# US 9,753,352 B1 · High damage threshold frequency conversion system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,753,352 B1 - Document ID: US9753352B1 - Status: Granted - Kind: B1 - Application number: 14/838,686 - Filed: 2015-08-28 - Granted: 2017-09-05 - Earliest claimed: 2010-11-14 - Assignees: KLA-Tencor Corporation - Applicants: KLA-Tencor Corporation - Inventors: J. Joseph Armstrong - Web page: https://patentgrep.com/patent/US9753352B1 ## CPC - G02F 1/3532: {Arrangements of plural nonlinear devices for generating multi-colour light beams, e.g. arrangements of SHG, SFG, OPO devices for generating RGB light beams} - G01N 21/8806: {Specially adapted optical and illumination features} - G01N 21/9501: {Semiconductor wafers (manufacturing processes per se of semiconductor devices implementing a measuring step H10P74/20)} - G02B 3/06: with cylindrical or toric faces - G02B 5/3066: {involving the reflection of light at a particular angle of incidence, e.g. Brewster's angle} - G02B 27/0025: {for optical correction, e.g. distorsion, aberration} - G02B 27/141: {using dichroic mirrors} - G02B 27/28: for polarising (used in stereoscopes G02B30/25) - G02F 1/37: for second-harmonic generation {(G02F1/3532 takes precedence)} - H01S 3/0092: {Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity (nonlinear frequency conversion per se G02F1/35)} - H01S 3/109: Frequency multiplication, e.g. harmonic generation - G01N 2201/06113: Coherent sources; lasers - G01N 2201/068: Optics, miscellaneous - G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) - G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract The present invention includes a fundamental laser light source configured to generate fundamental wavelength laser light, a first nonlinear optical crystal configured to generate first alternate wavelength light, a second nonlinear optical crystal configured to generate second alternate wavelength light, a set of Brewster angle wavefront processing optics configured to condition the first and second alternate wavelengths of light, and a harmonic separator configured to receive the first alternate wavelength light and the second alternate wavelength light from the set of Brewster angle wavefront processing optics, the harmonic separator configured to at least partially separate the first alternate wavelength light from the second alternate wavelength light. ## Claims ### Claim 1 An apparatus for laser frequency conversion having a high damage threshold, comprising: a fundamental laser light source configured to generate fundamental wavelength laser light; a first nonlinear optical crystal configured to receive fundamental laser light from the fundamental laser light source, the first nonlinear optical crystal configured to generate first alternate wavelength light by frequency converting at least a portion of the received fundamental laser light to first alternate wavelength light; a second nonlinear optical crystal configured to receive first alternate wavelength light from the first nonlinear optical crystal, the second nonlinear optical crystal configured to generate second alternate wavelength light by frequency converting at least a portion of the received first alternate wavelength light to second alternate wavelength light; a set of Brewster angle wavefront processing optics configured to receive first alternate wavelength light and second alternate wavelength light from the second nonlinear optical crystal, the set of Brewster angle wavefront processing optics further configured to condition the first alternate wavelength light and second alternate wavelength light emanating from the second nonlinear optical crystal; and a harmonic separator configured to receive the first alternate wavelength light and the second alternate wavelength light from the set of Brewster angle wavefront processing optics, the harmonic separator configured to at least partially separate the first alternate wavelength light from the second alternate wavelength light. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the first nonlinear optical crystal is configured for second harmonic generation. ### Claim 3 (depends on 1) The apparatus of claim 1, wherein the second nonlinear optical crystal is configured for second harmonic generation. ### Claim 4 (depends on 1) The apparatus of claim 1, further comprising: an additional nonlinear optical crystal configured to receive second alternate wavelength light from the second nonlinear optical crystal, the additional nonlinear optical crystal configured to generate an alternate wavelength light by frequency converting at least a portion of the received second alternate wavelength light to an additional alternate wavelength light. ### Claim 5 (depends on 1) The apparatus of claim 1, further comprising: one or more dichroic harmonic separation elements configured to separate the fundamental light from the first alternate light, the one or more dichroic harmonic separation elements configured to direct at least a portion of the first alternate light to the second nonlinear optical crystal. ### Claim 6 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics comprises: at least one lens. ### Claim 7 (depends on 6) The apparatus of claim 6, wherein the at least one lens