CN114156727A - High-power intermediate infrared tunable femtosecond laser generating device - Google Patents
High-power intermediate infrared tunable femtosecond laser generating device Download PDFInfo
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- 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
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- 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
- H01S3/1083—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 using parametric generation
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- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
- H01S3/0092—Nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
Abstract
The invention belongs to the technical field of infrared femtosecond laser, and discloses a high-power intermediate infrared tunable femtosecond laser generating device, which comprises: the pumping module is used for pumping the OPO optical parametric oscillation module; an Optical Parametric Oscillation (OPO) module for converting input laser light (pump light) into two output light (signal light and idler light) having lower frequencies; and the Difference Frequency Generation (DFG) module is used for carrying out difference frequency on the two beams of laser generated by the OPO module to generate high-power mid-infrared tunable femtosecond laser. According to the method, the high-power mid-infrared tunable femtosecond laser is obtained by combining OPO + DFG, the tunable signal light and the idler frequency light are generated by utilizing the high-power femtosecond oscillator pump OPO, and the high-power femtosecond laser is obtained by respectively taking the high-power femtosecond oscillator pump OPO as the difference frequency to generate the required pump light and signal light to inject into the mid-infrared nonlinear crystal, so that the output mid-infrared femtosecond laser has the characteristics of high power and tunable.
Description
Technical Field
The invention belongs to the technical field of infrared femtosecond lasers, and particularly relates to a high-power intermediate infrared tunable femtosecond laser generation device.
Background
At present: the mid-infrared is located in a spectral wavelength range of 3-20 μm, wherein the absorption characteristic of 3-5 μm mid-infrared laser in atmospheric molecules makes the laser in the band have important application value in the fields of military affairs, medical treatment, remote sensing, communication, industrial processing and the like, and in recent years, many research works are developed around the mid-infrared laser. Furthermore, the mid-infrared ultrashort pulse laser can reach femtosecond magnitude due to extremely short pulse width, and has the advantage of extremely high pulse peak power after amplification, so that the requirements of various applications such as free space optical communication, trace gas detection, environmental monitoring, biomedicine and the like on a light source can be met. Therefore, the method has very important value for researching the mid-infrared femtosecond laser with the characteristics of wide tuning, high power and the like.
Resonant cavity mode locking technology is usually adopted for realizing ultrashort pulse laser output in visible and near infrared wave bands, but due to the lack of a proper laser gain medium, the output light tuning range is narrow, and the output light tuning range is difficult to be directly applied to a middle infrared region. Therefore, a high-power femtosecond laser is adopted to obtain a high-power intermediate infrared femtosecond laser with a wide wavelength tuning range by utilizing a nonlinear frequency conversion technology. The generation of ultra-short mid-infrared laser pulses primarily utilizes nonlinear frequency conversion techniques to down-convert the visible ultra-short pulse frequency to the mid-infrared region, such as Optical Parametric Oscillation (OPO) and Difference Frequency Generation (DFG). The OPO method originated in the early 60 s of the 20 th century and was excited by a laser (pump light) in a nonlinear medium to generate two laser (signal light and idler light) outputs. The OPO has the characteristics of simple structure, large tuning range, and operation modes such as pulse, continuous mode locking and the like. The laser with wide wavelength tuning range can be obtained by adopting different resonant cavities, nonlinear crystals and pumping light wavelengths, and has the advantages of high repetition frequency, high conversion efficiency, full curing and the like. The DFG method is characterized in that two beams of laser (pump light and signal light) are excited in a nonlinear medium to generate a beam of laser (idler frequency light) for output, a resonant cavity is not needed in the frequency conversion process, and the laser passes through a nonlinear crystal once, so that the DFG method has the comprehensive advantages of no threshold limit, no complex cavity adjustment, wide output laser tuning range, high efficiency and the like.
