CN113346339A - Large-energy cavity emptying Yb femtosecond laser - Google Patents
Large-energy cavity emptying Yb femtosecond laser Download PDFInfo
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- 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
- H01S3/0619—Coatings, e.g. AR, HR, passivation layer
- H01S3/0621—Coatings on the end-faces, e.g. input/output surfaces of the laser light
- H01S3/0623—Antireflective [AR]
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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
- H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
- H01S3/08—Construction or shape of optical resonators or components thereof
- H01S3/081—Construction or shape of optical resonators or components thereof comprising three or more reflectors
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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
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/094049—Guiding of the pump light
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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
- H01S3/09—Processes or apparatus for excitation, e.g. pumping
- H01S3/091—Processes or apparatus for excitation, e.g. pumping using optical pumping
- H01S3/094—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light
- H01S3/0941—Processes or apparatus for excitation, e.g. pumping using optical pumping by coherent light of a laser diode
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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
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10053—Phase control
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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
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/11—Mode locking; Q-switching; Other giant-pulse techniques, e.g. cavity dumping
- H01S3/1106—Mode locking
- H01S3/1112—Passive mode locking
Abstract
The invention belongs to the technical field of femtosecond laser, and discloses a large-energy cavity emptying Yb femtosecond laser, which comprises: the device comprises a pumping source, an optical coupling system, a plane dichroic mirror, a Yb laser crystal, a first concave mirror, a second concave mirror, an output mirror, a first GTI mirror, a second GTI mirror, a third concave mirror, a nonlinear medium, a fourth concave mirror, a TFP, an electro-optic modulator and a plane reflecting mirror. The cavity emptying laser is based on a high-power Kerr lens mode locking oscillator, does not need to start mode locking by means of a fragile SESAM device, and ensures that intra-cavity mode locking pulses have shorter pulse width and higher single pulse energy; after the large-energy short-pulse-width pulse in the cavity is stably oscillated, the polarization state of the laser is changed by using an electro-optical modulator, and the pulse laser with the pulse width of less than 100 fs and the pulse width of more than 0.5 muJ can be effectively derived and realized by combining with the TFP.
Description
Technical Field
The invention belongs to the technical field of femtosecond lasers, and particularly relates to a large-energy cavity emptying Yb femtosecond laser.
Background
At present: the large-energy femtosecond laser is widely applied to the fields of advanced scientific research and industrial processing, however, the laser single pulse energy directly output by the femtosecond oscillator is generally in the order of several nanometers (nJ) or tens of nJ, and cannot meet the requirements of femtosecond filamentation, generation of higher harmonics and micromachining of materials. The cavity emptying femtosecond laser is a laser which is based on the cavity emptying technology and realizes the direct expansion of the single pulse energy output by an oscillator. Compared with a laser amplifier, the structure is more compact and the cost is lower.
A kerr lens based mode locked (KLM) titanium sapphire oscillator is one of the solutions for cavity-emptying lasers. In 1993, M. Ramaswamy on Opt. Lett 18, pp. 1822-1824 reports that the cavity-emptying femtosecond laser outputs a single pulse with the energy of 100 nJ, the pulse width of 50 femtoseconds (fs) and the repetition frequency of 950 kHz. Maxim S. Pshenichnikov on Opt. Lett 19, pp. 572-574 of 1994 realized 10 fs magnitude cavity emptying output, with single pulse energy of 60 nJ and repetition frequency of 200 kHz. The early cavity-emptying femtosecond laser based on the titanium sapphire crystal of KLM has the advantage of narrow pulse width, but the single pulse energy output by the cavity-emptying laser cannot reach hundreds of nJ or even micro-focus (mu J) level due to the problem that the average power in the cavity of the Kerr lens mode locking technology is limited at that time. And because of the inherent problem of overhigh pumping cost of the titanium sapphire system, the cavity emptying laser turns to an ytterbium (Yb) doped oscillator based on semiconductor compatible absorption mirror (SESAM) mode locking.
