US20110051755A1 - Frequency Conversion Laser Head - Google Patents
Frequency Conversion Laser Head Download PDFInfo
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- US20110051755A1 US20110051755A1 US12/943,387 US94338710A US2011051755A1 US 20110051755 A1 US20110051755 A1 US 20110051755A1 US 94338710 A US94338710 A US 94338710A US 2011051755 A1 US2011051755 A1 US 2011051755A1
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- 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
- H01S3/025—Constructional details of solid state lasers, e.g. housings or mountings
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- G—PHYSICS
- G02—OPTICS
- 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
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/353—Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
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- G—PHYSICS
- G02—OPTICS
- 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
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/35—Non-linear optics
- G02F1/37—Non-linear optics for second-harmonic generation
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- 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
- H01S5/00—Semiconductor lasers
- H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
- H01S5/0092—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping for nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
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- 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
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
Definitions
- This invention relates to a laser head with improved heat-diffusing capabilities.
- Frequency converting laser heads are used in numerous fields including, but not limited to industrial and medical applications. Not all wavelength regions of interest are directly accessible with laser. Therefore, it is common to generate visible light by nonlinear conversion of light. Typically a beam of light of a narrow wavelength illuminates a nonlinear component which doubles, triples and etc. the output frequency of the light.
- a laser unit 10 includes a laser module 12 and a frequency conversion laser head 14 .
- the laser module 12 may be configured as a solid state or all fiber laser outputting a pump light at a fundamental frequency.
- the pump is coupled to an output component 16 and delivered to laser head 14 where it impinges upon a frequency conversion component.
- the latter in turn, converts the fundamental frequency of the pump radiation into the desired frequency.
- the output light at the desired frequency is finally delivered to the object to be treated.
- the pump light coupled to laser head 14 , has a power of 10 W.
- the output light delivered to the object to be treated at the desired frequency has a power of about 2 W.
- the other 8 watts of the pump light exiting the non-linear frequency component at the fundamental frequency create a thermally-hazardous situation within laser head 14 , which can possibly lead to a completely unsatisfactory operation of the laser.
- the laser head has a greater volume that renders it space-ineffective. Yet, to the best of the applicant's knowledge, this configuration of the laser head is predominant in the laser industry.
- a laser assembly configured in accordance with the present disclosure and capable of coupling a pump radiation at undesirable frequency out of the case of a frequency conversion laser head.
- the disclosed frequency conversion laser head is configured with a heat dump assembly operative to couple unconverted pump radiation out of the laser head's case.
- the disclosed dump assembly includes an optical filter capable of separating desired frequencies of output light which exits a non-linear conversion element from fundamental, unconverted frequencies.
- the unconverted output light is steered towards and coupled into a dump fiber that guides the output light outside the case of the laser head.
- Evacuating the unconverted light from a laser head allows for a compact structure of the laser head and minimizes detrimental thermal effects on the proper functionality of components of the frequency conversion laser head.
- FIG. 1 is a schematic view of a typical laser assembly including the frequency conversion laser head of the known prior art.
- FIG. 2 is a schematic view of a laser assembly configured in accordance with the present disclosure.
- FIGS. 3A and 3B are respective diagrammatic orthogonal views of different modification of the laser system of FIG. 2 .
- FIG. 4 is a diagrammatic optical schematic of the laser system configured in accordance with the present disclosure.
- FIG. 5 is a view of the laser system of FIG. 3
- FIG. 2 illustrates a diagrammatic view of the disclosed laser assembly 25 including a laser system or pump laser module 18 and a frequency conversion laser head 20 .
- An input component 22 couples a pump light beam Lpump at a fundamental frequency f f to frequency conversion laser head 20 , which is operative to shift the fundamental frequency ff of pump light Lpump to a desired frequency fd.
- the light Lpump is processed inside the case of laser head 20 so that it splits into an output light beam Lout at the desired frequency fd and an output light Lout at the fundamental frequency ff, as explained hereinbelow.
- light Lout at fundamental frequency ff is coupled into a dump fiber 24 guiding light Lout outside frequency conversion laser head 20 .
- the heat generated by the reflected light beam does not accumulate inside the laser head that, thus, does not experience overheating while featuring a compact structure.