The current mature high-power femtosecond laser is a Kerr lens mode-locked laser based on titanium-doped sapphire and a Kerr lens mode-locked laser based on ytterbium (Yb) doping3+) The gain medium all-solid-state femtosecond laser and the titanium sapphire laser are limited by the existing pumping source power and the quantum efficiency of the crystal, so that the average power output from the mode-locked oscillator is low. In contrast, the ytterbium-doped femtosecond laser has higher power and a good light source, and has greater advantages for the output requiring high average power and narrow pulses. It is considered that a high-power femtosecond laser is adopted to directly pump the OPO to generate the femtosecond laser, or the pump source laser is divided into two beams to be output, wherein one beam is subjected to spectrum broadening and then is subjected to difference frequency with the other beam to generate the femtosecond laser. However, both of these methods require a nonlinear crystal highly transparent to 1 μm pump light, and if the conventional crystal is highly transparent to 1 μm, the wavelength of the long wavelength generated by multiphoton absorption is limited to 4 to 5 μm, and thus it is impossible to directly generate high-power laser light having a longer wavelength. If AgGaS is used2、AgGaSe2、cdSiP2、ZnGeP2The equibirefringent crystal can generate laser with wavelength of 5 μm or more, but the nonlinear coefficient and quality factor of the former two are low, and the crystal CbSiP with high quality factor and large nonlinear coefficient2The light transmission range of the laser is small (0.65-7 mu m), so that the high-power mid-infrared long-wave femtosecond laser cannot be obtained under the influence of crystal properties.
ZnGeP2The crystal has a series of advantages of large nonlinear coefficient, high quality factor, high thermal conductivity, large damage threshold and the like, and meanwhile, the crystal has wide light transmission range, and is an excellent nonlinear optical crystal material capable of generating high-power tunable intermediate infrared output through a DFG process. However, a key problem with the ZGP crystal is that it is opaque in the sub-2 μm band and cannot be pumped by high power 1 μm near-infrared laser, and it is currently preferred to have its absorption at 1.6 μm at a minimum of 0.08cm-1. Therefore, the OPO technology can be used for converting the 1 μm pump source laser to generate two beams of femtosecond lasers with longer wavelengths of 1.7 μm and 2.6 μm, the wavelength range of the femtosecond lasers can be tuned, and then the ZGP crystal with excellent optical property is used for difference frequencyGenerates high-power mid-infrared tunable femtosecond laser with the wavelength tuning range of 4-9 μm. The difference frequency through multiple nonlinear processes has the greatest advantage that the conversion efficiency can be improved by utilizing the near infrared signal light and idler frequency light generated by OPO to remove the difference frequency, the generated femtosecond mid-infrared laser pulse has the advantages of wide tuning range and high repetition frequency, and the output mid-infrared femtosecond optical power can be improved by increasing the power of initial pump light. The Optical Parametric Oscillation (OPO) can realize the output of continuously tunable wavelength in a wider frequency spectrum range, and meanwhile, a difference frequency method (DFG) is adopted to obtain ultrashort mid-infrared pulses, so that the laser has the advantages of good beam quality, no need of a resonant cavity and the like, can finally obtain high-power wide-tuning mid-infrared laser output, has good stability of output laser, and can be widely applied to the fields of air pollution detection, remote sensing, spectral analysis, military and the like.
Through the above analysis, the problems and defects of the prior art are as follows: the prior art for generating the mid-infrared femtosecond laser at present has low output power, narrow tuning range and high requirement on nonlinear crystal.
The difficulty in solving the above problems and defects is: on the other hand, if a nonlinear crystal is required to be highly pumped by a1 μm high-power ytterbium-doped femtosecond laser, if the conventional crystal is highly transparent to 1 μm, the long-wavelength generated by multiphoton absorption is limited to 4-5 μm, and high-power laser with longer wavelength cannot be directly generated, but the ZGP crystal which can generate long-wavelength and medium-infrared output and has extremely excellent optical properties is opaque in a wavelength band below 2 μm and cannot be directly pumped by the 1 μm laser. Therefore, the 1 μm pump source laser needs to be converted into two beams of laser with longer wavelength, and then the high-power mid-infrared tunable femtosecond laser is generated by difference frequency by using the ZGP crystal with excellent optical property. On the other hand, if the output power or tuning range of the mid-infrared femtosecond laser is output by singly using the OPO or DFG technology, the high-power continuous wide-tuning laser output near the mid-infrared wavelength is difficult to obtain directly, so that the difference frequency is considered through a plurality of nonlinear processes to improve the conversion efficiency, the generated femtosecond mid-infrared laser pulse has the advantages of wide tuning range and high repetition frequency, and the output mid-infrared femtosecond optical power can be improved by increasing the power of the initial pump light.
