 Hz; and

the laser induced damage threshold is at least 1 MW/cm2 measured using a continuous wave laser at a wavelength of 10.6 µm.



[0019] According to a second aspect of the present invention there is provided an optical system comprising:

an optical element as defined above; and

a light source configured to generate light at a power of at least 20 kW and transmit said light through the optical element.


Brief Description of the Drawings



[0020] For a better understanding of the present invention and to show how the same may be carried into effect, embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows a schematic flow diagram of a method of fabricating an optical element comprising synthetic diamond material with an anti-reflective surface finish pattern formed directly in a surface of the synthetic diamond material; and

Figure 2 shows a schematic diagram of a high power laser system comprising a high power laser source and an optical element formed of synthetic diamond material with an anti-reflective surface pattern formed directly in a surface of the synthetic diamond material.


Detailed Description



[0021] The present inventors have realized that recent developments in processing of high purity single crystal CVD diamond materials in the field of quantum sensing and quantum information processing can be transferred to the field of high power polycrystalline CVD diamond laser optics to solve the problems outlined in the background section of this specification and achieve the fabrication of synthetic diamond optical elements which have low reflectance and high transmittance while also having low surface and sub-surface crystal damage thus exhibiting a high laser induced damage threshold.

[0022] Research into the use of high purity single crystal CVD diamond materials in the field of quantum sensing and quantum information processing is focussed on a particularly kind of point defect found within the diamond crystal lattice, namely the negatively changed nitrogen-vacancy defect (NV-). The NV- defect has an electronic spin which can be manipulated to function as a quantum bit or alternatively as a quantum sensing element. The NV- defect can be optically excited, manipulated using microwaves, and emits fluorescent light which is characteristic of its electronic spin state.

[0023] One requirement for quantum sensing and quantum information processing applications is that the NV- electronic spin defect should have a long quantum coherence time and this requires the NV- electronic spin defect to be located in a highly pure diamond lattice environment which has a low concentration of crystal defects and low internal stress which can otherwise detrimentally reduce the quantum coherence time of the NV- electronic spin defects disposed within the diamond crystal lattice. Another requirement for quantum sensing and quantum information processing applications is that the fluorescent light emitted from the NV- electronic spin defects needs to be efficiently out-coupled from the diamond material to a suitable processor or detector configuration and in this regard it is desirable to fabricate nanowires, optical waveguide structures, and photonic cavity structures into the diamond material in order to effectively out-couple photons emitted from the NV- electronic spin defects. Inductively coupled plasma etching (similar to that used by Uppsala University and discussed previously in the background section of this specification) has been used to fabricate such optical structures. However, it has been found that fabrication processes tend to introduce surface and sub-surface damage into the diamond crystal structure which adversely effects the quantum coherence time of the near-surface NV- electronic spin defects coupled to the optical surface structures. Furthermore, it has been found that the quality of the desired surface structures and the formation of unwanted etch grass between the desired surface structures is sensitive to the type of etch mask used and to the etch conditions. As such, recent work by groups developing structures for diamond quantum devices has focussed on refining the inductively coupled plasma (ICP) etching process in order to allow fabrication of optical out-coupling structures for near-surface NV- electronic spin defects without introducing significant quantities of surface and sub-surface damage into the diamond crystal structure while at the same time achieving well defined optical structures in the diamond surface without unwanted etch grass disposed between the structures. This work is described in a number of publications including: B. Hausmann et al, Fabrication of diamond nanowires for quantum information processing applications, Diamond and Related Materials 19, 621-629 (2010); M. Burek et al., Free-standing mechanical and photonic nanostructures in single crystal diamond, Nano Lett. 2012; and US2001/0309265.

[0024] Groups developing structures for diamond quantum devices have experimented with a variety of different combinations of gas flow rates, ICP powers, and pressures for fabricating optical out-coupling structures in single crystal CVD diamond material without introducing significant quantities of surface and sub-surface damage into the diamond crystal structure. For example, the following inductively coupled plasma reactive ion etching (ICP RIE) recipe is reported in the literature as being suitable for this purpose: an oxygen etchant which has an oxygen gas flow of between 30 to 50 sccm O2, a chamber pressure of approximately 10 mTorr, and an ICP power of approximately 700 W. It is reported that this etch recipe allows the formation of very well defined surface structures while avoiding the formation of etch grass between the desired surface structures. In addition, it is reported that the shape and quantity of the etched optical structures in a diamond surface can be controlled by varying the ICP power during the etching process. For example, in the fabrication of nano-wires in the surface of single crystal CVD diamond material a multi-step ICP RIE process is reported including applying an ICP power of 700 W for two minutes, an ICP power of 600 W for three minutes, and an ICP power of 1000 W for five minutes. Further still, a number of different etch masks are reported in the diamond quantum device literature including Al2O3 particles, Au particles, SiO2 particles, evaporated Au, and FOx e-beam resist.