- frequency conversion laser head 20 may be configured as a separate component detachably coupled to laser system or pump laser module 18 , or may be manufactured and marketed in combination therewith. In either configuration, frequency conversion laser head 20 may be coupled to system 18 , so that these components are displaceably fixed to one another in a single case ( FIG. 3B ). In accordance with this modification, input and output dump fiber waiveguides 22 and 24 , respectively, are mounted inside laser system 18 .
- frequency conversion laser 20 is configured as a separate component flexibly coupled to system 18 so that these two components are detachably coupled to and displaceable relative to one another.
- laser module 18 and head 20 are coupled by a flexible hollow component 26 ( FIG. 3A ) which houses input fiber 22 and dump fiber 26 .
- FIG. 4 illustrates an optical schematic of disclosed assembly 25 in which frequency conversion laser head 20 is detachably coupled to input fiber waveguide 22 guiding pump light Lpump at fundamental frequency ff from pump 18 .
- the input fiber waveguide 22 outputs the Lpump light beam inside the case of laser head 20 .
- the pump light is guided along a light transmission path (LTP) by well known optical elements, such as a focusing lens 30 coupling the focused pump light to a nonlinear frequency conversion component 32 which is operative to shift the fundamental frequency ff to other desired frequencies fd.
- the light exiting nonlinear component 32 at fundamental and desired frequencies is incident upon a beam splitter 34 locating along the transmission light path.
- beam splitter 34 reflects light beam Lout at fundamental frequency ff along a light dump path (LDP) which extends in a plane transverse to the plane of the transmission light path.
- the light beam Lout at desired frequency fd propagates through beam splitter 34 without deviation from the light transmission path LTP and is coupled by an output focusing optics (not shown) to an output delivery fiber, which is preferably, but not necessarily, a single-mode fiber 40 .
- the beam splitter 34 preferably has at least one reflecting surface covered with dielectric material; as a consequence, beam splitter is transmissive to the entire light beam Lout at the desired frequency except for a small portion thereof which is tapped off for power monitoring purposes, as explained hereinbelow.
- the nonlinear frequency conversion component 32 is based on a non-linear response of the polarization of the material caused by the electric field of the pump light beam.
- the degree of non-linear response is governed by the magnitude of the non-linear susceptibility of the material.
- the effect of this non-linear response is to shift the frequency of the pump light beam to other frequencies.
- Examples of non-linear frequency conversion component 32 includes: second harmonic generation, sum and difference frequency generator, third and higher harmonic generation, stimulated Raman shifting, optical parametric oscillation and others and any combination of these.
- multimode dump fiber 24 terminates inside the housing of system or pump module 18 .
- dump fiber may guide the unconverted light into free space, as illustrated in FIGS. 2 and 4 by dash lines.
- frequency conversion laser head 20 is configured to operate in combination with CW or pulsed laser, which is pumped by pump light Lpump at 1064 and/or 1550 nm and has an average power approaching 20 W.
- the pump light radiation Lpump is launched in nonlinear frequency conversion component 32 configured from a 30 mm long lithium niobate crystal which is periodically poled.
- the crystal is operative to upconvert pump radiation Lpump to 775 nm output light beam Pout carried along the light transmission path with an output power of about 2 W.
- the unconverted pump light Lout at fundamental frequency ff is separated from the second radiation harmonic and further guided outside frequency conversion laser head 20 upon coupling into 100 micron-core MM fiber 24 .
- the dielectric layer deposited on splitters 34 and 36 may be configured to fully reflect not only the light at fundamental frequency, but also a Raman component thereof which has a wavelength different from both, the fundamental and desired wavelengths.
- frequency conversion laser head 20 is provided with a power monitor 28 operative to reliably measure the power of output light beam Lout at desired frequency fd which is carried by output fiber 40 .
- beam splitters 34 and 36 may be configured so that a small portion of output light beam Lout at desired frequency fd is reflected along the light dump path LDP.
- the mirror 36 is transparent for the light at desired frequency fd which propagates through splitter/mirror 36 along a measuring light path (MLP) and is incident on power monitor 28 located downstream from mirror 36 along the measuring light path.
- the power monitor 28 is coupled to a processing unit (not shown) provided with software which is operative to alter the power of pump light beam Lpump, if a measured value deviates from the reference value.