The SESAM mode-locked Yb oscillator can be directly pumped by a high-power LD, and the sufficient emptying power and single pulse energy in the cavity are guaranteed. In 2004, the LD pumped SESAM mode-locked Yb: glass cavity-dumped laser (A. Killi et al Proceedings of SPIE Vol. 5460) was first realized, and single-pulse energy of 400 nJ was obtained, with corresponding pulse widths and repetition frequencies of 520 fs and 200 kHz, respectively. The output single pulse energy of the cavity-emptying laser is improved to the mu J order by using a single or a plurality of Yb: KYW crystals (Palmer G et al Opt Express 15, 16017-. Although the cavity emptying lasers can output high single pulse energy, the pulse width output by the cavity emptying lasers is hundreds of femtoseconds, and the service life of the key starting mode locking device SESAM in the cavity is easy to reduce under high heat load caused by high power, even damage can occur, and the long-time stable work of the lasers is not facilitated.
Through the above analysis, the problems and defects of the prior art are as follows: the existing cavity emptying laser with a gain medium being a titanium gem based on KLM or Yb mode-locked by SESAM cannot simultaneously obtain femtosecond laser output with short pulse width, large energy, long service life and low cost. Therefore, how to establish a cavity emptying laser integrating the advantages becomes a problem to be solved urgently.
The difficulty in solving the above problems and defects is: in the current various cavity-emptying femtosecond lasers, the cavity-emptying femtosecond laser using the SESAM mode locking can not realize the femtosecond laser output with short pulse width, and the damage of key mode locking devices is very likely to be caused in the laser operation process, and the key mode locking devices need to be maintained or replaced regularly; the cavity-emptying femtosecond laser utilizing the traditional KLM mode locking cannot use a high-power LD as a pumping source, so that the output energy of the cavity-emptying femtosecond laser is too low. Solving the above problems has certain device process and cavity design difficulties.
The significance of solving the problems and the defects is as follows: the mode locking mode of SESAM is abandoned, the cavity-emptying femtosecond laser for KLM mode locking is designed again to solve the problems, the output of the femtosecond laser with short pulse width and high energy is realized, the cost of the laser is lower, and the service life and the maintenance-free time are longer, so that the application requirements in the fields of advanced scientific research and micro-nano processing are met.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a large-energy cavity emptying Yb femtosecond laser, a control method and application.
The invention is thus realized, a large-energy cavity-dumped Yb femtosecond laser, comprising:
the laser cavity is formed by a pumping source 1 and an optical coupling system 2. The pump laser emitted by the pump source is focused by the optical coupling system and passes through the plane dichroic mirror 3 to the Yb laser crystal 4.
Laser in the laser cavity starts from a plane dichroic mirror 3 and passes through a vertically arranged Yb laser crystal 4 from right to left; then the laser passes through a first concave mirror 5, a first GTI mirror 8, a second GTI mirror 9, a third GTI mirror 10 and a third concave mirror 11 in sequence; the laser then passes from left to right through a nonlinear medium 12 placed at the brewster angle; then the laser passes through a fourth concave mirror 13, a TFP sheet 14, an electro-optical modulator 15 and a plane reflector 16 in sequence; the laser is vertically reflected by the plane reflector 16 and returns to the plane dichroic mirror 3 in the original path in the front transmission direction; then the laser is transmitted to the second concave mirror 6 by the dichroic mirror 3 and is transmitted to the output mirror 7 by the second concave mirror 6; finally, the laser is vertically reflected by the light source 7, the laser returns to the light source 16, and then the laser oscillates back and forth along the whole path.
Further, the pump source outputs pump laser with the wavelength of 976nm or 980 nm, the output power is not less than 50W, the fiber core diameter is 105 micrometers, the numerical aperture is 0.15, and the proportion of the optical coupling system is 1: 0.8. The parameters can ensure that the laser crystal can have better pumping absorption rate and laser conversion rate.
Further, the Yb laser crystal is vertically placed, and both surfaces of the Yb laser crystal are plated with anti-reflection films of 980-fold 1100 nm and are placed on a water-cooling copper block. This is beneficial to reduce the extra loss caused by the crystal surface to the laser and also beneficial to relieve the heat effect on the crystal.