[0025] In light of the above, it is evident that groups developing structures for diamond quantum devices based on defects in the diamond lattice have successfully developed an ICP RIE process which is capable of forming well defined surface structures in diamond material without forming unwanted etch grass between such structures and without introducing a large amount of surface and sub-surface crystal damage. This technology has been developed specifically for efficiently out-coupling fluorescent light emitted from the NV- electronic spin defects in quantum sensing and quantum information processing applications including the formation of nanowires, optical waveguide structures, and photonic cavity structures into the diamond material in order to effectively out-couple photons emitted from the NV- electronic spin defects.

[0026] The present inventors have realized that the requirements for out-coupling structures such as nanowires, optical waveguide structures, and photonic cavity structures in quantum sensing and quantum information processing applications are very similar to the requirements for the fabrication of better anti-reflective surface patterns in transmissive diamond windows suitable for high power laser applications. That is, the etching technology developed for quantum sensing and quantum information processing applications can be transferred into the field of transmissive optics to provide a synthetic diamond window for high power laser applications comprising an anti-reflective surface pattern, such as a moth-eye pattern, formed directly in the surface of the synthetic diamond window and which has low reflectance and high transmittance while also having low surface and sub-surface crystal damage thus exhibiting a high laser induced damage threshold. While the etching technology developed for quantum sensing and quantum information processing applications is utilized for etching nanowires, optical waveguide structures, and photonic cavity structures in single crystal CVD diamond material comprising fluorescent NV- defects, in accordance with embodiments of the present invention the etching technology is applied to low absorbance optical quality diamond material, such as high quality polycrystalline CVD diamond material, to fabricate low surface damage anti-reflective surface finishes, such as moth-eye structures, therein and thus produce optical elements having a combination of low absorbance, low reflectance, and a high laser induced damage threshold.

[0027] A method of fabricating an optical element is provided as illustrated in Figure 1 which comprises:

forming a patterned resist layer 2 on at least one surface of a synthetic diamond material 4;

etching 3 the at least one surface of the synthetic diamond material 4 through the patterned resist layer 2; and

removing the patterned resist layer to leave an anti-reflective surface pattern 6 formed directly in the at least one surface of the synthetic diamond material 4,

wherein the etching comprises, for example, an inductively coupled plasma reactive ion etching (ICP RIE) process comprising an oxygen gas flow rate of between 20 to 50 sccm O2, a chamber pressure of between 5 and 20 mTorr, and an ICP power of between 600 and 1100 W.



[0028] Optionally, the inductively coupled plasma reactive ion etching process comprises one or more of: an oxygen flow rate between 25 and 35 sccm O2; a chamber pressure between 7 and 15 mTorr; and an ICP power between 700 and 1000 W. The inductively coupled plasma reactive ion etching process may also comprise multiple steps with different ICP powers to control the surface profile of the anti-reflective surface pattern. Furthermore, the patterned resist layer may be formed from one of: Al2O3 particles; Au particles; SiO2 particles; evaporated Au; and FOx e-beam resist. In practice, the resist is selected to be tolerant to a controlled deep etch. For example, a resist may be selected to be compatible with the formation of surface etch features having a height equal to or greater than 2 µm, 4 um, 6 µm, 8 µm, or 10 µm.

[0029] In addition to the above, it has been note that certain prior art approaches as described in the background section utilize a direct-write electron-beam lithography process for patterning of the resist prior to etching. This direct-write electron-beam lithography process can be somewhat time consuming and expensive. As such, according to one alternative option which may provide a faster and more cost effective route to patterning the resist layer, it is proposed that the patterned resist layer is formed using an interference lithography technique. Interference lithography techniques are already known in the art for forming moth eye antireflective structures in other materials. For example, Telaztec™ utilize this approach for fabricating moth eye antireflective structures in a range of materials. It is proposed here that such an interference lithography technique for patterning the resist may be combined with a low surface/sub-surface crystal damage etching technology as a route to providing a commercially viable way of fabricating diamond optical windows with low absorbance, low reflectance, and a high laser induced damage threshold for high power laser applications.

[0030] Applying the aforementioned methodology, one aspect of the present invention is an optical element comprising:

synthetic diamond material; and

an anti-reflective surface pattern formed directly in at least one surface of the synthetic diamond material,

wherein the optical element has an absorption coefficient measured at room temperature of ≤ 0.5 cm-1, ≤ 0.4 cm-1, ≤ 0.3 cm-1, ≤ 0.2 cm-1, ≤ 0.1 cm-1, ≤ 0.07 cm-1 or ≤ 0.05 cm-1 at a wavelength of 10.6 µm,

wherein the optical element has a reflectance at said at least one surface of no more than 2%, 1.5%, 1%, or 0.5% at an operating wavelength of the optical element, and

wherein the optical element has a laser induced damage threshold meeting one or both of the following characteristics:

the laser induced damage threshold is at least 30 Jcm-2, 50 Jcm-2, 75 Jcm-2, 100 Jcm-2, 150 Jcm-2, or 200 Jcm-2 measured using a pulsed laser at a wavelength of 10.6 µm with a pulse duration of 100 ns and a pulse repetition frequency in a range 1 to 10 Hz; and

the laser induced damage threshold is at least 1 MW/cm2, 5 MW/cm2, 10 MW/cm2, 20 MW/cm2, or 50 MW/cm2 measured using a continuous wave laser at a wavelength of 10.6 µm.