The significance of solving the problems and the defects is as follows: firstly, a1 mu m pump source laser is converted into two beams of femtosecond laser with longer wavelength by using OPO technology, the wavelength range of the femtosecond laser is tunable, and then the high-power mid-infrared tunable femtosecond laser is generated by using ZGP crystal with excellent optical property to carry out difference frequency. The scheme solves the problems of low output power and narrow tuning range of the existing femtosecond laser output technology, breaks through the design scheme of the traditional laser generation device, has clear system principle and relatively low requirements on a pumping source and a nonlinear crystal, generates the mid-infrared femtosecond laser with high output power, adjustable wavelength range and good stability of the output laser, can be widely applied to the aspects of free space optical communication, trace gas detection, environment monitoring, biomedicine and the like, and has great application value.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a high-power mid-infrared tunable femtosecond laser generation device, a control method and application.
The present invention is achieved as such, a high power mid-infrared tunable femtosecond laser generating apparatus, comprising:
the pumping module is used for pumping the optical parametric oscillation module;
the optical parametric oscillation module is used for converting input laser or pumping light into two output lights with lower frequencies;
and the difference frequency generation module is used for carrying out difference frequency on the two beams of laser generated by the optical parametric oscillation module to generate high-power mid-infrared tunable femtosecond laser.
Further, the pumping module includes: the high-power femtosecond oscillator, the first half-wave plate, the polarizing prism and the second half-wave plate;
the high-power femtosecond oscillator has the center wavelength of 1030nm, the pulse width of 100fs and the average power of more than 8W and is used for a pump optical parametric oscillation module; the first half-wave plate and the polarizing prism form a power attenuator which is used for changing the power of the pump light; the second half-wave plate is used for adjusting the polarization direction of the pump light and realizing the tunability of the power and the polarization of the pump light.
Further, the optical parametric oscillation module includes: the device comprises a first focusing lens, a first concave mirror, a nonlinear crystal and a second concave mirror;
the first focusing lens is used for focusing the laser output by the pumping source on the nonlinear crystal to enable the spot size of the incident light to be matched with the spot size of the oscillation light in the cavity; the nonlinear crystal is used for generating tunable signal light and pump light required by a subsequent difference frequency generation module; the first concave mirror is used for transmitting pump light and reflecting signal light at the same time, the second concave mirror is used for transmitting the pump light and idler frequency light and reflecting the signal light at the same time, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror.
Further, the nonlinear crystal is a KTA crystal, and is characterized in that a crystal cutting angle theta is 41.3 degrees,
the length is 2mm, and the range of the size of a light spot which is focused by the pump light and is incident on the crystal is 40-70 mu m; the KTA crystal is coated with antireflection films on two sides for pump light and signal light, the output of 1.5-1.9 mu m signal light is obtained through angle tuning, the output power is more than 2W, the corresponding output idler frequency light wavelength range is 2.3-3.2 mu m, and the output power is more than 1W.
Furthermore, the optical parametric oscillation module further comprises a first high-reflection mirror, a second high-reflection mirror, a third high-reflection mirror and an output mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are used for performing high reflection on the signal light and keeping the signal light to oscillate in the cavity; the output mirror is used for transmitting signal light, is placed on the one-dimensional translation table and is used for adjusting the length of the optical parametric oscillation cavity and achieving cavity length matching.
