US5408481A
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US
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Intracavity sum frequency generation using a tunable laser containing an active mirror
Assignee: United States Department of the Navy
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Filing: 1994-01-14
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Granted: 1995-04-18
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Expires: 2014-01-14
Abstract
Abstract A means for intracavity sum frequency generation is described in which a er operates simultaneously, cw, at two wavelengths where the net gain at one wavelength is substantially lower than that at the other. The optical alignment of the resonator provides a region where both fundamental wavelengths are overlapped, and another region where both feedback paths are spatially distinct. An active feedback mirror is located in the path of the lower net gain laser transition to provide optical amplification at that wavelength. The laser resonator further contains a sum frequency generating crystal for intracavity sum frequency generation of the two fundamental wavelengths. The sum frequency generating crystal is placed near a laser resonator cavity mode waist in the region where both wavelengths are spatially superimposed, producing the sum frequency of the two wavelengths. An intracavity polarization rotator provides the appropriate orientation of the polarization of the two fundamental wavelengths in the laser gain element as well as in the non-linear sum frequency generating crystal. Line narrowing of the individual two fundamental wavelengths produces a line narrowed sum frequency generated output. Sum frequency generation at 459 nm is demonstrated in a non-critically phase matched Type II KTP crystal by operating a Ti:sapphire laser simultaneously at 808 nm and 1.064 μ.
Inventors
- 👤 Richard Scheps
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-07 11:09
CPC Classifications
H; H01; H01S; H01S3/00; H01S3/05; H01S3/08; H01S3/081; H01S3/0811; H01S3/08086; H01S3/0809; H01S3/09; H01S3/091; H01S3/094; H01S3/094038; H01S3/0941; H01S3/09415; H01S3/10; H01S3/10084; H01S3/10092; H01S3/105; H01S3/106; H01S3/108; H01S3/109; H01S3/14; H01S3/16; H01S3/1601; H01S3/162; H01S3/1623; H01S3/163; H01S3/1645; H01S3/1648
Claims Analysis
Total Claims: 45
Claim 1
Independent Claim
344 words
A laser generating two wavelengths simultaneously within a preselected range of wavelengths for producing a third wavelength by sum frequency generation comprising: a laser resonator for said two wavelengths generated simultaneously within said preselected range of wavelengths defining a laser resonator cavity by two end reflective elements, three highly reflective concave fold mirror elements and an output coupler reflective element arranged to form a reflective path for a laser resonator mode in said laser resonator cavity, at least one of said two end reflective elements being an active mirror, said active mirror being disposed to receive an optical pumping wavelength and having a substrate which provides optical gain at one of said two wavelengths when optically pumped with said optical pumping wavelength, said active mirror being coated on its exterior face to provide high reflectivity for said one of said two wavelengths and to provide high transmission for said optical pumping wavelength, and said active mirror being coated on its interior face to provide low reflectivity at said one of said two wavelengths; a dispersing prism disposed in said laser resonator cavity between one of said concave fold mirror elements and said two end reflective elements to spatially disperse said two wavelengths, said dispersing prism and said two end reflective elements being aligned in a manner such that each of said two end reflective elements defines a discrete end region of a separate one of two feedback paths in said laser resonator cavity, each of said two feedback paths being for a discrete one of said two wavelengths in said preselected range of wavelengths; a laser gain element disposed in said laser resonator cavity to produce laser emission including said two wavelengths in said preselected range of wavelengths; means for optically exciting said laser gain element in an end pumping mode to produce said laser emission that includes said two wavelengths in said preselected range of wavelengths; and a non-linear optical crystal located within said laser resonator cavity having the property to generate said third wavelength being the sum frequency of said two wavelengths.
Claim 2
Dependent Claim
344 words
A laser generating two wavelengths simultaneously within a preselected range of wavelengths for producing a third wavelength by sum frequency generation comprising: a laser resonator for said two wavelengths generated simultaneously within said preselected range of wavelengths defining a laser resonator cavity by two end reflective elements, three highly reflective concave fold mirror elements and an output coupler reflective element arranged to form a reflective path for a laser resonator mode in said laser resonator cavity, at least one of said two end reflective elements being an active mirror, said active mirror being disposed to receive an optical pumping wavelength and having a substrate which provides optical gain at one of said two wavelengths when optically pumped with said optical pumping wavelength, said active mirror being coated on its exterior face to provide high reflectivity for said one of said two wavelengths and to provide high transmission for said optical pumping wavelength, and said active mirror being coated on its interior face to provide low reflectivity at said one of said two wavelengths; a dispersing prism disposed in said laser resonator cavity between one of said concave fold mirror elements and said two end reflective elements to spatially disperse said two wavelengths, said dispersing prism and said two end reflective elements being aligned in a manner such that each of said two end reflective elements defines a discrete end region of a separate one of two feedback paths in said laser resonator cavity, each of said two feedback paths being for a discrete one of said two wavelengths in said preselected range of wavelengths; a laser gain element disposed in said laser resonator cavity to produce laser emission including said two wavelengths in said preselected range of wavelengths; means for optically exciting said laser gain element in an end pumping mode to produce said laser emission that includes said two wavelengths in said preselected range of wavelengths; and a non-linear optical crystal located within said laser resonator cavity having the property to generate said third wavelength being the sum frequency of said two wavelengths.