Further, the first GTI mirror, the second GTI mirror and the third GTI mirror are configured to provide sufficient anomalous dispersion that has a total amount of negative dispersion sufficient to compensate for the positive dispersion introduced by the gain crystal, the kerr medium, the electro-optic modulator and the polarization beam splitter. Normal dispersion introduced by air in the cavity and the laser crystal can be effectively compensated, and self-phase modulation is balanced;
furthermore, the nonlinear medium is calcium fluoride, the thickness of the nonlinear medium is 1-2 mm, and the nonlinear medium is not coated with films on two surfaces and placed at the Brewster angle. The calcium fluoride material can effectively relieve the pulse splitting phenomenon caused by excessively high nonlinear phase shift, and can also relieve the multi-photon absorption effect. In addition, the scheme that the Kerr medium is placed at the Brewster angle can compensate the astigmatism effect on one hand and can ensure the polarization degree of the laser in the cavity on the other hand.
Further, the reflectivity R of the plane mirror is more than 99.9%. The high reflectivity of the mirror reduces the intra-cavity losses.
Further, the maximum repetition frequency of the electro-optical modulator is not less than 1 MHz.
Furthermore, the output mirror is a plane mirror, one surface facing the resonant cavity is plated with a dielectric film with 20% of output coupling rate at the position of the oscillating laser, the other surface is plated with an anti-reflection dielectric film for the oscillating laser, and T is more than 99.8%. The output mirror with the parameters can effectively inhibit the direct current phenomenon in the mode locking pulse.
Another object of the present invention is to provide a control method for the large-energy cavity dumping Yb femtosecond laser, the control method comprising: pump light emitted from the LD is incident to the Yb gain crystal after passing through the collimating focusing mirror; the electro-optical modulator is firstly in an unpressurized state, laser forms self-reproduction stable oscillation, and then passes through the first concave mirror, the first GTI mirror, the second GTI mirror, the third concave mirror, the nonlinear crystal, the fourth concave mirror, the TFP, the electro-optical modulator, the end mirror and the output mirror in sequence along the original path; when the electro-optical modulator is in a pressurized state, laser starts from the end mirror, changes from p polarization to s polarization after passing through the electro-optical modulator, is finally led out of the cavity through the TFP, then the pressurization on the electro-optical modulator is cancelled, residual seed laser in the cavity is continuously amplified through the gain crystal according to a running track without pressurization until gain and loss in the cavity are balanced, and the laser reaches a new stable running state, so that large-energy pulses in the cavity can be periodically poured out by periodically applying proper voltage to the electro-optical modulator.
It is another object of the present invention to provide a femtosecond oscillator that uses the large-energy cavity dumped Yb femtosecond laser.
By combining all the technical schemes, the invention has the advantages and positive effects that: the cavity emptying laser is based on a high-power Kerr lens mode locking oscillator, does not need to start mode locking by means of a fragile SESAM device, and ensures that intra-cavity mode locking pulses have shorter pulse width and higher single pulse energy. After the large-energy short-pulse-width pulse in the cavity is stably oscillated, the polarization state of the laser is changed by using an electro-optical modulator, and the pulse laser with the pulse width of less than 100 fs and the pulse width of more than 0.5 muJ can be effectively derived and realized by combining with the TFP.
The invention provides a cavity emptying femtosecond laser based on a high-power ytterbium-doped Kerr lens mode-locked oscillator for the first time, and compared with the traditional cavity emptying femtosecond laser, the cavity emptying femtosecond laser can generate femtosecond laser with high energy, short pulse, stable work and low price. Can be widely applied to the fields of advanced scientific research, industrial processing and the like, and has good application prospect and commercial value.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed to be used in the embodiments of the present application will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present application, and it is obvious for those skilled in the art that other drawings can be obtained from the drawings without creative efforts.
FIG. 1 is a diagram of a large energy cavity dumping Yb femtosecond laser provided by an embodiment of the present invention FIG. 1 is a diagram of an optical path of a large energy cavity dumping femtosecond laser proposed by the present invention;
in fig. 1: 1. a pump source; 2. an optical coupling system; 3. a planar dichroic mirror; 4. a Yb laser crystal; 5. a first concave mirror; 6. a second concave mirror; 7. an output mirror; 8. a first GTI mirror; 9. a second GTI mirror; 10. a third GTI mirror; 11. a third concave mirror; 12. a non-linear medium; 13. a fourth concave mirror; 14. TFP; 15. an electro-optic modulator; 16. a plane mirror.
Fig. 2 is a schematic diagram of the stability of the output average power of a large-energy cavity-dumped femtosecond laser in non-dumping state (without an electro-optical modulator inserted).