Further, the difference frequency generating module comprises: a third focusing lens, a nonlinear crystal, a fourth focusing lens;
the third focusing lens is used for focusing the pump light and the signal light which are collinear by the laser to the nonlinear crystal so that the size of an incident light spot of the third focusing lens is matched with that of a light spot in the cavity; the nonlinear crystal is used for performing difference frequency on the signal light and the idler frequency light generated by the optical parametric oscillation module as pump light and signal light respectively to obtain high-power mid-infrared tunable femtosecond laser; the fourth focusing lens is used for collimating and outputting the generated high-power intermediate infrared femtosecond laser, and the nonlinear crystal is arranged between the third focusing lens and the fourth focusing lens;
the nonlinear crystal is a ZGP crystal, and is characterized in that the cutting angle of the crystal is 74.3 degrees,
the crystal cutting angle theta is 55.8 degrees, and the output of the differential frequency light is 4-7 mu m,
the light source is used for outputting 7-9 mu m difference frequency light, and the required crystal length is 1 mm; by angle phase matching tuning, the adjustable mid-infrared femtosecond laser in the whole wavelength range of 4-9 μm is obtained, and the output power of the laser is more than 100mW in the whole idler frequency range.
Further, a second focusing lens and a time delay device are arranged between the idler frequency light output end of the optical parametric oscillation module and a third focusing lens of the difference frequency generation module, and are used for focusing and collimating the generated idler frequency light and enabling the idler frequency light to be overlapped and matched with the signal light in space and time.
Further, a first beam splitter is arranged in front of the difference frequency generation module and used for reflecting the idler frequency light output by the OPO module, transmitting the signal light and enabling the two beams of light to simultaneously enter a third focusing lens for focusing; and a second beam splitter is arranged behind the difference frequency generation module and is used for transmitting the high-power tunable intermediate infrared laser generated by the difference frequency and reflecting the rest light.
Another object of the present invention is to provide a control method of the high power mid-infrared tunable femtosecond laser generation device, the control method including:
firstly, a high-power femtosecond oscillator is operated and used as a pumping source for pumping an OPO optical parametric oscillation module and outputting pumping light; the first half-wave plate and the polarizing prism form a power attenuator, the power of the pump light can be changed by rotating the first half-wave plate, and the second half-wave plate is used for adjusting the polarization direction of the pump light so as to realize the tunability of the power and the polarization of the pump light;
the pumping light is transmitted by the high-reflection mirrors a1 and a2 and is focused on the nonlinear crystal KTA through the first focusing lens, and the optical parametric oscillation process is carried out in the OPO cavity to generate signal light and idler frequency light; the first concave mirror is highly transparent to the pump light and highly reflective to the signal light, the second concave mirror is highly transparent to the pump light and the idler frequency light and highly reflective to the signal light, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are also high-reflection for the signal light, and continuous tunable signal light and idler frequency light output is realized by changing the phase matching angle of the KTA crystal; the signal light is output through an output mirror, reflected twice by high-reflection mirrors c1 and c2 and then superposed with idler frequency light;
arranging a second focusing lens at the output position of the idler frequency light to enable the size of the idler frequency light spot to be matched with that of the signal light spot, and delaying the light by arranging high-reflection mirrors b1, b2 and b3 to enable the light to be combined with the signal light at the same time;
the first beam splitter is used for transmitting the signal light, reflecting the idler frequency light, and focusing the idler frequency light on the nonlinear crystal ZGP through the third focusing lens to perform a difference frequency generation process; tunable signal light and idler frequency light output by the OPO optical parametric oscillation module are used as pump light and signal light of a subsequent difference frequency generation module to generate a difference frequency effect, high-power tunable intermediate infrared femtosecond laser is output, and the high-power tunable intermediate infrared femtosecond laser is focused and collimated by a fourth focusing lens; the second beam splitter is used for transmitting the high-power tunable intermediate infrared laser and reflecting the rest light.
The invention also aims to provide an application of the high-power intermediate infrared tunable femtosecond laser generation device in free space optical communication, trace gas detection, environment monitoring or biomedicine.
