Multipass geometry and constructions for diode-pumped solid-state lasers and fiber lasers, and for optical amplifier and detector
First Claim
1. In a method in constructing a zig-zag slab laser with an one-dimensional beam-expanding laser cavity, capable of i) realizing intense multipass pumping, ii) effectively solving thermal distortion and cooling problems, iii) providing stress-free and O-ring-free slab mounting, iv) obtaining high-power TEM00-mode operation, v) achieving extra-high-power intracavity SHG, vi) operating in either CW mode or pulsed mode, and vii) minimizing spatial hole burning whereby realizing high power operation at minor laser lines, comprising the steps ofA. selecting a pump source means, from the group consisting of a diode bar means and a multiple-pump-source means having a single pump wavelength or multiple pump wavelengths, to provide a relevant pumping light for pumping;
- B. making a laser slab means, wherein said laser slab means has a substantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut;
C. constructing a slab laser pump head for pumping, housing and cooling said laser slab means;
D. constructing said one-dimensional beam-expanding laser cavity by mean of an one-dimensional prism beam expander means, wherein (1) said laser cavity includes at least two cavity mirrors, (2) said pump head is placed within said laser cavity for lasing at a fundamental wavelength, (3) said one-dimensional beam-expanding laser cavity causes laser light to resonate along a zig-zag optical path between said two major surfaces of said laser slab means via total-internal-reflection, (4) said laser cavity has a noncircular or line-shaped spatial mode cross-section at least within part of said laser cavity which is substantially compatible with the cross-section of said laser slab means, and (5) whereby i) obtaining mode-matched pumping, TEM00-mode operation and all-out energy extraction from said laser slab means, ii) employing said laser slab means with a large aspect ratio of its height to its thickness, so as to effectively solve thermal distortion problems, and iii) achieving high-performances of intracavity harmonic generations and true CW operation over wide spectra ranges, from red, blue to ultraviolet; and
E. optionally inserting a Q-switch into the expanded mode portion of said cavity for a pulsed mode operation, wherein the cross-section of the laser beam which passes through said Q-switch is a line rather than a point, so that the power density impinged on said Q-switch is decreased significantly, whereby avoiding optical damages and acquiring extra-high energy operations.
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Abstract
In order to effectively solve thermal distortion problems and obtain high-power TEM00-mode operations for DPSS lasers, two major steps are presented in this invention. First, novel multipass pumping approaches and corresponding engineering designs have been developed for slab lasers and thin-disk lasers. They are characterized by using multipass and zig-zag pumping paths and confining pumping beams substantially via total-internal-reflection (TIR) to significantly reduce multiple reflection losses. Second, a zig-zag slab laser in combination with a beam-expanding cavity is employed to realize mode-matching pumping and maximize the energy extraction from laser slabs. It also leads to achieving high-power intracavity frequency conversions over wide spectral ranges and producing red and blue visible lasers with the aid of minimizing spatial hole burning. Besides, the invented optical multipass geometry and TIR-guide constructions can also be utilized for pumping rod lasers, fiber lasers and fiber amplifiers, and for optical amplifiers and optical or spectral detectors.