Fig. 3 is a schematic diagram of the output pulse width of a large-energy cavity-dumped femtosecond laser without dumping (without inserting an electro-optical modulator) according to the invention.
Fig. 4 is a schematic diagram of mode-locked fundamental frequency spectrum of a large-energy cavity-dumping femtosecond laser without dumping (without an electro-optical modulator inserted).
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Aiming at the problems in the prior art, the invention provides a large-energy cavity emptying Yb femtosecond laser, a control method and application thereof, and the invention is described in detail below with reference to the attached drawings.
As shown in fig. 1, a large-energy cavity emptying femtosecond laser provided by the embodiment of the present invention includes:
the pumping source 1 is a semiconductor laser coupled and output by optical fiber and used for outputting pumping laser with the wavelength of 976nm or 980 nm, the output power is not less than 50W, the core diameter of the optical fiber is 105 micrometers, and the numerical aperture is 0.15.
The laser cavity is formed by a pumping source 1 and an optical coupling system 2. The pump laser emitted by the pump source is focused by the optical coupling system and passes through the plane dichroic mirror 3 to the Yb laser crystal 4.
Laser in the laser cavity starts from a plane dichroic mirror 3 and passes through a vertically arranged Yb laser crystal 4 from right to left; then the laser passes through a first concave mirror 5, a first GTI mirror 8, a second GTI mirror 9, a third GTI mirror 10 and a third concave mirror 11 in sequence; the laser then passes from left to right through a nonlinear medium 12 placed at the brewster angle; then the laser passes through a fourth concave mirror 13, a TFP sheet 14, an electro-optical modulator 15 and a plane reflector 16 in sequence; the laser is vertically reflected by the plane reflector 16 and returns to the plane dichroic mirror 3 in the original path in the front transmission direction; then the laser is transmitted to the second concave mirror 6 by the dichroic mirror 3 and is transmitted to the output mirror 7 by the second concave mirror 6; finally, the laser is vertically reflected by the light source 7, the laser returns to the light source 16, and then the laser oscillates back and forth along the whole path.
The optical coupling system 2 is characterized in that the output of the optical fiber passes through a 1: the 0.8 optical coupling system is focused.
And the plane dichroic mirror 3 is used for coupling the pump light into the cavity.
The Yb laser crystal 4 is vertically arranged, both surfaces of the Yb laser crystal are coated with anti-reflection films of 980 and 1100 nm, and the Yb laser crystal is arranged on a water-cooling copper block.
The first concave mirror 5, the second concave mirror 6, the third concave mirror 11 and the fourth concave mirror 13 are used for controlling the size of a laser mode in the gain crystal and the nonlinear medium so as to meet the matching of pump light and provide a sufficient nonlinear Kerr effect.
A first GTI mirror 8, a second GTI mirror 9 and a third GTI mirror 10 for providing-2900 fs2While balancing the self-phase modulation, the total amount of negative dispersion is sufficient to compensate for the positive dispersion introduced by the gain crystal, kerr medium, electro-optic modulator and polarization beam splitter.
The nonlinear medium 12 is calcium fluoride with a diameter of half an inch, the thickness of the nonlinear medium is 1-2 mm, two surfaces of the nonlinear medium are not coated with films, and the nonlinear medium is placed at a Brewster angle and used for introducing a Kerr effect.
The plane reflector 16 has a reflectivity R of 99.9%.
The output mirror 7 is a plane mirror, one surface facing the resonant cavity is plated with a dielectric film with 20% of output coupling ratio at the position of the oscillation laser, and the other surface is plated with an anti-reflection dielectric film (T >99.8%) for the oscillation laser.
The electro-optical modulator 15, the maximum repetition frequency is not less than 1 MHz, is used for changing the polarization state of passing the laser in the cavity;
a TFP 14 for deriving the dump laser;
the laser operation track in the invention is as follows: pump light emitted from the LD is incident to the Yb gain crystal after passing through the collimating focusing mirror; the electro-optical modulator is firstly in an unpressurized state, laser forms self-reproduction stable oscillation, and then passes through the first concave mirror, the first GTI mirror, the second GTI mirror, the third concave mirror, the nonlinear crystal, the fourth concave mirror, the TFP, the electro-optical modulator, the end mirror and then returns to the dichroic mirror, the second concave mirror and the output mirror along the original path. When the electro-optical modulator is in a pressurized state, laser starts from the end mirror, changes from p polarization to s polarization after passing through the electro-optical modulator, is finally led out of the cavity through the TFP, then the pressurization on the electro-optical modulator is cancelled, residual seed laser in the cavity is continuously amplified through the gain crystal according to a running track without pressurization until gain and loss in the cavity are balanced, and the laser reaches a new stable running state, so that large-energy pulses in the cavity can be periodically poured out by periodically applying proper voltage to the electro-optical modulator.