By combining all the technical schemes, the invention has the advantages and positive effects that: the invention adopts a high-power 1-micron laser for pumping, utilizes the technology of combining Optical Parametric Oscillation (OPO) and Difference Frequency Generation (DFG), and adopts ZGP crystals for difference frequency generation, and finally outputs the mid-infrared femtosecond laser, which not only has the advantage of high power, but also has tunable wavelength and great application value. The high-power tunable intermediate infrared femtosecond laser can be obtained, and the high power, high repetition frequency and wide tuning of the output laser are ensured to a certain extent by utilizing the research scheme of OPO + DFG.
The high-power femtosecond oscillator pump OPO optical parametric oscillation module generates tunable signal light and idler frequency light which are respectively used as pump light and signal light required by the DFG difference frequency generation module to generate mid-infrared femtosecond laser, and the output laser has the characteristic of high-power tunable.
The invention adopts the OPO + DFG combination scheme to obtain the high-power mid-infrared tunable femtosecond laser, solves the problems of low output power and narrow tuning range of the existing femtosecond laser output technology, breaks through the design scheme of the traditional laser generating device, and obtains the mid-infrared femtosecond laser by using the combination technology.
The femtosecond laser generated by the invention has high output power and adjustable wavelength range, and meanwhile, the system has clear principle, flexible and simple structure and relatively low requirement on pumping sources and nonlinear crystals.
Drawings
FIG. 1 is a schematic structural diagram of a high-power mid-infrared tunable femtosecond laser generation device provided by an embodiment of the invention;
in fig. 1: 1. a high power femtosecond oscillator; 2. a first half wave plate; 3. a polarizing prism; 4. a second half-wave plate; 5. a first focusing lens; 6. a first concave mirror; 7. a nonlinear crystal KTA; 8. a second concave mirror; 9. a first high-reflection mirror; 10. a second high-reflection mirror; 11. a third high-reflection mirror; 12. an output mirror; 13. a second focusing lens; 14. a first beam splitter; 15. a third focusing lens; 16. a nonlinear crystal ZGP; 17. a fourth focusing lens; 18. and a second beam splitter. a1, a 2: a 45 DEG plane high reflection mirror (1030 nm); b1, b2, b 3: 45 DEG plane high reflection mirror (2300 and 3200 nm); c1, c 2: 45 DEG planar high-reflection mirror (1500-1900 nm).
Fig. 2 shows that under the KTA crystal class ii phase matching condition provided by the embodiment of the present invention, the pump light is 1030nm, the tunable range of the output signal light is 1.5 to 1.9 μm, the tunable range of the corresponding idler wavelength is 2.3 to 3.2 μm, and the corresponding phase matching angle is 41.3 to 46.4 degrees.
Fig. 3 shows that under the condition of ZGP crystal class i phase matching, tunable signal light and idler light generated by the optical parametric oscillation module are used as pump light and signal light respectively to perform a difference frequency process to generate idler light, and meanwhile, in consideration of a large transmittance, a range of the corresponding pump light is 1.65-1.85 μm, a range of the signal light is 2.32-2.74 μm, a range of the output idler light is 4-9 μm, and a corresponding phase matching angle is 53.7-86.2 degrees.
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 high-power intermediate infrared tunable femtosecond laser generation device, a control method and application thereof, and the invention is described in detail below with reference to the accompanying drawings.
The invention provides a scheme which has clear system principle, simple structure and relatively low requirement on a pumping source and a nonlinear crystal to obtain the mid-infrared femtosecond laser, namely a high-power mid-infrared tunable femtosecond laser generating device designed by utilizing the OPO + DFG combined technology.
As shown in fig. 1, the present invention is a high-power mid-infrared tunable femtosecond laser generating apparatus designed by using a combination technology of OPO + DFG, which includes three modules: a pumping module, an Optical Parametric Oscillation (OPO) module, and a Difference Frequency Generation (DFG) module.
The pumping module is used for pumping the OPO optical parametric oscillation module;
specifically, the pumping module includes: the high-power femtosecond oscillator comprises a high-power femtosecond oscillator 1, a first half-wave plate 2, a polarizing prism 3 and a second half-wave plate 4. The high-power femtosecond oscillator 1 is used for pumping an OPO optical parametric oscillation module; the first half wave plate 2 and the polarizing prism 3 form a power attenuator which is used for changing the power of the pump light; the second half-wave plate 4 is used for adjusting the polarization direction of the pump light, and finally the tunability of the power and the polarization of the pump light is realized.
