Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/02—Constructional details
  • H01S3/04—Arrangements for thermal management
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/09—Processes or apparatus for excitation, e.g. pumping
  • H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
  • H01S3/0915—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light
  • H01S3/092—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of flash lamp
  • H01S3/093—Processes or apparatus for excitation, e.g. pumping using optical pumping by incoherent light of flash lamp focusing or directing the excitation energy into the active medium
  • H01S3/0931—Imaging pump cavity, e.g. elliptical
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/02—Constructional details
  • H01S3/04—Arrangements for thermal management
  • H01S3/042—Arrangements for thermal management for solid state lasers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
  • H01S3/106—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
  • H01S3/108—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
  • H01S3/109—Frequency multiplication, e.g. harmonic generation
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/02—Constructional details
  • H01S3/04—Arrangements for thermal management
  • H01S3/0404—Air- or gas cooling, e.g. by dry nitrogen
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/02—Constructional details
  • H01S3/04—Arrangements for thermal management
  • H01S3/0407—Liquid cooling, e.g. by water
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • 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
  • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
  • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
  • H01S3/06—Construction or shape of active medium
  • H01S3/0602—Crystal lasers or glass lasers
  • H01S3/0612—Non-homogeneous structure

Definitions

• This invention relates in general to solid state laser systems and more particularly to a con ⁇ tinuous wave solid state laser system having an output frequency which is twice that of the laser's fundamen ⁇ tal frequency.
• Laser systems utilizing frequency-doubling solid-state crystals to generate an output beam at a frequency twice the fundamental frequency of the laser rod employed are well known in the art.
• Such systems embody a two-mirror cavity configuration in which reflectors (or mirrors) at either end of the laser rod are " coated to reflect substantially all of the optical energy at the fundament.al frequency while - passing therethough a substantial portion of the opti ⁇ cal beam at twice that frequency.
• a suitable- frequency-doubling crystal such as KTP (potassium titanyl phosphate), manufactured by Airtron, a division of Litton Industries, Inc., of Morris Plains, N.J., is placed between one end of the laser and one of the two mirrors.
• the optical beam at double the fundamental frequency is emitted from the mirrors at either end of the laser.
• substantially half of the energy at the doubled frequency is lost since it is propagated in opposite directions.
• prior art lasers have been capable of operating only in the pulse mode because of the intensity level required at the doubled frequency for the laser to be efficient.
• One approach that has been employed in the past for producing a pulsed, frequency-doubled solid state laser output is a three-mirror L-shaped optical configuration in which at one end the laser cavity has a mirror for reflecting all of the optical energy at the fundamental frequency which is incident upon it.
• a folding mirror i.e., a mirror 5 which is coated for reflection of the fundamental fre ⁇ quency only and positioned at a 45° angle relative to the incident beam
• a folding mirror is placed centered on the axis of the laser rod to reflect the beam from the laser rod in a direction normal thereto.
• a third reflecting mirror is placed centered on the axis of the laser rod to reflect the beam from the laser rod in a direction normal thereto.
• the folding mirror is characterized by pro ⁇ viding substantially total reflection of optical energy incident thereon which is at the fundamental frequency
• the frequency-doubled light output is emitted from the laser only at one place, i.e., along the axis through
• Cooling techniques such as the insertion of an optical filter between the excitation lamp and the laser rod to reduce radiation incident on the laser rod which is not useful for producing excitation at the fundamental frequency, have been utilized, and fluid cooling as well as coating of both the laser rod and the excitation lamp ⁇ ' have also been employed.