comprises: at least one fused silica lens or at least one calcium fluoride lens. ### Claim 8 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics comprises: a first lens and a second lens. ### Claim 9 (depends on 8) The apparatus of claim 8, wherein a surface of the first lens or a surface of the second lens comprises a cylindrical surface. ### Claim 10 (depends on 8) The apparatus of claim 8, wherein the set of Brewster angle wavefront processing optics are configured to adjust the separation between the first lens and the second lens in order to adjust for astigmatism in at least one of the first alternate wavelength light or second alternate wavelength light. ### Claim 11 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics are configured to correct for astigmatism in at least one of the first alternate wavelength light or the second alternate wavelength light. ### Claim 12 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics are configured to focus at least one of the first alternate wavelength light or the second alternate wavelength light. ### Claim 13 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics are configured to collimate at least one of the first alternate wavelength light or the second alternate wavelength light. ### Claim 14 (depends on 1) The apparatus of claim 1, wherein the set of Brewster angle wavefront processing optics are configured to correct abberative effects in at least one of the first alternate wavelength light or the second alternate wavelength light. ### Claim 15 (depends on 1) The apparatus of claim 1, wherein the harmonic separator comprises: a harmonic separation element, the harmonic separation element having a first Brewster angle surface, a total internal reflection (TIR) surface, and a second Brewster angle surface, the TIR surface between the first Brewster angle surface and the second Brewster angle surface. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the TIR surface comprises: a curved TIR surface, wherein the curved TIR surface is configured to focus light reflected from the TIR surface. ### Claim 17 (depends on 15) The apparatus of claim 15, wherein at least one of the first Brewster angle surface or the second Brewster angle surface is curved in order to compensate for aberrations produced by a curvature of the TIR surface. ### Claim 18 (depends on 15) The apparatus of claim 15, further comprising: a Brewster angle element configured to compensate for aberrations produced by a curvature of the TIR surface. ### Claim 19 (depends on 15) The apparatus of claim 15, wherein the at least one lens comprises: at least one fused silica lens or at least one calcium fluoride lens. ### Claim 20 (depends on 1) The apparatus of claim 1, wherein the harmonic separator comprises: a first harmonic separation element and a second harmonic separation element. ### Claim 21 (depends on 1) The apparatus of claim 1, wherein the harmonic separator comprises: a harmonic separation element and a Brewster angle element, the Brewster angle element configured to receive a first wavelength of light and a second wavelength of light from the first harmonic separation element. ### Claim 22 An apparatus for laser frequency conversion having a high damage threshold, comprising: a fundamental laser light source configured to generate fundamental wavelength laser light; at least one nonlinear optical crystal configured to generate alternate wavelength light by frequency converting at least a portion of received laser light to alternate wavelength light; a set of Brewster angle wavefront processing optics configured to receive fundamental wavelength light and alternate wavelength light from the nonlinear optical crystal, the set of Brewster angle wavefront processing optics further configured to condition the fundamental wavelength light and the alternate wavelength light emanating from the nonlinear optical crystal; and a harmonic separator configured to receive fundamental wavelength light and alternate wavelength light from the set of Brewster angle wavefront processing optics, the harmonic separator configured to at least partially separate the fundamental wavelength light from the alternate wavelength light. ### Claim 23 A method for laser frequency conversion with high damage threshold, comprising: providing a fundamental laser light source; generating fundamental wavelength laser light utilizing the fundamental laser light source; generating first alternate wavelength light by frequency converting at least a portion of the fundamental laser light to first alternate wavelength light utilizing a first nonlinear optical crystal; generating second alternate wavelength light by frequency converting at least a portion of the first alternate wavelength light to second alternate wavelength light utilizing a second nonlinear optical crystal; conditioning the first alternate wavelength light and second alternate wavelength light utilizing Brewster angle wavefront processing optics; and separating at least a portion of the first alternate wavelength light from the second alternate wavelength light utilizing a harmonic separator including a harmonic separation element having a first Brewster angle surface, a total internal reflection surface, and a second Brewster angle surface.