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Citations
30 Claims
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1. In a method in constructing a zig-zag slab laser with an one-dimensional beam-expanding laser cavity, capable of i) realizing intense multipass pumping, ii) effectively solving thermal distortion and cooling problems, iii) providing stress-free and O-ring-free slab mounting, iv) obtaining high-power TEM00-mode operation, v) achieving extra-high-power intracavity SHG, vi) operating in either CW mode or pulsed mode, and vii) minimizing spatial hole burning whereby realizing high power operation at minor laser lines, comprising the steps of
A. selecting a pump source means, from the group consisting of a diode bar means and a multiple-pump-source means having a single pump wavelength or multiple pump wavelengths, to provide a relevant pumping light for pumping; -
B. making a laser slab means, wherein said laser slab means has a substantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut;
C. constructing a slab laser pump head for pumping, housing and cooling said laser slab means;
D. constructing said one-dimensional beam-expanding laser cavity by mean of an one-dimensional prism beam expander means, wherein (1) said laser cavity includes at least two cavity mirrors, (2) said pump head is placed within said laser cavity for lasing at a fundamental wavelength, (3) said one-dimensional beam-expanding laser cavity causes laser light to resonate along a zig-zag optical path between said two major surfaces of said laser slab means via total-internal-reflection, (4) said laser cavity has a noncircular or line-shaped spatial mode cross-section at least within part of said laser cavity which is substantially compatible with the cross-section of said laser slab means, and (5) whereby i) obtaining mode-matched pumping, TEM00-mode operation and all-out energy extraction from said laser slab means, ii) employing said laser slab means with a large aspect ratio of its height to its thickness, so as to effectively solve thermal distortion problems, and iii) achieving high-performances of intracavity harmonic generations and true CW operation over wide spectra ranges, from red, blue to ultraviolet; and
E. optionally inserting a Q-switch into the expanded mode portion of said cavity for a pulsed mode operation, wherein the cross-section of the laser beam which passes through said Q-switch is a line rather than a point, so that the power density impinged on said Q-switch is decreased significantly, whereby avoiding optical damages and acquiring extra-high energy operations. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. In a method in constructing a multipass pump head for DPSS lasers, fiber lasers and fiber amplifiers, capable of realizing intense uniform pumping and producing and amplifying coherent light, comprising the steps of
A. selecting a pump source means, from the group consisting of a diode bar means and a multiple-pump-source means having a single pump wavelength or multiple pump wavelengths, to provide a relevant pumping light for pumping; -
B. selecting a laser medium means from the group including (1) laser chips, laser rods and laser slabs, made from regular laser materials or tunable laser materials, and (2) optical fibers with a rare-earth-doped core;
C. setting a coupling manner to couple said pumping light to a pump entrance means including at least one pump entrance for the input of said pumping light into said multipass pump head; and
D. constructing said multipass pump head by use of a multipass formation to confine said pumping light, wherein said pumping light, once entering, undergoes multiple reflections and multiple travels through or within said laser medium means, said multipass formation is selected from the group consisting of (1) a first multipass formation with the use of optical total-internal-reflection configuration, which additionally comprises the steps of making said multipass pump head as a TIR-guide pump head by mean of an optical duct means, leading to confining said pumping light within said TIR-guide pump head mainly via total-internal-reflection during the entire pumping process;
wherein i) said pumping light, once entering said pump head and said optical duct means, will undergo zig-zag optical paths, multiple reflections and multiple travels through or within said laser medium means until it is absorbed, and ii) the escape loss possibility of unabsorbed said pumping light is at least less than 40% within one round trip pumping path, or at least less than 40% during the entire pumping process;
whereby i) significantly reducing multiple reflection losses caused by the zig-zag optical paths, ii) confining said pumping light within said pump head to achieve effective and efficient uniform pumping; and
iii) with the use of said optical duct means, eliminating hot spot issue caused by directly diode bar pumping for DPSS lasers;
(2) a second multipass formation with the use of optical graded-index or step-index configuration, (3) a third multipass formation with the use of a noncircular-profile reflector means which has a noncircular cross-section with a convex and closed boundary, wherein i) said laser medium means is a laser rod means which has a lasing axis and a transverse plane perpendicular to said lasing axis, said noncircular cross-section is in said transverse plane, ii) said laser rod is surrounded by a cooling channel, and iii) the maximum dimension inside said noncircular cross-section is at least four-times larger than the diameter of said laser rod means, (4) a fourth multipass formation with the use of a double-layer reflector means, (5) a fifth multipass formation with the use of optical spatial filter configuration, (6) a sixth multipass formation with the use of a reflector means, wherein i) said laser medium means is a laser slab means which has a sunbstantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut, ii) said laser slab means is cooled via said two major surfaces only, iii) said diode bar means comprises at