The present invention uses the soft-aperture stop effect to initiate kerr lens mode locking. Compared with a hard diaphragm, no solid small hole is inserted into the cavity, so that smaller loss in the cavity can be ensured, higher power in the cavity can be obtained, and a foundation is laid for further improving cavity emptying energy.
The invention controls the relative distance of the concave mirrors 11 and 12, so that the mode-locked laser works at the edge of the lower stable region, and the mode-locked laser has higher Kerr sensitivity and can ensure the startup and long-time stability of mode locking. Therefore, in the process of operating the cavity emptying laser, the mode locking state cannot be interrupted by external fluctuation.
The large-energy cavity emptying mechanism is formed by combining the electro-optic modulator and the TFP, and the cavity emptying can be realized by using the electro-optic modulator in a specific embodiment.
The nonlinear medium in the scheme is made of calcium fluoride material, and in a specific embodiment, the material of the nonlinear medium can be white gem, fused silica and the like according to the accumulation amount of nonlinear phase shift in the cavity.
The transmittance of the output mirror in the scheme is 20%, and in a specific embodiment, the output mirror selects one of the transmittance ranges from 10% to 40% according to the difference of single pulse energy in an actual cavity and the direct current condition.
Compared with the traditional cavity-emptying femtosecond laser, the invention can generate the femtosecond laser with high energy, short pulse, stable work and low cost. Can be widely applied to the fields of advanced scientific research, industrial processing and the like, and has good application prospect and commercial value.
When no TFP and electro-optical modulator exist in the cavity, the invention can stably output the pulse laser with the average power of more than 10W (10.4W, figure 2) and the pulse width of less than 100 fs (98 fs, figure 3). At a repetition frequency of 81 MHz (fig. 4), the corresponding intracavity single pulse energy has reached 0.6 muj. The above data illustrate that this inventive scheme can support the production of large energy pulsed lasers at 0.5 muJ, sub-100 fs.
When the cavity of the invention is not provided with the TFP and the electro-optical modulator, the output power of the pulse laser is very stable (RMS <0.35% @1 h, figure 2), and the radio frequency signal-to-noise ratio of the laser is also higher (56 dB, figure 3). The experimental results indicate that the cavity emptying femtosecond laser based on the KLM oscillator has stronger reliability.
In the description of the present invention, "a plurality" means two or more unless otherwise specified; the terms "upper", "lower", "left", "right", "inner", "outer", "front", "rear", "head", "tail", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the invention. Furthermore, the terms "first," "second," "third," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. A large-energy cavity dumping Yb femtosecond laser, comprising:
the pumping source is a semiconductor laser coupled and output by an optical fiber and is used for outputting pumping laser;
the optical coupling system is used for focusing the output optical fiber through the optical coupling system;
the planar dichroic mirror is used for coupling the pump light into the cavity;
a Yb laser crystal is vertically arranged, and both surfaces of the Yb laser crystal are plated with anti-reflection films and are arranged on a water-cooling copper block;
the first concave mirror, the second concave mirror, the third concave mirror and the fourth concave mirror are used for controlling the size of a laser mode in the gain crystal and the nonlinear medium, and the matching of pump light and the provision of a sufficient nonlinear Kerr effect are met;
the first GTI mirror, the second GTI mirror and the third GTI mirror are used for providing enough anomalous dispersion to compensate normal dispersion introduced by air in the cavity and the laser crystal and balance self-phase modulation;
the nonlinear medium is calcium fluoride, two surfaces of the nonlinear medium are not coated with films, and the nonlinear medium is placed at a Brewster angle and used for introducing a Kerr effect;
a plane mirror to which reflected laser light is applied;
an output mirror for applying the oscillation laser light coupled at an output;
the electro-optical modulator is used for changing the polarization state of the laser passing through the cavity;
a TFP for leading out the dump laser;
the outside of the laser cavity is composed of a pumping source and an optical coupling system, and pumping laser emitted by the pumping source is focused by the optical coupling system and is positioned on the Yb laser crystal through the plane dichroic mirror; laser in the laser cavity starts from a plane dichroic mirror firstly and passes through a vertically arranged Yb laser crystal from right to left; then the laser passes through the first concave mirror, the first GTI mirror, the second GTI mirror, the third GTI mirror and the third concave mirror in sequence; the laser then passes from left to right through a nonlinear medium placed at the Brewster angle; then the laser passes through a fourth concave mirror, a TFP sheet, an electro-optic modulator and a plane reflector in sequence; the laser is vertically reflected by the plane reflector and returns to the plane dichroic mirror along the original path in the front transmission direction; then the laser is transmitted to the second concave mirror by the dichroic mirror and is transmitted to the output mirror by the second concave mirror; finally, the laser is reflected vertically, the laser returns to the upper part in the original path, and then the laser oscillates back and forth continuously according to the whole path.