- the laser system/pump module laser 18 may be configured as a solid state laser or a fiber laser and operate in a CW or pulsed regime
- the solid state laser pump 18 may be configured based on, for example, the Nd:YAG laser rod, Al2O3Ti rod, alexandrite rod and many others, well known to one of ordinary skills in the laser art.
- the pulsed operation may include Q-switched operation.
- nonlinear conversion component 32 may include, for example, potassium dihydrogen phosphate (KDP), potassium dideuterium phosphate (KD*P), ammonium dihydrogen phosphate (ADP), potassium titanium oxide phosphate (KTP), rubidium dihydrogen phosphate (RDP), rubidium dihydrogen arcenate (RDA), cesium dihydrogen arsenate (CDA), lithium iodate (LiIO3), lithium niobate (LiNbO3) and others.
- KDP potassium dihydrogen phosphate
- KD*P potassium dideuterium phosphate
- ADP ammonium dihydrogen phosphate
- KTP potassium titanium oxide phosphate
- RDP rubidium dihydrogen phosphate
- RDA rubidium dihydrogen arcenate
- CDA cesium dihydrogen arsenate
- LiIO3 lithium iodate
- LiNbO3 lithium niobate
- laser system 18 is based on a fiber waveguide doped with Er, Yb, Er/Yb, Th and other suitable rare earth elements.
- the fiber laser modules may include a single laser fiber block provided with a resonant cavity. In addition, it may be configured with a single or multiple amplification fiber blocks.
- FIG. 5 illustrated in conjunction with FIG. 4 , illustrates a gain fiber block 50 of pump/laser system 18 based on a multimode (MM) fiber 52 which is pumped by one or more laser diodes (not sown).
- the MM active fiber 52 has a core 54 capable of supporting a fundamental mode at the desired frequency.
- a single mode passive fiber 56 is directly spliced in the end-to-end configuration to MM fiber 52 without the use of a mode converter.
- the core sizes of respective fibers 52 and 56 are chosen so that the fundamental mode spot size of MM fiber 52 substantially matches that of SM fiber 56 so that efficient coupling of the fundamental modes of the fibers is achieved between the fibers at their coupled ends.
- the fiber are so configured that the fundamental mode of MM fiber 52 propagates down its core 54 without significant coupling of power into higher order modes.
- the laser of FIG. 5 forces oscillation in the fundamental mode and actively prevents lasing in the higher order modes in the following way: oscillation of the fundamental mode is forced only by the monomode fiber waveguide and grating 60 which is written into SM fiber 56 .
- the grating partially reflects the fundamental mode signal back into MM fiber 52 such that the reflected fundamental mode signal does not couple to higher order modes.
- the grating 60 in effect, ensures partial reflection of only the fundamental mode, which increases discrimination against higher order modes in MM fiber 52 . Therefore, due to highly predominant fundamental mode oscillation, emission is stimulated in the fundamental mode only.
- the fiber gratings can be replaced with mirrors.
- the system should operate as described by outputting substantially SM pump light beam Lpump at the fundamental frequency ff which is coupled to input SM fiber 22 of FIGS. 3 and 4 .
- the fiber/gain block 50 is illustrated to have a resonant cavity defined between two reflective components, such as mirrors or, preferably, fiber gratings 58 and 60 .
- two reflective components such as mirrors or, preferably, fiber gratings 58 and 60 .
- a single or multiple amplification fiber blocks can be configured identically to fiber block 50 only without the reflective components.
- the laser of FIG. 5 operates by coupling a laser diode light beam to MM fiber 52 .
- the method of coupling may include an end pumping technique and a side pumping technique.
- the MM fiber 52 is, preferably, a large mode area, multi-cladding fiber.
- the laser diode light beam provides a signal at a first wavelength.
- MM fiber 5 is capable of laser action with an emission at the fundamental frequency ff while exhibiting multimode behavior at the fundamental frequency.
- One of the opposite ends of SM fiber 56 which exhibits substantially single mode behavior at the fundamental frequency, is fusion spliced to the opposing end of MM fiber 52 .
- the optical cavity is defined between reflective components 58 and 60 , respectively, and includes at portions of MM and SM fibers. Note that the amplification block would be provided with a MM fiber having its opposite ends spliced to respective SM fibers, wherein the upstream SM fiber would be spliced to SM fiber 56 of block 50 .