The Optical Parametric Oscillation (OPO) module is configured to convert input laser light (pump light) into two output light beams (signal light and idler light) with lower frequencies;
specifically, the optical parametric oscillation module is used for generating tunable signal light (1.5-1.9 μm) and idler light (2.3-3.2 μm) to prepare for a subsequent difference frequency generation module. The first focusing lens 5 is used for focusing the pump light onto the nonlinear crystal KTA, so that the size of a light spot is consistent with that of an oscillation light spot in the cavity, the light transmission time is consistent with that of the oscillation light in the cavity, and synchronous pumping is kept. And further determining parameters and distances of each element in the resonant cavity by simulating an OPO cavity type, so that the signal light oscillates in the cavity, the optical parametric oscillation process is ensured, and the generated signal light and idler light are output at two ends.
The Difference Frequency Generation (DFG) module is used for carrying out difference frequency on the two beams of laser generated by the OPO module to generate high-power mid-infrared tunable femtosecond laser;
specifically, the difference frequency generation module is used for generating high-power tunable mid-infrared femtosecond laser (4-9 μm) by taking the tunable signal light and the idler frequency light output by the parametric oscillation module as pump light and signal light required by difference frequency. The third focusing lens 15 is used for focusing the pump light and the signal light which are collinear by the laser to the nonlinear crystal ZGP16, and under the condition that the laser peak power density is smaller than the crystal damage threshold, the laser focusing light spot is made as small as possible to obtain the output of the high-power difference frequency light. Meanwhile, the nonlinear crystal ZGP16 is used for generating a difference frequency effect so as to obtain the mid-infrared laser, and the fourth focusing lens 17 is used for collimating and outputting the generated high-power mid-infrared femtosecond laser.
Specifically, a second focusing lens 13 and a time delay device are disposed between the idler light output end of the Optical Parametric Oscillation (OPO) module and the third focusing lens 15 of the difference frequency generation module, and are used for focusing and collimating the generated idler light and enabling the idler light to coincide and match with the signal light in space and time.
Specifically, a first beam splitter 14 is disposed in front of the Difference Frequency Generation (DFG) module to reflect the idler frequency light output by the OPO module, transmit the signal light, and make two beams of light simultaneously incident on a third focusing lens 15 for focusing; and a second beam splitter 18 is arranged behind the difference frequency generation module and used for transmitting the high-power tunable intermediate infrared laser generated by the difference frequency and reflecting the rest light.
The invention firstly operates a high-power femtosecond oscillator 1 which is used as a pumping source for pumping an OPO optical parametric oscillation module and outputs pumping light with the central wavelength of 1030nm and the average power of more than 8W. The first half-wave plate 2 and the polarizing prism 3 form a power attenuator, the power of the pump light can be changed by rotating the first half-wave plate, and the second half-wave plate 4 is used for adjusting the polarization direction of the pump light, so that the tunability of the power and the polarization of the pump light is realized. The pumping light is transmitted by high reflection mirrors a1 and a2 and is focused on a nonlinear crystal (KTA)7 through a first focusing lens 5, and an optical parametric oscillation process is carried out in an OPO cavity to generate signal light and idler frequency light. The first concave mirror 6 is highly transparent to the pump light and highly reflective to the signal light, the second concave mirror 8 is highly transparent to the pump light and the idler frequency light and highly reflective to the signal light, and the nonlinear crystal 7 is arranged between the first concave mirror and the second concave mirror. The first high reflection mirror 9, the second high reflection mirror 10, and the third high reflection mirror 11 are also high-reflective to the signal light, keeping it oscillating in the cavity. By changing the phase matching angle of the KTA crystal, continuously tunable signal light and idler frequency light output can be realized. The signal light is output through the output mirror 12, reflected twice by the high reflection mirrors c1 and c2, and then superposed with the idler frequency light. The second focusing lens 13 is disposed at the idler light output position to match the idler light spot size with the signal light spot size, and the light is delayed and combined with the signal light at the same time by disposing the high-reflection mirrors b1, b2, b 3. The beam splitter 14 is used to transmit the signal light, reflect the idler light, and it is focused on a nonlinear crystal (ZGP)16 via a third focusing lens 15 to perform a difference frequency generation process. Namely, the tunable signal light and the idler frequency light output by the OPO optical parametric oscillation module are used as the pump light and the signal light of the subsequent difference frequency generation module to generate the difference frequency effect, the tunable intermediate infrared femtosecond laser with high power is output, and the tunable intermediate infrared femtosecond laser is focused and collimated by the fourth focusing lens 17 to be output. The beam splitter 18 is used for transmitting the high-power tunable mid-infrared laser and reflecting the rest light.