least one linear array laser diode bar or 2-D stacked diode bar, iv) each said pump entrance receives said pumping light from one or several said diode bars without fiber coupling, and v) said pump light enters said reflector means and multiply passes through said laser slab means via said two major surfaces, (7) a seventh multipass formation with the use of a noncircular-profile reflector means which has a noncircular cross-section, wherein i) said laser medium means is a laser slab means which has a substantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut, ii) said laser slab means is mounted into a laser slab assembly means without O-rings, preferably via a silicone RTV, in which said laser slab means is sandwiched between two coolant passages via said two major surfaces, iii) the flow direction along said coolant passages is perpendicular to said minor surfaces of said laser slab, and iv) said pump light enters said noncircular-profile reflector means and multiply passes through said laser slab means via said two major surfaces, (8) an eighth multipass formation with the use of an optical duct means, wherein a) said laser medium means is a laser slab means which has a substantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut, b) said optical duct means consists of two members of thin planar optical duct at least, each one has two broad surfaces, c) said laser slab means is sandwiched between said two members of thin planar optical duct via said major surfaces firstly, and then sandwiched between two heat sinks via said two members of thin planar optical duct symmetrically, d) said optical duct means is optically coupled to two said major surfaces of said laser slab means via its said broad surfaces where said pumping light runs into said laser slab means along zig-zag optical paths, e) said optical duct means is of high thermal conductivity and thermally in contact with said two heat sink via its said broad surfaces, said laser slab means is conductively cooled via said optical duct means, f) in order to preserve the TIR interface for the laser zig-zag path within said laser slab means, an approach is selected from the group including;
i) said laser slab means has a protective coating, and ii) said optical duct means has a lower refractive index than that of said laser slab means,g) optically the end of said thin planar optical duct adjacent to said laser slab means is gold coated but not square-cut in order to change the incident angle of said pumping light for effective pumping, h) optionally said heat sink has a mirrored surface which is interfaced with said broad surfaces of said thin planar optical duct whereby to reflect said pumping light and realize multipass pumping, i) optionally part of the additional members of optical duct have a tapered shape, and j) optionally lateral sides of said optical duct have a gold coating in order to reflect said pumping light while said optical duct means has a low refractive index, (9) a ninth multipass formation with the use of an optical duct means, wherein a) said laser medium means is a laser slab means which has a substantially rectangular cross section with two major surfaces, two minor surfaces, and two opposing end faces which are cut at a Brewster angle or square-cut, b) one said major surface of said laser slab means is interfaces with said optical duct means, the other one of said major surfaces is conductively cooled, c) said pumping light, once entering said optical duct means, will undergo zig-zag optical paths, multiple reflections and multiple travels through said laser slab means until it is absorbed;
d) said pumping light enters said laser slab means via its major surface, e) for the cooling side of said slab means, in order to reflect pumping light and to preserve the TIR interface for the laser zig-zag path within said laser slab means, an approach is selected from the group including;
i) it is covered by a metal foil which may have a high reflectivity, ii) it is interfaced with a metalized mirror surface of a heat sink, and iii) it is HR coated at the pump wavelength, and the SiO2 or MgF2 material is used as the first layer of the HR coating,f) for the non-cooling side of said slab means, in order to preserve the TIR interface for the laser zig-zag path within said laser slab means, an approach is selected from the group including;
i) it has a protective coating or bonding material, ii) it has a MgF2 window, iii) said optical duct has a lower refractive index than said slab means, and iv) it is distanced from said optical duct means with an interstitial air,g) optionally one side of said optical duct has a gold coating in order to reflect said pumping light, and h) optionally part of said optical duct means have a tapered shape, and (10) a tenth multipass formation with the use of a reflector means, wherein i) said laser medium means is an optical fiber means with a rare-earth-doped core, ii) said diode bar means comprises at least one linear array laser diode bar or 2-D stacked diode bar, iii) said pumping light from one or several said diode bars are optically coupled to one said pump entrance, and iv) said pump light enters said reflector means and multiply passes through said optical fiber means; and
E. housing and cooling said laser medium means. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. In a method in configuring a multipass apparatus by means of an optical TIR-guide disk reflector for thin-disk lasers or multipass light amplifiers, and for optical and spectral detection, including particle detection, comprising the steps of
A. by use of a circular or noncircular disk-shaped optical duct means, constructing said reflector to have parallel two main surfaces perpendicular to an axis and an outer surface parallel to said axis, wherein said two main surfaces are exactly same and their size is larger than the thickness between them; -
B. entering a light toward the center area of said reflector, wherein (1) said optical duct means is optically clear to said light, and (2) said light is directed parallel to and confined between said two main surfaces via total-internal-reflection and undergoes multiple reflections via said outer surface; and