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- Nonlinear Science (AREA)
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Abstract
A laser assembly is configured with a frequency conversion laser head operative to shift a fundamental frequency of input light to the desired frequency of an output light. The frequency conversion laser head includes a dump means operative to guide an unconverted output light at the fundamental frequency outside the case of the frequency conversion laser head. The dump means is configured with a guide optics operative to couple the output light at the fundamental frequency to a fiber terminating outside the case of the frequency conversion laser head.
Description
- This application is a continuation of U.S. application Ser. No. 12/152,047 filed with the US Patent and Trademark office on May 12, 2008.
- 1. Field of the Invention
- This invention relates to a laser head with improved heat-diffusing capabilities.
- 2. Prior Art
- Frequency converting laser heads are used in numerous fields including, but not limited to industrial and medical applications. Not all wavelength regions of interest are directly accessible with laser. Therefore, it is common to generate visible light by nonlinear conversion of light. Typically a beam of light of a narrow wavelength illuminates a nonlinear component which doubles, triples and etc. the output frequency of the light.
- In a nonlinear frequency conversion process the efficiency of conversion of laser power at a fundamental frequency into power at combined frequencies, such as the second, third and other harmonic frequencies, is strongly dependent on the intensity of radiation interacting with the non-linear optical material. In practice, high intensities are needed to reach laser output powers up to tens of watts and higher so desirable by the market. The high intensities are accompanied by elevated temperatures which are detrimental to the desired functionality of a laser head explained in detail immediately hereinbelow.
- Referring to
FIG. 1 , alaser unit 10 includes alaser module 12 and a frequencyconversion laser head 14. Thelaser module 12 may be configured as a solid state or all fiber laser outputting a pump light at a fundamental frequency. The pump is coupled to anoutput component 16 and delivered tolaser head 14 where it impinges upon a frequency conversion component. The latter, in turn, converts the fundamental frequency of the pump radiation into the desired frequency. The output light at the desired frequency is finally delivered to the object to be treated. - Not all of the pumped radiation is converted into the desired frequency. In fact, only a small portion of the pumped light is usefully converted; the other, large portion of the pumped radiation remains unchanged and, therefore, useless. For example, the pump light, coupled to
laser head 14, has a power of 10 W. As a result of the frequency conversion, the output light delivered to the object to be treated at the desired frequency has a power of about 2 W. The other 8 watts of the pump light exiting the non-linear frequency component at the fundamental frequency create a thermally-hazardous situation withinlaser head 14, which can possibly lead to a completely unsatisfactory operation of the laser. To somewhat minimize the thermal effect, the laser head has a greater volume that renders it space-ineffective. Yet, to the best of the applicant's knowledge, this configuration of the laser head is predominant in the laser industry. - It is, therefore, desirable to provide a frequency conversion laser head configured to minimize the thermal effect of the unconverted pump radiation.
- It is also desirable to provide a laser assembly configured with the improved frequency conversion laser head, as disclosed immediately above.
- These objectives are attained by a laser assembly configured in accordance with the present disclosure and capable of coupling a pump radiation at undesirable frequency out of the case of a frequency conversion laser head. In particular, the disclosed frequency conversion laser head is configured with a heat dump assembly operative to couple unconverted pump radiation out of the laser head's case.
- Preferably, the disclosed dump assembly includes an optical filter capable of separating desired frequencies of output light which exits a non-linear conversion element from fundamental, unconverted frequencies. The unconverted output light is steered towards and coupled into a dump fiber that guides the output light outside the case of the laser head.
- Evacuating the unconverted light from a laser head allows for a compact structure of the laser head and minimizes detrimental thermal effects on the proper functionality of components of the frequency conversion laser head.
- The above and other features and advantages of the present disclosure will become more readily apparent from a further specific description accompanied by the following drawings, in which:
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FIG. 1 is a schematic view of a typical laser assembly including the frequency conversion laser head of the known prior art. -
FIG. 2 is a schematic view of a laser assembly configured in accordance with the present disclosure. -
FIGS. 3A and 3B are respective diagrammatic orthogonal views of different modification of the laser system ofFIG. 2 . -
FIG. 4 is a diagrammatic optical schematic of the laser system configured in accordance with the present disclosure. -
FIG. 5 is a view of the laser system ofFIG. 3 - Reference will now be made in detail to the disclosed system. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps. The drawings are in simplified form and are far from precise scale. For purposes of convenience and clarity only, the terms “connect,” “couple,” and similar terms with their inflectional morphemes do not necessarily denote direct and immediate connections, but also include connections through mediate elements or devices.