2. The large-energy cavity-dumped Yb femtosecond laser as set forth in claim 1, wherein the pump source outputs pump laser light with a wavelength of 976nm or 980 nm, an output power is not less than 50W, a fiber core diameter is 105 μm, and a numerical aperture is 0.15.
3. The large-energy cavity-dumped Yb femtosecond laser according to claim 1, wherein an optical fiber of the optical coupling system is focused by the optical coupling system after being output.
4. The large-energy cavity emptying Yb femtosecond laser as claimed in claim 1, wherein the Yb laser crystal is vertically arranged, both sides are coated with anti-reflection films of 980 and 1100 nm, and the crystal is arranged on a water-cooled copper block.
5. The large energy cavity dumping Yb femtosecond laser as claimed in claim 1, wherein said first GTI mirror, second GTI mirror and third GTI mirror are configured to provide anomalous dispersion with a total amount of negative dispersion sufficient to compensate for positive dispersion introduced by the gain crystal, kerr medium, electro-optic modulator and polarization beam splitter. .
6. The large-energy cavity-pumped Yb femtosecond laser according to claim 1, wherein the nonlinear medium is calcium fluoride and has a thickness of 1-2 mm.
7. The large-energy cavity-dumped Yb femtosecond laser according to claim 1, wherein the maximum repetition rate of the electro-optical modulator is not less than 1 MHz. .
8. The Yb femtosecond laser as claimed in claim 1, wherein the output mirror is a flat mirror, one surface facing the inside of the cavity is coated with a dielectric film with 20% output coupling ratio at the position of the oscillation laser, and the other surface is coated with an antireflection dielectric film for the oscillation laser.
9. A control method of a large-energy cavity dumping Yb femtosecond laser as claimed in any one of claims 1 to 8, wherein the control method comprises: pump light emitted from the LD is incident to the Yb gain crystal after passing through the collimating focusing mirror; the electro-optical modulator is firstly in an unpressurized state, laser forms self-reproduction stable oscillation, and then passes through the first concave mirror, the first GTI mirror, the second GTI mirror, the third concave mirror, the nonlinear crystal, the fourth concave mirror, the TFP, the electro-optical modulator, the end mirror and the output mirror in sequence along the original path; when the electro-optical modulator is in a pressurized state, laser starts from an end mirror, changes from p polarization to s polarization after passing through the electro-optical modulator, is finally led out of the cavity through a TFP (pulse width modulation), then the pressurization on the electro-optical modulator is cancelled, residual seed laser in the cavity is continuously amplified through a gain crystal according to a running track when the laser is not pressurized until the gain and the loss in the cavity are balanced, the laser reaches a new stable running state, and large-energy pulses in the cavity can be periodically poured out by periodically applying proper voltage to the electro-optical modulator.
10. A femtosecond oscillator, wherein the femtosecond oscillator uses a large-energy cavity-dumping Yb femtosecond laser as set forth in any one of claims 1 to 8.
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| US11552442B2 (en) * | 2018-01-25 | 2023-01-10 | Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften E.V. | Device and method for generating laser pulses by Kerr lens based mode locking with a loss-modulation device as a Kerr medium |
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