[0031] Absorbance, reflectance, and laser induced damage threshold of an optical element are readily measurable by those skilled in the art (for example, ISO 21254-2:2011 describes methods for measuring laser induced damage threshold while Sussmann et al. [Diamond and Related Materials, 3, 1173-117, 1994] describe the specific application of laser damage testing to CVD diamond windows).

[0032] It should be noted that reflectance for an optical element will be dependent on the operating wavelength and that the anti-reflective surface pattern will be designed to be optimized for a particular operating wavelength. It is known in the art how to optimize the design of an anti-reflective surface pattern for a particular operating wavelength. What is considered to be new here is the ability to provide the combination of low absorbance, low surface reflectance, and high laser induced damage threshold in a synthetic diamond material. Where the operating wavelength for an optical element is unknown, then a range of wavelengths can be tested to determine where reflectance is minimized and this will correspond to the operating wavelength for the purposes of the present specification. That said, optionally the operating wavelength is selected from one of: 10.6 µm; 1.06 µm; 532 nm; 355 nm; or 266 nm, with an operating wavelength of 10.6 µm being preferred for certain commercial applications.

[0033] A synthetic diamond optical element is provided which has low absorbance and low reflectance in combination with low surface damage and an increased laser induced damage threshold. This is considered to be a key combination of parameters for high power laser windows and other high power laser optics such as prisms and lenses. As such, the present invention is considered to be an enabling technology for high power laser systems. Furthermore, the present invention can be used in applications where the synthetic diamond optical element may be subjected to scratching or abrasion, e.g. in watch glass applications, by avoiding the requirement for a thin film coating on the synthetic diamond material which can be readily damaged.

[0034] Optionally, the optical element may also have one or more of the following characteristics:

a transmittance of at least 97%, 98% or 99% at the operating frequency of the optical element.;

a total integrated scatter in a forward hemisphere no more than 2%, 1%, 0.5%, or 0.1% at the operating frequency of the optical element;

a dielectric loss coefficient tan δ measured at room temperature at 145 GHz of ≤ 2 x 10-4, ≤ 10-4, ≤ 5 x 10-5 ≤ 10-5, ≤ 5 x 10-6, or ≤ 10-6;

an average black spot density no greater than 5 mm-2, 3 mm-2, 1 mm-2, 0.5 mm-2, or 0.1 mm-2;

a black spot distribution such that there are no more than 5, 4, 3, 2, or 1 black spots within any 3 mm2 area;

an integrated absorbance per unit thickness of no more than 0.20 cm-2, 0.15 cm-2, 0.10 cm-2, or 0.05 cm-2, when measured with a corrected linear background in a range 2760 cm-1 to 3030 cm-1;

a thermal conductivity of no less than 1800 Wm-1K-1, 1900 Wm-1K-1, 2000 Wm-1K-1, 2100 Wm-1K-1, or 2200 Wm-1K-1;

a silicon concentration as measured by secondary ion mass spectrometry of no more than 1017 cm-3 5 x 1016 cm-3 , 1016 cm-3 5 x 1015 cm-3 , or 1015 cm-3 ; and

an oxygen terminated surface.



[0035] Such optical characteristics can be achieved by applying the patterning technology as described herein to high quality optical grades of synthetic diamond material, such as high quality optical grade polycrystalline CVD diamond available from Element Six Limited. It is also envisaged that the patterning technology may be applied to optical grade single crystal CVD diamond (also available from Element Six Limited) for certain optical applications. Advantageously, the optical element meets one or more of the optical characteristics as described herein over at least 50%, 60%, 70%, 80%, 90%, or 100% of the area of the surface of the diamond optical element on which the anti-reflective diffractive surface finish is formed. In this regard, diamond optical elements can be fabricated to relatively large areas. For example, synthetic diamond components can be fabricated to a have largest linear dimension of at least 10 mm, 20 mm, 40 mm, 60 mm, 80 mm, 100 mm, 120 mm, or 140 mm. Such synthetic diamond components may be fabricated with a thickness equal to or greater than 200 µm, 250 µm, 350 µm, 450 µm, 500 µm, 750 µm, 1000 µm, 1500 µm, or 2000 µm.