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FIG. 2 illustrates a diagrammatic view of the disclosedlaser assembly 25 including a laser system orpump laser module 18 and a frequencyconversion laser head 20. Aninput component 22 couples a pump light beam Lpump at a fundamental frequency ff to frequencyconversion laser head 20, which is operative to shift the fundamental frequency ff of pump light Lpump to a desired frequency fd. The light Lpump is processed inside the case oflaser head 20 so that it splits into an output light beam Lout at the desired frequency fd and an output light Lout at the fundamental frequency ff, as explained hereinbelow. - In accordance with one aspect of the disclosure, light Lout at fundamental frequency ff is coupled into a
dump fiber 24 guiding light Lout outside frequencyconversion laser head 20. As a consequence and in contrast to the known prior art, the heat generated by the reflected light beam does not accumulate inside the laser head that, thus, does not experience overheating while featuring a compact structure. - Referring to
FIGS. 3A and 3B , frequencyconversion laser head 20 may be configured as a separate component detachably coupled to laser system orpump laser module 18, or may be manufactured and marketed in combination therewith. In either configuration, frequencyconversion laser head 20 may be coupled tosystem 18, so that these components are displaceably fixed to one another in a single case (FIG. 3B ). In accordance with this modification, input and output dump fiber waiveguides 22 and 24, respectively, are mounted insidelaser system 18. Alternatively, as shown inFIG. 3A ,frequency conversion laser 20 is configured as a separate component flexibly coupled tosystem 18 so that these two components are detachably coupled to and displaceable relative to one another. Typically,laser module 18 andhead 20 are coupled by a flexible hollow component 26 (FIG. 3A ) which housesinput fiber 22 anddump fiber 26. -
FIG. 4 illustrates an optical schematic of disclosedassembly 25 in which frequencyconversion laser head 20 is detachably coupled toinput fiber waveguide 22 guiding pump light Lpump at fundamental frequency ff frompump 18. Theinput fiber waveguide 22 outputs the Lpump light beam inside the case oflaser head 20. The pump light is guided along a light transmission path (LTP) by well known optical elements, such as a focusinglens 30 coupling the focused pump light to a nonlinearfrequency conversion component 32 which is operative to shift the fundamental frequency ff to other desired frequencies fd. The light exitingnonlinear component 32 at fundamental and desired frequencies is incident upon a beam splitter 34 locating along the transmission light path. Configured to separate the desired frequency from the fundamental frequency, beam splitter 34 reflects light beam Lout at fundamental frequency ff along a light dump path (LDP) which extends in a plane transverse to the plane of the transmission light path. The light beam Lout at desired frequency fd propagates through beam splitter 34 without deviation from the light transmission path LTP and is coupled by an output focusing optics (not shown) to an output delivery fiber, which is preferably, but not necessarily, a single-mode fiber 40. The beam splitter 34 preferably has at least one reflecting surface covered with dielectric material; as a consequence, beam splitter is transmissive to the entire light beam Lout at the desired frequency except for a small portion thereof which is tapped off for power monitoring purposes, as explained hereinbelow. - The nonlinear
frequency conversion component 32 is based on a non-linear response of the polarization of the material caused by the electric field of the pump light beam. The degree of non-linear response is governed by the magnitude of the non-linear susceptibility of the material. The effect of this non-linear response is to shift the frequency of the pump light beam to other frequencies. Examples of non-linearfrequency conversion component 32 includes: second harmonic generation, sum and difference frequency generator, third and higher harmonic generation, stimulated Raman shifting, optical parametric oscillation and others and any combination of these. - As the output light beam Lout at fundamental frequency ff propagates along the light dump path DLP, it initially impinges upon a
dump mirror 36 which is configured similarly to beam splitter 34 and guides light Lout fundamental frequency ff towards an outputdump focusing lens 38. The latter couples the light beam Lout at fundamental frequency ff tomultimode dump fiber 24 which guides it outside frequencyconversion laser head 20. In accordance with one modification of the present disclosure,multimode dump fiber 24 terminates inside the housing of system orpump module 18. Alternatively, dump fiber may guide the unconverted light into free space, as illustrated inFIGS. 2 and 4 by dash lines. - The desired wavelengths are subject only to a particular configuration of