• a stabilized firequency- doubled CW output in the TEMoo mode had not heretofore been achieve —in part because of non-uniforra cooling of the laser rod.
• cooling of the laser rod is accomplished by convective transfer of heat from • the laser rod into the cooling fluid flowing over the surface of the rod. This causes uneven cooling of the rod surface in both time and space.
• the resulting tem ⁇ perature variations create optical distortions because of the dependency of the index of refraction of the laser rod on temperature.
• the effect of the optical distortions on the output power from the laser depends in turn on the laser resonator mirror geometry. This effect is most severe when the laser is operating in the fundamental mode. A time-dependent cavity loss is generated in this case from these optical distortions and results in a significant variation in output power.
• This output power variation becomes very severe when the fundamental mode is designed to fill most of the rod volume, as in the TEMoo mode, because space is occupied out to the periphery of the laser rod where the index of refraction variations are the greatest. 5
• I ⁇ tical laser pump cavity including a Nd: YAG laser rod, a_ suitable excitation lamp and a frequency-doubling crystal.
• the system optics are arranged to provide for employment of the full diameter of the laser rod, that is, in the TEMoo transverse mode at the fundamental
• pump cavity together with a cooling jacket of specific size and materials (such as Spinel or quartz) cladding the- laser rod. Also, by the use of a specifically- sized orifice for the pump cavity the fluid flow across the surface of the laser rod can be maintained laminar
• Either the cladding or the laminar fluid flow can provide sufficient cooling so as to maintain uni ⁇ form temperature along the length of the laser rod and thereby a stable output power level.
• FIG. 1 is an illustration in generally block diagrammatic form of a frequency-doubled solid state laser constructed in accordance with the principles of this invention.
• FIG. 2 is a generally cross-sectional, diagrammatic view of an embodiment of an optical laser cavity suitable for employment in the system of FIG. 1.
• FIG. 3 is a cross-sectional, generally diagrammatic view, taken along the line 3-3 of FIG. 2, of the embodiment of the optical laser cavity shown in FIG. 2.
• FIG. 4 is a cross-sectional, generally diagrammatic view of a modified embodiment of the opti ⁇ cal laser cavity suitable for employment in the system of FIG. 1.
• ⁇ FIG. 5 is a-c*oss-sectional, generally daigrammatic view, taken along the line 5-5 of FIG. 4, of the modified embodiment of the optical laser cavity shown in FIG. 4
• the pump cavity 11 encloses a conventional parallel excitation lamp 15 which is optically coupled to an elongated solidstate laser rod 13, typically a 4 mm diameter Nd: YAG rod, which produces along the axis of the rod an output laser beam at typically a wavelength of 1.064 ⁇ m.
• a reflector mirror 17, highly reflective ("H.R.") at 1.064 ⁇ m, is posi-tioned at one end of the laser cavity to reflect the laser beam back along the axis.
• This reflector 17 is formed with an appropriate- coating to reflect substantially all of the incident light which is at a wavelength of 1.064 ⁇ m.
• a folding mirror 19 coated to reflect substantially all of the ⁇ gtrt incident upon it at a wavelength of 1.064 ⁇ m. This light is reflected normal to the axis of the fun- 5 damental beam from the laser rod and is then directed to a concave reflecting mirror 21 coated to reflect substantially all light incident upon it at wavelengths of both 1.064 ⁇ m and 0.532 ⁇ m. Positioned between the folding reflector 19 and the concave reflector 21 is a
• the frequency doubler crystal may be formed of: KTP ' which has the characteristic of converting a portion of the light energy incident upon it at a wave ⁇ length, of 1.064 ⁇ m to a wavelength of 0.532 ⁇ m.
• a focusing ⁇ element 25, which typically is a le ' ns-,* is ⁇ positioned to focus, the longer wave length ⁇ light incident upon the frequency-doubling crystal 23
• the concave reflector 21 also focuses the reflected
• the folding mirror 19 is arranged t ⁇ be substantially transparent to light at the 0.532 ⁇ m wavelength and hence serves as an " exit window from the system for a laser beam of this wave ⁇ length. Since the frequencydoubling is efficient only
• a wave plate 18 may be positioned, if desired, between the end of the laser rod 13 and reflector 17 to rotate the polarization of the beam and align it as necessary.