[0036] Advantageously, the synthetic diamond material is fabricated by growing to a target thickness greater than that required for the final optical element and then processing a nucleation face of the diamond material to remove early stage nucleation diamond. As indicated in the background section, one weakness of prior art approaches is that early stage nucleation diamond is incorporated into the final optical element leading to a reduction in thermal conductance and an increase in optical absorbance. By growing the synthetic diamond material to a target thickness greater than that required for the final optical element it is possible to remove early stage nucleation diamond and thus provide an optical element with higher thermal conductance and lower optical absorbance. Removal of early stage nucleation diamond will inevitably result in a slight reduction in the strength of the synthetic diamond material. However, manufacturers such as Element Six Limited are capable of fabricating thick wafers of synthetic diamond material, such as polycrystalline CVD diamond wafers, with a high tensile rupture strength which enables removal of early stage nucleation diamond while retaining sufficient mechanical strength for end applications. For example, the synthetic diamond material may have one or more of the following structural characteristics:

a tensile rupture strength with a nucleation face of the synthetic diamond material in tension of: ≥ 760 MPa x n for a thickness of 200 to 500 µm; ≥ 700 MPa x n for a thickness of 500 to 750 µm; ≥ 650 MPa x n for a thickness of 750 to 1000 µm; ≥ 600 MPa x n for a thickness of 1000 to 1250 µm; ≥ 550 MPa x n for a thickness of 1250 to 1500 µm; ≥ 500 MPa x n for a thickness of 1500 to 1750 µm; ≥ 450 MPa x n for a thickness of 1750 to 2000 µm; or ≥ 400 MPa x n for a thickness of ≥ 2000 µm, wherein multiplying factor n is 1.0, 1.1, 1.2, 1.4, 1.6, 1.8, or 2; and

a tensile rupture strength with a growth face of the synthetic diamond material in tension of: ≥ 330 MPa x n for a thickness of 200 to 500 µm; ≥ 300 MPa x n for a thickness of 500 to 750 µm; ≥ 275 MPa x n for a thickness of 750 to 1000 µm; ≥ 250 MPa x n for a thickness of 1000 to 1250 µm; ≥ 225 MPa x n for a thickness of 1250 to 1500 µm; ≥ 200 MPa x n for a thickness of 1500 to 1750 µm; ≥ 175 MPa x n for a thickness of 1750 to 2000 µm; or ≥ 150 MPa x n for a thickness of ≥ 2000 µm, wherein multiplying factor n is 1.0 1.1, 1.2, 1.4, 1.6, 1.8, or 2.



[0037] Such synthetic diamond material may be processed to a surface flatness ≤ 5 µm, ≤ 4 µm, ≤ 3 µm, ≤ 2 µm, ≤ 1 µm, ≤ 0.5 µm, ≤ 0.2 µm, ≤ or 0.1 µm and/or a surface roughness Ra no more than 200 nm, 150 nm, 100 nm, 80 nm, 60 nm, 40 nm, 20 nm, or 10 nm.

[0038] Further improvements to the thermal conductivity of the synthetic diamond material can be made by reducing the natural 1.1% 13C content of the material. As such, the synthetic diamond material may comprise at least a portion which has a 13C content of less than 1.0%, 0.8%, 0.6%, 0.4%, 0.2%, 0.1%, 0.05%, or 0.01%. In this regard, it should be noted that isotopically purified carbon source gas is expensive. As such, rather than fabricate the entire optical element from isotopically purified diamond material it can be advantageous to only fabricate a portion of the optical element from isotopically purified diamond material. For example, one or more surface layers of the synthetic diamond material may be formed of isotopically purified diamond material with the interior bulk being fabricated using a higher 13C content, preferable natural abundance. In one particularly useful embodiment a surface layer comprising the anti-reflective surface pattern is formed of isotopically purified diamond material so as to increase the thermal conductivity of the anti-reflective surface pattern and thus reduce localized heating and increase the laser induced damage threshold of the anti-reflective surface pattern. An underlying portion of synthetic diamond material may then comprise a higher concentration of 13C, preferably natural abundance, to reduce synthesis costs.

[0039] The anti-reflective surface finish of the present invention may be formed over the majority of a surface of the synthetic diamond material, e.g. over at least 50%, 60%, 70%, 80%, 90%, or over the entire surface. As such, the anti-reflective diffractive surface finish can be formed over an area of at least 50 mm2, 100 mm2, 200 mm2, 300 mm2, 500 mm2, 700 mm2, 1000 mm2, 1500 mm2, 2000 mm2, 3000 mm2, 5000 mm2, 7000 mm2, 10000 mm2, 15000 mm2, or 20000 mm2.

[0040] The surface which is patterned with the anti-reflective surface finish may, for example, form the major optical exit and/or entry face of a diamond window, lens or prism with a majority, or the entire, optical exit and/or entry face of the optical element being patterned with an anti-reflective diffractive surface finish. In some applications it may be desirable to leave an unpatterned portion around a peripheral region of the transmissive optical element for mounting the transmissive optical element. Optionally, the anti-reflective surface pattern is formed on at least two surfaces of the synthetic diamond material. For example, the anti-reflective diffractive surface finish can be formed on both the optical entry face and the optical exit face of the optical element, e.g. on opposing major faces of a diamond window. Alternatively, for certain optical elements low reflectance is only required on one surface of the optical element, e.g. a beam splitter where partial reflectance is required on one surface.