non-linear conversion component 32. For example, frequencyconversion laser head 20 is configured to operate in combination with CW or pulsed laser, which is pumped by pump light Lpump at 1064 and/or 1550 nm and has an average power approaching 20 W. The pump light radiation Lpump is launched in nonlinearfrequency conversion component 32 configured from a 30 mm long lithium niobate crystal which is periodically poled. The crystal is operative to upconvert pump radiation Lpump to 775 nm output light beam Pout carried along the light transmission path with an output power of about 2 W. The unconverted pump light Lout at fundamental frequency ff is separated from the second radiation harmonic and further guided outside frequencyconversion laser head 20 upon coupling into 100 micron-core MM fiber 24. As readily apparent to one of ordinary skills in the art, the dielectric layer deposited onsplitters 34 and 36 may be configured to fully reflect not only the light at fundamental frequency, but also a Raman component thereof which has a wavelength different from both, the fundamental and desired wavelengths. - In accordance with a further aspect of the disclosure, frequency
conversion laser head 20 is provided with apower monitor 28 operative to reliably measure the power of output light beam Lout at desired frequency fd which is carried byoutput fiber 40. As mentioned above,beam splitters 34 and 36 may be configured so that a small portion of output light beam Lout at desired frequency fd is reflected along the light dump path LDP. Themirror 36 is transparent for the light at desired frequency fd which propagates through splitter/mirror 36 along a measuring light path (MLP) and is incident onpower monitor 28 located downstream frommirror 36 along the measuring light path. The power monitor 28 is coupled to a processing unit (not shown) provided with software which is operative to alter the power of pump light beam Lpump, if a measured value deviates from the reference value. - The laser system/
pump module laser 18, as mentioned above, may be configured as a solid state laser or a fiber laser and operate in a CW or pulsed regime The solidstate laser pump 18 may be configured based on, for example, the Nd:YAG laser rod, Al2O3Ti rod, alexandrite rod and many others, well known to one of ordinary skills in the laser art. The pulsed operation may include Q-switched operation. In conjunction with solid state laser,nonlinear conversion component 32 may include, for example, potassium dihydrogen phosphate (KDP), potassium dideuterium phosphate (KD*P), ammonium dihydrogen phosphate (ADP), potassium titanium oxide phosphate (KTP), rubidium dihydrogen phosphate (RDP), rubidium dihydrogen arcenate (RDA), cesium dihydrogen arsenate (CDA), lithium iodate (LiIO3), lithium niobate (LiNbO3) and others. - Referring to
FIG. 5 ,laser system 18 is based on a fiber waveguide doped with Er, Yb, Er/Yb, Th and other suitable rare earth elements. The fiber laser modules may include a single laser fiber block provided with a resonant cavity. In addition, it may be configured with a single or multiple amplification fiber blocks. -
FIG. 5 , disclosed in conjunction withFIG. 4 , illustrates again fiber block 50 of pump/laser system 18 based on a multimode (MM)fiber 52 which is pumped by one or more laser diodes (not sown). The MMactive fiber 52 has a core 54 capable of supporting a fundamental mode at the desired frequency. To output light pump beam Lout, a single modepassive fiber 56 is directly spliced in the end-to-end configuration toMM fiber 52 without the use of a mode converter. - The core sizes of
respective fibers MM fiber 52 substantially matches that ofSM fiber 56 so that efficient coupling of the fundamental modes of the fibers is achieved between the fibers at their coupled ends. The fiber are so configured that the fundamental mode ofMM fiber 52 propagates down itscore 54 without significant coupling of power into higher order modes. - The laser of
FIG. 5 forces oscillation in the fundamental mode and actively prevents lasing in the higher order modes in the following way: oscillation of the fundamental mode is forced only by the monomode fiber waveguide and grating 60 which is written intoSM fiber 56. The grating partially reflects the fundamental mode signal back intoMM fiber 52 such that the reflected fundamental mode signal does not couple to higher order modes. The grating 60, in effect, ensures partial reflection of only the fundamental mode, which increases discrimination against higher order modes inMM fiber 52. Therefore, due to highly predominant fundamental mode oscillation, emission is stimulated in the fundamental mode only. - As mentioned above, the fiber gratings can be replaced with mirrors. In fact, as long as some form of reflector arrangement with the required reflectivities is present in the system, whether they are internal reflectors written into the waveguides, external reflectors, or a combination of internal and external reflectors, the system should operate as described by outputting substantially SM pump light beam Lpump at the fundamental frequency ff which is coupled to input