Claim 3
Dependent Claim
49 words
The laser of claim 1 in which said active mirror is optically pumped in an end pumping mode, and one of said three fold mirror elements is located within said laser resonator cavity to produce a laser resonator cavity mode waist at said exterior face of said active mirror.
Claim 4
Dependent Claim
17 words
The laser of claim 2 in which the laser gain element is a solid state gain element.
Claim 5
Dependent Claim
26 words
The laser of claim 3 in which said solid state gain element is a Ti:sapphire gain element, and said substrate of said active mirror is Nd:YAG.
Claim 6
Dependent Claim
67 words
The laser of claim 4 in which said first wavelength of said two wavelengths is approximately 808 nm and said second wavelength of said two wavelengths is 1.064 μ, said non-linear optical crystal for generating said sum frequency is a Type II KTP crystal non-critically phase matched for sum frequency generation at approximately 25° C. and said sum frequency of said third wavelength is approximately 459 nm.
Claim 7
Dependent Claim
48 words
The laser of claim 3 in which said solid state gain element is a crystalline material that includes a host material doped with activator ions to produce said laser emission in said preselected range of wavelengths when said crystal line material is optically excited by end pumping thereof.
Claim 8
Dependent Claim
68 words
The laser of claim 6 in which said host material is a sapphire host material and said activator ions in said sapphire host material include a dopant of Ti 3+ ions to enable said crystalline material to produce said laser emission within said preselected range of wavelengths from about 680 nm to 1.1 μ when said solid state gain element is optically excited by said optically exciting means.
Claim 9
Dependent Claim
16 words
The laser of claim 2 in which said laser gain element is a liquid gain element.
Claim 10
Dependent Claim
17 words
The laser of claim 8 in which said liquid gain element is a dye solution gain element.
Claim 11
Dependent Claim
16 words
The laser of claim 2 in which said laser gain element is a gaseous gain element.
Claim 12
Dependent Claim
16 words
The laser of claim 2 in which said laser gain element is a semiconductor gain element.
Claim 13
Dependent Claim
17 words
The laser of claim 2 in which said active mirror is optically pumped by a laser diode.
Claim 14
Dependent Claim
82 words
The laser of claim 12 in which the output of said laser diode used in said end pumping mode is focused onto said exterior face of said active mirror so that the pump focus size is approximately the same as said laser resonator cavity mode waist at said exterior face, and the divergence of the focused output of said laser diode within said active mirror is approximately the same as the divergence of said laser resonator cavity mode within said active mirror.
Claim 15
Dependent Claim
68 words
The laser of claim 2 in which said one of said two end reflective elements is a partial reflector which transmits one of said two wavelengths, and the other of said two end reflective elements is said active mirror, and said one of said two wavelengths is transmitted through said partial reflector and directed to said exterior face of said active mirror to optically pump said active mirror.
Claim 16
Dependent Claim
15 words
The laser of claim 2 in which said non-linear optical crystal is a KTP crystal.
Claim 17
Dependent Claim
34 words
The laser of claim 2 in which each of said two wavelengths is linearly polarized and the orientation of the polarization of each of said two wavelengths is parallel within said laser gain element.
Claim 18
Dependent Claim
72 words
The laser of claim 2 in which said non-linear optical crystal is configured for Type II sum frequency generation, and further including: means disposed in said laser cavity for rotating the polarization of one wavelength of said two wavelengths 90° with respect to the other wavelength of said two wavelengths, the rotating means is disposed to effect the polarization rotation within said non-linear optical crystal but not in said laser gain element.
Claim 19
Dependent Claim
17 words
The laser of claim 17 in which said polarization rotating means is a multiple order wave plate.
Claim 20
Dependent Claim
49 words
The laser of claim 2 in which said output coupler is a concave output coupler disposed relative to one of said three concave fold mirror elements to produce a nearly concentric laser cavity mode therebetween and to produce a laser resonator cavity mode waist in said non-linear optical crystal.
Claim 21
Dependent Claim
19 words
The laser of claim 2 in which said non-linear optical crystal is non-critically phase matched for sum frequency generation.
Claim 22
Dependent Claim
29 words
The laser of claim 2 in which one region of said laser resonator cavity contains both of said two wavelengths arranged in a spatially collinear and spatially overlapped relationship.