[0041] Optical elements fabricated from high quality optical grade synthetic diamond material and comprising an anti-reflective surface pattern as described herein are suitable for use in high power optical systems due to their low reflectance and high laser induced damage threshold. As such, according to another aspect of the present invention there is provided an optical system as illustrated in Figure 2 comprising:

a synthetic diamond optical element 10 comprising an anti-reflective surface pattern as described herein; and

a light source 12 (e.g. a laser) configured to generate light 14 at a power of at least 20 kW, 25 kW, 30 kW, 35 kW, 40 kW, 45 kW, or 50 kW and transmit said light through the synthetic diamond optical element 10.



[0042] In relation to the above, it will be noted that the operating power of the described optical system is significantly lower that the previously defined continuous wave laser induced damage threshold of 1 MW/cm2. However, it should be noted that to provide an optical element that has a long operating lifetime the laser induced damage threshold of the synthetic diamond optical element should be significantly higher than the operating power of the optical system.

[0043] In the illustrated embodiment of Figure 2 the optical element 10 is in the form of a transmissive diamond window with an anti-reflective surface pattern 16 fabricated in both major faces of the window. It should be noted that while the anti-reflective surface pattern illustrated in Figures 1 and 2 has a rectangular form this is for illustrative purposes only. The etching technology as described herein is capable of generating a range of cross-sectional shapes and thus is it possible to tailor the profile of the anti-reflective surface structure in order to optimize transmission, reflection, and laser induced damage threshold parameters for a particular application requirement.

[0044] Optionally, the aforementioned optical system may also provide a cooling system for cooling the synthetic diamond optical element. In this regard, the present inventors have noted that Element Six's optical grade synthetic diamond material shows a large decrease in absorption at low temperatures. This effect is not seen to the same extent with certain other diamond materials.

[0045] In summary, it is believed that optical elements as described herein comprise the key combination of parameters for high power laser windows. As such, the present invention is considered to be an enabling technology for high power laser systems. Furthermore, it is also envisaged that optical elements as described herein may be used in broad band visible wavelength applications (e.g. watch faces) where anti-reflective surface finishes may be provided for their mechanical robustness relative to thin film coatings.

[0046] While this invention has been particularly shown and described with reference to preferred embodiments, it will be understood to those skilled in the art that various changes in form and detail may be made without departing from the scope of the invention as defined by the appendant claims.


Claims

1. An optical element comprising:

synthetic diamond material; and

an anti-reflective surface pattern formed directly in at least one surface of the synthetic diamond material,

wherein the optical element has an absorption coefficient measured at room temperature of ≤ 0.5 cm-1 at a wavelength of 10.6 µm,

wherein the optical element has a reflectance at said at least one surface of no more than 2% at an operating wavelength of the optical element, and

wherein the optical element has a laser induced damage threshold meeting one or both of the following characteristics:

the laser induced damage threshold is at least 30 Jcm-2 measured using a pulsed laser at a wavelength of 10.6 µm with a pulse duration of 100 ns and a pulse repetition frequency in a range 1 to 10 Hz; and

the laser induced damage threshold is at least 1 MW/cm2 measured using a continuous wave laser at a wavelength of 10.6 µm.


 
2. An optical element according to claim 1,
wherein the operating wavelength is selected from one of: 10.6 µm; 1.06 µm; 532 nm; 355 nm; or 266 nm.
 
3. An optical element according to any preceding claim,
wherein the laser induced damage threshold is at least 50 Jcm-2, 75 Jcm-2, 100 Jcm-2, 150 Jcm-2, or 200 Jcm-2 measured using said pulsed laser.
 
4. An optical element according to any preceding claim,
wherein the laser induced damage threshold is at least 5 MW/cm2, 10 MW/cm2, 20 MW/cm2, or 50 MW/cm2 measured using said continuous wave laser.
 
5. An optical element according to any preceding claim,
wherein the reflectance at said at least one surface is no more than 1.5%, 1%, or 0.5% at the operating wavelength of the optical element.
 
6. An optical element according to any preceding claim,
wherein the optical element has a transmittance of at least 97%, 98% or 99% at the operating wavelength of the optical element.
 
7. An optical element according to any preceding claim,
wherein the optical element has a total integrated scatter in a forward hemisphere no more than 2%, 1%, 0.5%, or 0.1% at the operating wavelength of the optical element.
 
8. An optical element according to any preceding claim,
wherein the optical element has an absorption coefficient measured at room temperature of ≤ 0.4 cm-1, ≤ 0.3 cm-1, ≤ 0.2 cm-1, ≤ 0.1 cm-1, ≤ 0.07 cm-1 or ≤ 0.05 cm-1 at 10.6 µm.
 