SM fiber 22 ofFIGS. 3 and 4 . - The fiber/
gain block 50 is illustrated to have a resonant cavity defined between two reflective components, such as mirrors or, preferably,fiber gratings fiber block 50 only without the reflective components. - The laser of
FIG. 5 operates by coupling a laser diode light beam toMM fiber 52. The method of coupling may include an end pumping technique and a side pumping technique. TheMM fiber 52 is, preferably, a large mode area, multi-cladding fiber. The laser diode light beam provides a signal at a first wavelength. In response, MM fiber 5 is capable of laser action with an emission at the fundamental frequency ff while exhibiting multimode behavior at the fundamental frequency. One of the opposite ends ofSM fiber 56, which exhibits substantially single mode behavior at the fundamental frequency, is fusion spliced to the opposing end ofMM fiber 52. Finally, the optical cavity is defined betweenreflective components SM fiber 56 ofblock 50. - A variety of changes of the disclosed structure may be made without departing from the spirit and essential characteristics thereof. Thus, it is intended that all matter contained in the above description should be interpreted as illustrative only and in a limiting sense, the scope of the disclosure being defined by the appended claims.
Claims (20)
1. A laser assembly comprising a frequency conversion laser head operative to convert a portion of an input light propagating along a transmission light path at a fundamental frequency to a desired frequency of an output light, the frequency conversion laser head having a case, output and dump fibers partially housed in the case and guiding the converted portion at the desired frequency and an unconverted portion of the input light at the fundamental frequency, respectively, outside the case.
2. The laser assembly of claim 1 , wherein the frequency conversion laser head includes a non-linear conversion component housed in the case upstream from the output and dump fibers and operative to transform the portion of the input light at the fundamental frequency to the desired frequency of the light.
3. The laser assembly of claim 2 , wherein the frequency conversion laser head further comprises a beam splitter mounted in the case downstream from the nonlinear conversion component along and impinged upon by the converted and unconverted portions of the input light, the beam splitter being substantially transparent to the converted portion at the desired frequency propagating further along the transmission path but reflecting the unconverted portion of the light at the fundamental frequency along a dump light path, which extends transversely to the transmission path, towards the dump fiber.
4. The laser assembly of claim 3 , wherein the frequency conversion laser head further comprises:
a mirror located downstream from the beam splitter along the dump light path and configured to reflect the unconverted portion at the fundamental frequency towards the dump fiber, and
a dump focusing optics downstream from the mirror and operative to couple the reflected unconverted portion at the fundamental frequency into the dump fiber.
5. The laser assembly of claim 4 , wherein the beam splitter and mirror each are covered with a layer of dielectric material, the beam splitter being configured to tap off a fraction of the converted portion of light at the desired frequency along the light dump path, the minor being transparent to the tapped fraction.
6. The laser assembly of claim 5 further comprising a power monitoring unit housed in the case downstream from the mirror along a measuring light path, which deviates from the light dump path, and operative to measure the tapped fraction of the converted portion of light at the desired frequency so as to determine a power of the converted portion.
7. The laser assembly of claim 1 , the output fiber is a single mode fiber receiving and launching the converted portion of the output light at the desired frequency at an object to be treated outside the ease.
8. The laser assembly of claim 1 further comprising a laser system operative to generate the light at the fundamental frequency which is coupled into the frequency conversion laser head.
9. The laser assembly of claim 8 , wherein the laser system and frequency conversion laser head are displaceably fixed to one another.
10. The laser assembly of claim 8 , wherein the laser system and frequency conversion laser head are displaceable relative to one another.