Claim 23
Dependent Claim
50 words
The laser of claim 21 in which said one region in which said both of said two wavelengths are spatially collinear and spatially overlapped contains said non-linear optical crystal for generating said third wavelength by sum frequency generation, said two wavelengths thereby being spatially superimposed within said non-linear optical crystal.
Claim 24
Dependent Claim
31 words
The laser of claim 22 in which another region of said laser resonator cavity contains both of said two wavelengths where each of said two wavelengths are spatially separated and distinct.
Claim 25
Dependent Claim
75 words
The laser of claim 23 in which said laser operates simultaneously at a first wavelength and at a second wavelength of said two wavelengths, the net gain in said laser gain element for said first wavelength being substantially higher than the net gain in said laser gain element for said second wavelength, and said active mirror located in a feedback path of said another region provides optical amplification for spatially separated and distinct second wavelength.
Claim 26
Dependent Claim
51 words
The laser of claim 24 in which said active mirror provides optical gain for said second wavelength as said laser resonator mode passes through said active mirror substrate, said active mirror being coated on its said exterior face to reflect the amplified said second wavelength back into said laser resonator cavity.
Claim 27
Dependent Claim
20 words
The laser of claim 2 in which the geometry of said active mirror is that of a plane parallel plate.
Claim 28
Dependent Claim
21 words
The laser of claim 2 in which the geometry of said active mirror approximates that of a right angle isosceles prism.
Claim 29
Dependent Claim
30 words
The laser of claim 2 further including: means disposed in said laser cavity for narrowing the linewidth of at least one of said two wavelengths operating simultaneously in said laser.
Claim 30
Dependent Claim
24 words
The laser of claim 28 in which said means for narrowing includes two etalon plates of different thicknesses disposed in said laser resonator cavity.
Claim 31
Dependent Claim
36 words
The laser of claim 2 further including: a single etalon plate disposed in said laser resonator cavity for simultaneously narrowing the linewidth of both of said two wavelengths to produce a line narrowed said third wavelength.
Claim 32
Dependent Claim
40 words
The laser of claim 2 in which said laser is continuously tunable over said preselected range of wavelengths and at least one of said two reflective end elements is rotatable to provide a tunable said sum frequency said third wavelength.
Claim 33
Dependent Claim
39 words
The laser of claim 2 in which said laser gain element is a solid state gain element with Brewster cut end faces to provide a polarized laser mode for both of said two wavelengths within said laser resonator cavity.
Claim 34
Dependent Claim
25 words
The laser of claim 2 in which said two wavelengths operate simultaneously in the lowest order transverse spatial mode over said preselected range of wavelengths.
Claim 35
Dependent Claim
13 words
The laser of claim 2 in which said two wavelengths are produced cw.
Claim 36
Dependent Claim
42 words
The laser of claim 2 further including a means disposed within said laser resonator cavity for periodically interrupting said generation of said two wavelengths to produce a repetitively Q-switched output of said third wavelength being the sum frequency of said two wavelengths.
Claim 37
Dependent Claim
45 words
The laser of claim 2 in which said substrate of said active mirror is approximately 1.1% Nd 3+ in YAG, said substrate of said active mirror is optically pumped at approximately 808 nm to provide optical amplification at 1.064 μ within said laser resonator cavity.
Claim 38
Dependent Claim
51 words
The laser of claim 2 in which said one of said three fold mirrors is disposed and oriented to locate said laser resonator cavity mode waist at said exterior face of said active mirror and is used at a low angle of incidence with respect to said laser resonator cavity mode.
Claim 39
Dependent Claim
28 words
The laser of claim 2 in which said laser is continuously tunable to produce cw simultaneous laser emission at any two wavelengths within said preselected range of wavelengths.
Claim 40
Dependent Claim
22 words
The laser of claim 38 in which said sum frequency said third wavelength is continuously tunable over a preselected range of wavelengths.
Claim 41
Dependent Claim
88 words
The laser of claim 2 in which said dispersing prism is oriented in a minimum deviation configuration and has two optical faces oriented at Brewster's angle with respect to the laser resonator cavity mode, and said dispersing prism being rotatable to determine said two wavelengths which are simultaneously generated within said preselected range of wavelengths, and oriented to provide substantial dispersion for said two wavelengths to produce spatially separate and spatially distinct feedback paths for each of said two wavelengths in a region of said laser resonator cavity.
Claim 42
Dependent Claim
21 words
The laser of claim 40 in which said dispersing prism is highly dispersive and is composed of a Faraday rotator glass.
Claim 43
Dependent Claim
16 words
The laser of claim 41 in which said dispersing prism is composed of SF 55 glass.
Claim 44
Dependent Claim
21 words
The laser of claim 1 in which said means for optically exciting said laser gain element is an argon ion laser.
Claim 45
Dependent Claim
21 words
The laser of claim 1 in which said means for optically exciting said laser gain element is a doubled Nd:YAG laser.
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