9. An optical element according to any preceding claim,
wherein the optical element has a dielectric loss coefficient tan δ measured at room temperature at 145 GHz of ≤ 2 x 10-4, ≤ 10-4, ≤ 5 x 10-5, ≤ 10-5, ≤ 5 x 10-6, or ≤ 10-6.
 
10. An optical element according to any preceding claim,
wherein the optical element has one or more of the following characteristics:

an average black spot density no greater than 5 mm-2, 3 mm-2, 1 mm-2, 0.5 mm-2, or 0.1 mm-2;

a black spot distribution such that there are no more than 5, 4, 3, 2, or 1 black spots within any 3 mm2 area;

an integrated absorbance per unit thickness of no more than 0.20 cm-2, 0.15 cm-2, 0.10 cm-2, or 0.05 cm-2, when measured with a corrected linear background in a range 2760 cm-1 to 3030 cm-1;

a thermal conductivity of no less than 1800 Wm-1K-1, 1900 Wm-1K-1, 2000 Wm-1K-1, 2100 Wm-1K-1, or 2200 Wm-1K-1; and

a silicon concentration as measured by secondary ion mass spectrometry of no more than 1017 cm-3, 5 x 1016 cm-3, 1016 cm-3, 5 x 1015 cm-3, or 1015 cm-3.


 
11. An optical element according to any preceding claim,
wherein the anti-reflective surface pattern is formed in at least one surface of the synthetic diamond material over an area of at least 50 mm2, 100 mm2, 200 mm2, 300 mm2, 500 mm2, 700 mm2, 1000 mm2, 1500 mm2, 2000 mm2, 3000 mm2, 5000 mm2, 7000 mm2, 10000 mm2, 15000 mm2, or 20000 mm2.
 
12. An optical element according to claim 11,
wherein the optical element meets the requirements defined in one or more of claims 1 to 10 over at least 50%, 60%, 70%, 80%, 90%, or 100% of said area.
 
13. An optical system comprising:

an optical element according to any preceding claim; and

a light source configured to generate light at a power of at least 20 kW and transmit said light through the optical element.


 
14. An optical system according to claim 13,
wherein the light source is configured to generate light at a power of at least 25 kW, 30 kW, 35 kW, 40 kW, 45 kW, or 50 kW.
 
15. An optical system according to claim 13 or 14, further comprising a cooling system for cooling the optical element.
 


Ansprüche

1. Optisches Element, das
synthetisches Diamantmaterial, und
ein antireflektierendes Oberflächenmuster umfasst, das direkt in mindestens einer Oberfläche des synthetischen Diamantmaterials gebildet ist,
wobei das optische Element einen bei Raumtemperatur gemessenen Absorptionskoeffizienten von ≤ 0,5 cm-1 bei einer Wellenlänge von 10,6 µm aufweist,
wobei das optische Element einen Reflexionsgrad auf der mindestens einen Oberfläche von nicht mehr als 2 % bei einer Arbeitswellenlänge des optischen Elements aufweist, und wobei das optische Element eine Laser-induzierte Schadensschwelle aufweist, die ein oder beide der folgenden Charakteristika erfüllt:

die Laser-induzierte Schadensschwelle beträgt mindestens 30 Jcm-2, gemessen unter Verwendung eines gepulsten Lasers bei einer Wellenlänge von 10,6 µm mit einer Pulsdauer von 100 ns und einer Pulswiederholungsfrequenz in einem Bereich von 1 bis 10 Hz, und

die Laser-induzierte Schadensschwelle beträgt mindestens 1 MW/cm2, gemessen unter Verwendung eines Dauerstrichlasers bei einer Wellenlänge von 10,6 µm.


 
2. Optisches Element nach Anspruch 1,
bei dem die Arbeitswellenlänge ausgewählt ist aus einer von: 10,6 µm, 1,06 µm, 532 nm, 355 nm oder 266 nm.
 
3. Optisches Element nach einem der vorhergehenden Ansprüche, bei dem die Laser-induzierte Schadensschwelle mindestens 50 Jcm-2, 75 Jcm-2, 100 Jcm-2, 150 Jcm-2 oder 200 Jcm-2 beträgt, gemessen unter Verwendung des gepulsten Lasers.
 
4. Optisches Element nach einem der vorhergehenden Ansprüche, bei dem die Laser-induzierte Schadensschwelle mindestens 5 MW/cm2, 10 MW/cm2, 20 MW/cm2 oder 50 MW/cm2 beträgt, gemessen unter Verwendung des Dauerstrichlasers.
 
5. Optisches Element nach einem der vorhergehenden Ansprüche, bei dem der Reflexionsgrad an der mindestens einen Oberfläche nicht mehr als 1,5 %, 1 % oder 0,5 % bei der Arbeitswellenlänge des optischen Elements beträgt.
 
6. Optisches Element nach einem der vorhergehenden Ansprüche, das einen Transmissionsgrad von mindestens 97 %, 98 % oder 99 % bei der Arbeitswellenlänge des optischen Elements aufweist.
 