11. The laser assembly of claim 8 , wherein the laser system is configured as a solid-state laser.
12. The laser assembly of claim 8 , wherein the laser system is configured as an all fiber laser.
13. The laser assembly of claim 12 , wherein the fiber laser includes at least one fiber block configured with:
an active multimode (MM) fiber capable of laser action with an emission at a wavelength having the fundamental frequency; and
a single mode (SM) passive fiber butt-spliced to an output end of the MM fiber and extending towards the laser head, the SM fiber being configured so that the light at the fundamental frequency is coupled into the SM passive fiber substantially without distortion and delivered to the frequency conversion laser head.
14. The laser system of claim 13 further comprising an optical cavity defined between multiple reflectors and including at least parts of the respective MM and SM fibers.
15. The laser system of claim 13 , wherein the SM fiber is directly or indirectly coupled to the frequency conversion laser head.
16. A frequency conversion laser head operative to convert a portion of light propagating along a transmission light path at a fundamental frequency to a desired frequency, the frequency conversion head comprising a case, output and dump fibers partially housed in the case and guiding the converted portion at the desired frequency and an unconverted portion of the input light at the fundamental frequency, respectively, outside the case.
17. The nonlinear conversion laser head of claim 16 further comprising:
a non-linear conversion component housed in the case and operative to convert the portion of the input light at the fundamental frequency to the desired frequency of the output light,
a beam splitter mounted in the case downstream from the nonlinear conversion component along the transmission light path and impinged upon by the light at fundamental and desired frequencies, respectively, the beam splitter being substantially transparent to the light at the desired frequency propagating further along the transmission path but reflecting the light at the fundamental frequency along a dump light path towards the dump fiber.
18. The laser assembly of claim 17 , wherein the frequency conversion laser head further comprises:
a mirror located downstream from the beam splitter along the dump light path and configured to reflect the output light at the fundamental frequency towards the dump fiber, and
a dump focusing optics downstream from the mirror and operative to couple the output light at the fundamental frequency into the dump fiber, wherein the beam splitter and mirror each are covered with a layer of dielectric material, the beam splitter being configured to tap off a fraction of the converted portion of light at the desired frequency along the light dump path, the mirror being transparent to the tapped off portion.
19. The laser assembly of claim 18 further comprising a power monitoring unit housed in the case downstream from the mirror along a measuring light path, which deviates from the light dump path, and operative to measure the tapped off portion of the output light at the desired frequency so as to determine a power of the output light at the desired frequency.
20. A method for operating a laser head comprising:
coupling light at a fundamental frequency into a non-linear element operative to output light at desired and fundamental frequencies, respectively, which are different from one another;
training the output light at a frequency selective element configured to transmit the output light at the desired frequency along a transmission path, and to reflect the output light at the fundamental frequency along a dump path extending transversely to the transmission path;
coupling the transmitted light at the desired frequency into a one fiber located in a case of the laser head and the reflected light at the fundamental frequency into a dump fiber spaced from the one fiber within the case, thereby guiding the light at the desired and fundamental frequencies outside the case.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US12/943,387 US20110051755A1 (en) | 2008-05-12 | 2010-11-10 | Frequency Conversion Laser Head |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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US12/152,047 US8179934B2 (en) | 2008-05-12 | 2008-05-12 | Frequency conversion laser head |
US12/943,387 US20110051755A1 (en) | 2008-05-12 | 2010-11-10 | Frequency Conversion Laser Head |
Related Parent Applications (1)
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US12/152,047 Continuation US8179934B2 (en) | 2008-05-12 | 2008-05-12 | Frequency conversion laser head |
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US20110051755A1 true US20110051755A1 (en) | 2011-03-03 |
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US12/152,047 Active 2030-02-25 US8179934B2 (en) | 2008-05-12 | 2008-05-12 | Frequency conversion laser head |
US12/943,387 Abandoned US20110051755A1 (en) | 2008-05-12 | 2010-11-10 | Frequency Conversion Laser Head |
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JP5024088B2 (en) * | 2008-02-05 | 2012-09-12 | セイコーエプソン株式会社 | Laser light source device, illumination device, image display device, and monitor device |
US8179934B2 (en) * | 2008-05-12 | 2012-05-15 | Ipg Photonics Corporation | Frequency conversion laser head |
US9477041B2 (en) | 2010-07-30 | 2016-10-25 | Kla-Tencor Corporation | Low stray light beam dump with fiber delivery |
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US20090279574A1 (en) | 2009-11-12 |
US8179934B2 (en) | 2012-05-15 |
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