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 high-power intermediate infrared tunable femtosecond laser generation device is characterized by comprising:
the pumping module is used for pumping the optical parametric oscillation module;
the optical parametric oscillation module is used for converting input laser or pumping light into two output lights with lower frequencies;
and the difference frequency generation module is used for carrying out difference frequency on the two beams of laser generated by the optical parametric oscillation module to generate high-power mid-infrared tunable femtosecond laser.
2. The high power mid-infrared tunable femtosecond laser generation apparatus of claim 1, wherein the pumping module includes: the high-power femtosecond oscillator, the first half-wave plate, the polarizing prism and the second half-wave plate;
the high-power femtosecond oscillator has the center wavelength of 1030nm, the pulse width of 100fs and the average power of more than 8W and is used for a pump optical parametric oscillation module; the first half-wave plate and the polarizing prism form a power attenuator which is used for changing the power of the pump light; the second half-wave plate is used for adjusting the polarization direction of the pump light and realizing the tunability of the power and the polarization of the pump light.
3. The high power mid-infrared tunable femtosecond laser generation apparatus according to claim 1, wherein the optical parametric oscillation module includes: the device comprises a first focusing lens, a first concave mirror, a nonlinear crystal and a second concave mirror;
the first focusing lens is used for focusing the laser output by the pumping source on the nonlinear crystal to enable the spot size of the incident light to be matched with the spot size of the oscillation light in the cavity; the nonlinear crystal is used for generating tunable signal light and pump light required by a subsequent difference frequency generation module; the first concave mirror is used for transmitting pump light and reflecting signal light at the same time, the second concave mirror is used for transmitting the pump light and idler frequency light and reflecting the signal light at the same time, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror.
4. The high power mid-infrared tunable femtosecond laser generation apparatus according to claim 3, wherein the nonlinear crystal is a KTA crystal, characterized in that a crystal cutting angle θ is 41.3 °,
length of 2mm, pump light concentrationThe size range of the light spot of the focal incident on the crystal is 40-70 μm; the KTA crystal is coated with antireflection films on two sides for pump light and signal light, the output of 1.5-1.9 mu m signal light is obtained through angle tuning, the output power is more than 2W, the corresponding output idler frequency light wavelength range is 2.3-3.2 mu m, and the output power is more than 1W.
5. The high power mid-infrared tunable femtosecond laser generation apparatus according to claim 1, wherein the optical parametric oscillation module further comprises a first high reflection mirror, a second high reflection mirror, a third high reflection mirror, an output mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are used for performing high reflection on the signal light and keeping the signal light to oscillate in the cavity; the output mirror is used for transmitting signal light, is placed on the one-dimensional translation table and is used for adjusting the length of the optical parametric oscillation cavity and achieving cavity length matching.