7. Optisches Element nach einem der vorhergehenden Ansprüche, das eine gesamte integrierte Streuung in einen vorderen Halbraum von nicht mehr als 2 %, 1 %, 0,5 % oder 0,1 % bei der Arbeitswellenlänge des optischen Elements aufweist.
 
8. Optisches Element nach einem der vorhergehenden Ansprüche, das einen bei Raumtemperatur gemessenen Absorptionskoeffizienten von 0,4 cm1, ≤ 0,3 cm-1, ≤ 0,2 cm-1, ≤ 0,1 cm-1, ≤ 0,07 cm-1 oder ≤ 0,05 cm-1 bei 10,6 µm aufweist.
 
9. Optisches Element nach einem der vorhergehenden Ansprüche, das einen bei Raumtemperatur gemessenen dielektrischen Verlustkoeffizienten tan δ bei 145 GHz von ≤ 2 x 10-4, ≤ 10-4, ≤ 5 x 10-5, ≤ 10-5, ≤ 5 x 10-6 oder ≤ 10-6 aufweist.
 
10. Optisches Element nach einem der vorhergehenden Ansprüche, das ein oder mehrere der folgenden Charakteristika aufweist:

eine durchschnittliche Schwarzpunktdichte von nicht mehr als 5 mm-2, 3 mm-2, 1 mm-2, 0, 5 mm-2 oder 0,1 mm-2,

eine Schwarzpunktverteilung, so dass sich innerhalb eines beliebigen Flächeninhalts von 3 mm2 nicht mehr als 5, 4, 3, 2 oder 1 Schwarzpunkte befinden,

einen integrierten Absorptionsgrad pro Dickeneinheit von nicht mehr als 0,20 cm-2, 0,15 cm-2, 0,10 cm-2 oder 0,05 cm-2, gemessen gegen einen korrigierten linearen Hintergrund in einem Bereich von 2760 cm-1 bis 3030 cm-1,

eine Wärmeleitfähigkeit von nicht weniger als 1800 Wm-1K-1, 1900 Wm-1K-1, 2000 Wm-1K-1, 2100 Wm-1K-1 oder 2200 Wm-1K-1 und eine durch Sekundärionenmassenspektrometrie gemessene Siliciumkonzentration von nicht mehr als 1017 cm-3, 5 x 1016 cm-3, 1016 cm-3, 5 x 1015 cm-3 oder 1015 cm-3.


 
11. Optisches Element nach einem der vorhergehenden Ansprüche,
bei dem das antireflektierende Oberflächenmuster in mindestens einer Oberfläche des synthetischen Diamantmaterials über einen Flächeninhalt von mindestens 50 mm2, 100 mm2, 200 mm2, 300 mm2, 500 mm2, 700 mm2, 1000 mm2, 1500 mm2, 2000 mm2, 3000 mm2, 5000 mm2, 7000 mm2, 10000 mm2, 15000 mm2 oder 20000 mm2 gebildet ist.
 
12. Optisches Element nach Anspruch 11,
das die in einem oder mehreren der Ansprüche 1 bis 10 definierten Anforderungen über mindestens 50 %, 60 %, 70 %, 80 %, 90 % oder 100 % seines Flächeninhalts erfüllt.
 
13. Optisches Element, das
ein optisches Element nach einem der vorhergehenden Ansprüche, und
eine Lichtquelle umfasst, die ausgestaltet ist, um Licht mit einer Leistung von mindestens 20 kW zu erzeugen und das Licht durch das optische Element hindurch zu übertragen.
 
14. Optisches System nach Anspruch 13,
bei dem die Lichtquelle ausgestaltet ist, um Licht mit einer Leistung von mindestens 25 kW, 30 kW, 35 kW, 40 kW, 45 kW oder 50 kW zu erzeugen.
 
15. Optisches System nach Anspruch 13 oder 14, das des Weiteren ein Kühlsystem zum Kühlen des optischen Elements umfasst.
 


Revendications

1. Elément optique, comprenant :

un matériau en diamant synthétique ; et

un motif de surface anti-réfléchissant formé directement dans au moins une surface du matériau en diamant synthétique,

dans lequel l'élément optique a un coefficient d'absorption, mesuré à la température ambiante, ≤ 0,5 cm-1 à une longueur d'onde de 10,6 µm,

dans lequel l'élément optique a un facteur de réflexion, au niveau de ladite au moins une surface, qui n'est pas supérieur à 2% à une longueur d'onde de fonctionnement de l'élément optique, et

dans lequel l'élément optique a un seuil de détérioration induit par laser satisfaisant à l'une ou aux deux des caractéristiques suivantes :

le seuil de détérioration induit par laser est d'au moins 30 Jcm-2, mesuré à l'aide d'un laser pulsé à une longueur d'onde de 10,6 µm avec une durée des impulsions de 100 ns et une fréquence de répétition d'impulsion située dans une plage comprise entre 1 et 10 Hz ; et

le seuil de détérioration induit par laser est d'au moins 1 MW/cm2, mesuré à l'aide d'un laser à onde continue à une longueur d'onde de 10,6 µm.