C. in order to confine and reflect said light from said outer surface, selecting an approach from the group including;
(1) first approach, which additionally comprises the steps of making an HR coating selectively covering predetermined portions of said outer surface, and (2) second approach, which additionally comprises the steps of fitting said optical disk into a heat sink chamber means, whose inwardly facing wall matches to said outer surface geometrically and has a gold coating;
whereby said light, once entering said multipass apparatus and said reflector, multiply and repeatedly passes through the center area of said reflector. - View Dependent Claims (27, 28, 29)
B. setting a coupling manner to couple said pumping light to said reflector for pumping, wherein said coupling manner includes optical fiber coupling;
C. constructing a laser chip means to be optically integrated with or embedded into said optical duct means, wherein (1) said optical duct means is transparent at both the pump and laser wavelengths and its refractive index is the same as or close to that of said laser chip means, and (2) an optical joint approach is used for the joint of said laser chip means and said optical duct means, which is selected from the group including, i) interposing a high temperature optical-grade epoxy or cement, ii) diffusion-bonding, and iii) frit;
D. selecting the shape of said two main surfaces from the group including (1) a circular shape, wherein i) said HR coating is at the pumping light wavelength and ii) at least one AR coated narrow spectral opening or uncoated narrow opening on said outer surface for inputting the pumping light, said optical duct means is made from the group including a) regular optical duct, said pump head is named the TIR-Guide Disk Pump Head, wherein said laser chip is eccentrically located about said optical duct means, b) graded-index optical duct, wherein said optical duct means has a variable refractive index in the radial direction, whereby said pumping light, once entering, to be refocussed by refraction into the center area of said pump head periodically and leading to a large acceptance cone, said pump head is named the Graded-Index TIR-Guide Disk Pump Head, and c) step-index optical duct, wherein said optical duct means has two sleeves with a predetermined radial extent in which the inner sleeve has a lower refractive index than that of the outer sleeve appropriately, whereby said pumping light, once entering, to be continually converged to the center area of said pump head and leading to a large acceptance cone, said pump head is named the Step-Index TIR-Guide Disk Pump Head, and (2) a non-circular shape, said pump head is named the Noncircular-Profile TIR-Guide Disk Pump Head, wherein i) said HR coating is at the pumping light wavelength, and ii) at least one AR coated narrow spectral opening or uncoated narrow opening on said outer surface for inputting the pumping light;
E. conductively cooling said laser chip means surrounded by said optical disk;
wherein i) one side of said optical disk is in thermal connect with an HR mirror or mirrored surface, ii) said mirror has thin substrate with high thermal conductivity, and iii) said HR mirror or said mirrored surface serves as an end or fold mirror for laser operations; and
F. optimizing the optical and physics properties and performance parameters of said pump head in effective operative way, including the profile, size, geometric shape, location and orientation, refractive index and dopant concentration, whereby facilitating efficient and uniform multipass pumping, laser operation and effective cooling.
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28. In the method of claim 26, in order to making a multipass light amplifier of said multipass apparatus to amplify coherent light, further comprising the steps of
A. making said light as a signal input; -
B. selecting a pump source means to provide a relevant pumping light to pump a laser chip means in order to amplify said signal input;
C. constructing said laser chip means to be surrounded by and integrated with said optical duct means, wherein (1) said optical duct means is transparent at both said signal input and said pumping light and its refractive index is the same as or close to that of said laser chip means, and (2) a joint approach is used for the joint of said laser chip means and said optical duct means, which is selected from the group including, i) interposing a high temperature optical-grade epoxy or cement, ii) diffusion-bonding, and iii) frit;
D. constructing said reflector as an optical container to confine said signal input and optionally said pumping light, wherein (1) the shape of said two main surfaces has a circular shape, (2) said signal input, once entering, is confined between said two main surfaces and undergoes multiple reflections in consecutive order clockwise or counterclockwise, and multiple passes through said laser chip means whereby being amplified, (3) said signal input is amplified until outputed from an exit on said outer surface where is an AR coated opening, and (4) said HR coating is at said signal input wavelength and an opening on said outer surface for inputting said signal input;
E. setting a coupling manner to couple said pumping light to said laser chip means for pumping, from the group including (1) a first coupling manner to be used as an axial pumping, wherein said pumping light pumps said laser chip means along said axis, and (2) a second coupling manner to be used as an centripetal pumping, wherein said pumping light is coupled to said outer surface, after entering, undergoes multiple reflections and multiple passes through said laser chip means until it is substantially absorbed, said HR coating is also at said pumping light wavelength and at least one AR coated narrow spectral opening or uncoated narrow opening on said outer surface for inputting said pumping light; and