6. The high power mid-infrared tunable femtosecond laser generation apparatus according to claim 1, wherein the difference frequency generation module includes: a third focusing lens, a nonlinear crystal, a fourth focusing lens;
the third focusing lens is used for focusing the pump light and the signal light which are collinear by the laser to the nonlinear crystal so that the size of an incident light spot of the third focusing lens is matched with that of a light spot in the cavity; the nonlinear crystal is used for performing difference frequency on the signal light and the idler frequency light generated by the optical parametric oscillation module as pump light and signal light respectively to obtain high-power mid-infrared tunable femtosecond laser; the fourth focusing lens is used for collimating and outputting the generated high-power intermediate infrared femtosecond laser, and the nonlinear crystal is arranged between the third focusing lens and the fourth focusing lens;
the nonlinear crystal is a ZGP crystal, and is characterized in that the cutting angle of the crystal is 74.3 degrees,
the crystal cutting angle theta is 55.8 degrees, and the output of the differential frequency light is 4-7 mu m,
the light source is used for outputting 7-9 mu m difference frequency light, and the required crystal length is 1 mm; by angle phase matching tuning, the adjustable mid-infrared femtosecond laser in the whole wavelength range of 4-9 μm is obtained, and the output power of the laser is more than 100mW in the whole idler frequency range.
7. The high power mid-infrared tunable femtosecond laser generation apparatus as set forth in claim 1, wherein a second focusing lens and a time delay means are disposed between the idler light output end of the optical parametric oscillation module and the third focusing lens of the difference frequency generation module, for focusing and collimating the generated idler light and making it coincide with the signal light in space and time.
8. The high-power mid-infrared tunable femtosecond laser generation device according to claim 1, wherein a first beam splitter is arranged in front of the difference frequency generation module to reflect the idler frequency light output by the OPO module, transmit the signal light, and make two beams of light simultaneously incident on a third focusing lens for focusing; and a second beam splitter is arranged behind the difference frequency generation module and is used for transmitting the high-power tunable intermediate infrared laser generated by the difference frequency and reflecting the rest light.
9. A control method of the high-power middle infrared tunable femtosecond laser generation device according to any one of claims 1 to 8, characterized in that the control method comprises the following steps:
firstly, a high-power femtosecond oscillator is operated and used as a pumping source for pumping an OPO optical parametric oscillation module and outputting pumping light; the first half-wave plate and the polarizing prism form a power attenuator, the power of the pump light can be changed by rotating the first half-wave plate, and the second half-wave plate is used for adjusting the polarization direction of the pump light so as to realize the tunability of the power and the polarization of the pump light;
the pumping light is transmitted by the high-reflection mirrors a1 and a2 and is focused on the nonlinear crystal KTA through the first focusing lens, and the optical parametric oscillation process is carried out in the OPO cavity to generate signal light and idler frequency light; the first concave mirror is highly transparent to the pump light and highly reflective to the signal light, the second concave mirror is highly transparent to the pump light and the idler frequency light and highly reflective to the signal light, and the nonlinear crystal is arranged between the first concave mirror and the second concave mirror;
the first high-reflection mirror, the second high-reflection mirror and the third high-reflection mirror are also high-reflection for the signal light, and continuous tunable signal light and idler frequency light output is realized by changing the phase matching angle of the KTA crystal; the signal light is output through an output mirror, reflected twice by high-reflection mirrors c1 and c2 and then superposed with idler frequency light;
arranging a second focusing lens at the output position of the idler frequency light to enable the size of the idler frequency light spot to be matched with that of the signal light spot, and delaying the light by arranging high-reflection mirrors b1, b2 and b3 to enable the light to be combined with the signal light at the same time;
the first beam splitter is used for transmitting the signal light, reflecting the idler frequency light, and focusing the idler frequency light on the nonlinear crystal ZGP through the third focusing lens to perform a difference frequency generation process; tunable signal light and idler frequency light output by the OPO optical parametric oscillation module are used as pump light and signal light of a subsequent difference frequency generation module to generate a difference frequency effect, high-power tunable intermediate infrared femtosecond laser is output, and the high-power tunable intermediate infrared femtosecond laser is focused and collimated by a fourth focusing lens; the second beam splitter is used for transmitting the high-power tunable intermediate infrared laser and reflecting the rest light.
10. Use of the high power mid-infrared tunable femtosecond laser generation device according to any one of claims 1 to 8 in free space optical communication, trace gas detection, environmental monitoring or biomedicine.
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