 
2. Elément optique selon la revendication 1,
dans lequel la longueur d'onde de fonctionnement est sélectionnée parmi l'une de : 10,6 µm ; 1,06 µm ; 532 nm ; 355 nm ; ou 266 nm.
 
3. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel le seuil de détérioration induit par laser est d'au moins 50 Jcm-2, 75 Jcm-2, 100 Jcm-2, 150 Jcm-2, ou 200 Jcm-2, mesuré à l'aide dudit laser pulsé.
 
4. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel le seuil de détérioration induit par laser est d'au moins 5 MW/cm2, 10 MW/cm2, 20 MW/cm2, ou 50 MW/cm2, mesuré à l'aide dudit laser à onde continue.
 
5. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel le facteur de réflexion au niveau de ladite au moins une surface n'est pas supérieur à 1,5%, 1%, ou 0,5%, à la longueur d'onde de fonctionnement de l'élément optique.
 
6. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel l'élément optique a un facteur de transmission d'au moins 97%, 98%, ou 99%, à la longueur d'onde de fonctionnement de l'élément optique.
 
7. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel l'élément optique a une dispersion intégrée totale dans un hémisphère avant qui n'est pas supérieure à 2%, 1%, 0,5%, ou 0,1%, à la longueur d'onde de fonctionnement de l'élément optique.
 
8. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel l'élément optique a un coefficient d'absorption, mesuré à la température ambiante, ≤ 0,4 cm-1, ≤ 0,3 cm-1, ≤ 0,2 cm-1, ≤ 0,1 cm-1, ≤ 0,07 cm-1, ou ≤ 0,05 cm-1 à 10,6 µm.
 
9. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel l'élément optique a un coefficient de perte diélectrique tan δ, mesuré à la température ambiante à 145 GHz, ≤ 2 x 10-4, ≤ 10-4, ≤ 5 x 10-5, ≤ 10-5, ≤ 5 x 10-6, ou ≤ 10-6.
 
10. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel l'élément optique a l'une ou plusieurs des caractéristiques suivantes :

une densité moyenne de points noirs non supérieure à 5 mm-2, 3 mm-2, 1 mm-2, 0,5 mm-2, ou 0,1 mm-2 ;

une distribution de points noirs telle qu'il n'y ait pas plus de 5, 4, 3, 2, ou 1 points noirs à l'intérieur de toute zone de 3 mm2 ;

un facteur d'absorption intégré par unité d'épaisseur non supérieur à 0,20 cm-2, 0,15 cm-2, 0,10 cm-2, ou 0,05 cm-2, mesuré avec un fond linéaire corrigé situé dans une plage comprise entre 2760 cm-1 et 3030 cm-1 ;

une conductivité thermique non inférieure à 1800 Wm-1K-1, 1900 Wm-1K-1, 2000 Wm-1K-1, 2100 Wm-1K-1, ou 2200 Wm-1K-1 ; et

une concentration en silicium, mesurée par spectrométrie de masse d'ions secondaires, non supérieure à 1017 cm-3, 5 x 1016 cm-3, 1016 cm-3, 5 x 1015 cm-3, ou 1015 cm-3.


 
11. Elément optique selon l'une quelconque des revendications précédentes,
dans lequel le motif de surface anti-réfléchissant est formé dans au moins une surface du matériau en diamant synthétique sur une zone d'au moins 50 mm2, 100 mm2, 200 mm2, 300 mm2, 500 mm2, 700 mm2, 1000 mm2, 1500 mm2, 2000 mm2, 3000 mm2, 5000 mm2, 7000 mm2, 10.000 mm2, 15.000 m2, ou 20.000 mm2.
 
12. Elément optique selon la revendication 11,
dans lequel l'élément optique satisfait aux exigences définies dans une ou plusieurs des revendications 1 à 10 sur au moins 50%, 60%, 70%, 80%, 90%, ou 100% de ladite zone.
 
13. Système optique, comprenant :

un élément optique selon l'une quelconque des revendications précédentes ; et

une source de lumière configurée de façon à générer de la lumière à une puissance d'au moins 20 kW et à transmettre ladite lumière par l'intermédiaire de l'élément optique.


 
14. Système optique selon la revendication 13,
dans lequel la source de lumière est configurée de façon à générer de la lumière à une puissance d'au moins 25 kW, 30 kW, 35 kW, 40 kW, 45 kW, ou 50 kW.
 
15. Système optique selon la revendication 13 ou 14, comprenant de plus un système de refroidissement pour refroidir l'élément optique.
 




Drawing








Cited references

REFERENCES CITED IN THE DESCRIPTION



This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

Patent documents cited in the description




Non-patent literature cited in the description