F. selecting an output manner to output the amplified signal input.
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29. In the method of claim 26, in order to making a multipass laser intensified detector of said multipass apparatus for optical or spectral detection, including multipass absorption and particle detection, further comprising the steps of
A. making said light as a probe laser beam; -
B. making the shape of said two main surfaces to have a circular shape with a center hole, wherein said center hole is a detecting region for said detection;
C. constructing said disk-shaped optical duct means as an optical container to confine said probe laser beam, wherein said probe laser beam, once entering, is confined between said two main surfaces and undergoes multiple reflections in consecutive order clockwise or counterclockwise, and multiple passes through said detecting region for said detection;
D. placing a path compensating ring with a proper refractive index at said center hole so as to correct optical path distortion if there is an important difference of the refractive index between said optical duct means and said detecting region, wherein said ring has an anti-reflection coating for said probe laser beam preferably;
E. setting a detected sample, including gas, liquid and particle, within said detecting region properly; and
F. arranging a detecting means and a detecting approach for said detection.
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30. In a method by means of minimizing spatial hole burning effect in constructing a solid-state laser with high-power operation at a desired minor laser line, particularly for producing over 2-W CW red or blue coherent light via intracavity SHG, comprising the steps of
A. setting a desired output wavelength for said minor laser line; -
B. selecting a pump source means, from the group consisting of a diode bar means and a multiple-pump-source means having a single pump wavelength or the multiple pump wavelengths, to provide a relevant pumping light for pumping;
C. selecting a laser medium means from the group including laser chips, laser slabs and laser rods;
D. constructing a pump head for pumping, housing and cooling said laser medium means, capable of realizing intense uniform pumping;
E. setting a linear laser cavity;
wherein(1) said laser cavity includes at least two cavity mirrors, and (2) said pump head is placed within said laser cavity for lasing at said desired output wavelength;
F. producing a gain region with intense pumping within said laser medium means;
G. maximizing the cavity Q factor of said laser cavity for said desired output wavelength;
H. minimizing the cavity Q factor of said laser cavity for undesired laser lines;
I. locating said gain region at an optimum position, at ½
L, ¼
L, ¾
L, ⅙
L and ⅚
L, wherein i) L is designated as the optical length of said laser cavity, ii) within said optimum position there would be the highest possibility for a pair of longitudinal modes with a spatially anti-correlated relationship to take place and to occupy most of said gain region spatially, whereby minimizing spatial hole burning and restraining said gain region available to undesired major laser lines;
J. making said laser cavity have a large enough optical length L to prolong an out of phase region to best match said gain region, wherein within the out of phase region two peaks in the standing wave patterns corresponding to the pair of anti-correlated longitudinal modes are out of phase;
K. setting said gain region have a limited length to best match the out of phase region, whereby restraining said gain region available to undesired major laser lines;
L. keeping the dopant concentration of said laser medium means as low as possible while keeping the absorption efficiency of said laser medium means high for said pumping light;
M. inserting a nonlinear crystal means into said laser cavity for intracavity frequency conversions, wherein said nonlinear crystal means is selected from the group including (1) a regular nonlinear crystal means, and (2) a periodically poled crystal means with quasi-phase-matching; and
N. optionally employing the gain sweeping technique to produce a continuous oscillatory change in the optical length of said laser cavity to cause the standing wave pattern of said desired output wavelength to oscillate as a traveling wave along said cavity optical path such that the standing wave pattern moves through at least the entire gain region for extracting substantially all of the gain from said gain region, whereby only said desired output wavelength is lasing steadily.
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Specification