• the laser pump cavity itself is typically formed of a pyrex glass cylinder 31 of elliptical cross section with the excitation lamp 15 located along one axis and the Nd: YAG laser rod 13 located along the other axis.
• the excitation lamp can be a conventional krypton lamp having a quartz envelope and tungsten electrode such as that available from ILC Company, of Sunnyvale, California, under the designation ILC No. L3243.
• the interior surface of the sidewall of the pyrex cavity 31 is coated with a gold deposit, or other highly-reflective coating, to provide for reflection of the lamp energy onto the laser rod.
• a colored glass filter 34 is positioned between the lamp 15 and the laser rod 13 to absorb , at,portion of radiation from the lamp which- does not Serve "' to excite- the lasing.. energy states of the rod, but yet would heat the rod.
• the entire elliptical cavity 31 is cooled by a fluid such as water and includes a Cooling flow tube 35 around the lamp 15 and a second cooling flow tube 37 positioned around the laser rod 13.
• the flow tubes 35 and 37 may be formed of any suitable material such as uranium-doped quartz providing that it is substantially transparent to light from lamp 15 which is of wave- length effective to excite the laser energy states in rod 13.
• the inner diameter of the flow tube 37 around the 4mm laser rod 13 may suitably be 9.5 mm. The nature of the fluid flow through this tube is effected by the sizing of the orifice.
• This orifice is sized such that the flow through the tube along the surface of the rod is substantially laminar, thereby intro ⁇ ducing a minimum of variation in the cooling action and aintaining the surface of the rod at a stable tempera ⁇ ture distribution.
• the surface temperature along the length of the rod is rfot necessarily the same but the temperature distribution pat tern is maintained constant.
• This temperature constancy is absolutely critical for providing the stable output laser power with variations, for example, of less than one percent.
• FIG. 3 there is illustrated a typical flow configuration in which the cooling fluid is passed in parallel through the pump cavity 31 and laser rod cooling, tube 37 and is then returned through the exci ⁇ tation: lamp flow tube 35.
• FIGs. 4 and 5 there is illustrated a modified 7 embodiment of the optical laser cavity in which cladding of the laser rod is employed, rather than liminar fluid flow, to maintain the desired constant temperature distribution along the rod.
• cladding of the laser rod is employed, rather than liminar fluid flow, to maintain the desired constant temperature distribution along the rod.
• the entire ellip ⁇ tical cavity 31 is cooled by a fluid such as water and includes a cooling flow tube 35 around the lamp 15 and a sleeve-like cladding 38 around the laser rod 13 with a thin layer of an optically-transparent, thermally- conductive material, such as a static layer of water or a-, silicone gel, interposed between the laser' rod and th cladding.
• the cladding 38 may be constructed of any suitable material such as crystalline quartz or Spinel providing that it is substantially transparent to light from the lamp 15 at the wavelength effective to excite the laser energy states in rod 13, and has appropriate thermal and mechanical properties similar to quartz and Spinel to maintain a stable temperature distribution along the laser rod.
• the cladding sleeve for the laser rod may have a 4 mm inside diameter and a 14 mm outside diameter and be constructed from the material Spinel (MgO:Al2 ⁇ 3).
• spinel MgO:Al2 ⁇ 3
• fluid flows through the elliptical pump cavity 31 around the cladding 38 and is returned through the lamp 15 via flow tube 35.
• Laser Rod - Nd YAG, 4 mm diameter

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Plasma & Fusion (AREA)
• Optics & Photonics (AREA)
• Nonlinear Science (AREA)
• Lasers (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (1)

Family

ID=26669900

Family Applications (1)

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Cited By (5)

Citations (6)

• 1987
  • 1987-04-29 CA CA000535886A patent/CA1281402C/en not_active Expired - Fee Related
  • 1987-04-30 JP JP62502870A patent/JPH01500786A/ja active Pending
  • 1987-04-30 WO PCT/US1987/000983 patent/WO1987006774A1/en unknown
  • 1987-04-30 AU AU73533/87A patent/AU7353387A/en not_active Abandoned
  • 1987-12-30 KR KR1019870701254A patent/KR880701477A/ko not_active Application Discontinuation

Patent Citations (6)

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