Single-frequency dual-wavelength dual-pulse optical parametric oscillation laserTechnical Field
The invention relates to a pulse optical parametric oscillation laser, in particular to a single-frequency dual-wavelength dual-pulse optical parametric oscillation laser.
Technical Field
The airborne and spaceborne integral path differential absorption radar system is an effective remote sensing device for measuring the polluted gas such as water vapor, carbon dioxide, methane and the like in the atmosphere, and is a current earth carbon circulation research hotspot. The most important of radars is a single frequency pulsed laser source, which requires both high pulse energy and high frequency stability, while requiring multiple wavelength outputs. Therefore, the multi-wavelength single-frequency pulse laser with reliable performance has practical significance.
The current laser for the laser differential absorption radar is a research hot spot, and the seed injection single-frequency single-pulse optical parametric oscillator can encounter the following problems in the implementation process.
Firstly, seed laser is injected into a resonant cavity, a four-cavity mirror is finely tuned to enable the seed to be transmitted in the resonant cavity for multiple times, and the fine degree of a laser interference signal transmitted by the seed through the resonant cavity is used for representing that the resonant cavity is completely tuned; then, a nonlinear crystal is placed, and angle adjustment is performed to meet the requirement of pulse output spectrum center wavelength. Due to individual variability of the embedded crystals, the transmission interference signal of the seed laser may be changed, and the cavity mirror cannot be adjusted any more.
Secondly, in order to realize high output frequency stability of the parametric optical pulse, namely, jitter of a laser pulse frequency value to 1MHz magnitude, a frequency control component is required to generate a small step length to adjust the cavity length, a high-precision control component is required, and ripple waves of a PZT driving circuit are controlled, so that challenges are brought to long-term reliable operation of electronics.
Thirdly, the previous method can only realize the output of single-wavelength optical parametric oscillation laser, and the output pulse frequency needs to be controlled by adopting a novel method for how to select the second seed laser frequency of the single-frequency double-wavelength double-pulse optical parametric oscillator.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a single-frequency dual-wavelength dual-pulse optical parametric oscillation laser which is simple in optical calibration, ensures high reliability while reducing the precision requirement on a frequency stabilizing component, and simultaneously provides a second seed laser frequency selection basis and a second pulse laser frequency stabilizing method.
The technical scheme of the invention is as follows:
the single-frequency dual-wavelength dual-pulse optical parametric oscillation laser is characterized by comprising a single-frequency seed laser, a high-stability optical parametric oscillator resonant cavity, a frequency control assembly and a single-frequency dual-pulse train pumping source:
the single frequency seed laser comprises: the device comprises a first seed laser, a second seed laser, a magneto-optical switch, a polarization maintaining fiber beam splitter, a collimating mirror, an isolator, a focusing mirror, a first half-wave plate and a bicolor mirror, wherein the output end of the first seed laser is connected with the input end of the polarization maintaining fiber beam splitter, the polarization maintaining fiber beam splitter splits laser output by the first seed laser, the first output end of the polarization maintaining fiber beam splitter is connected with the first input end of the magneto-optical switch, the output end of the second seed laser is connected with the second input end of the magneto-optical switch, and the seed laser output by the output end of the magneto-optical switch sequentially passes through the collimating mirror, the isolator, the focusing mirror, the first half-wave plate and the bicolor mirror and then enters the resonant cavity of the high-stability optical parametric oscillator;
the high-stability optical parametric oscillator resonant cavity comprises a high-stability resonant cavity shell, a first cavity mirror, a second cavity mirror, a third cavity mirror, a fourth cavity mirror, a compensation plate, a nonlinear crystal, a thermoelectric cooling plate, a piezoelectric ceramic plate, a first photoelectric detector and an extra-cavity 45 DEG reflecting mirror, wherein the four cavity mirrors are arranged in the high-stability resonant cavity shell, the first cavity mirror, the second cavity mirror, the third cavity mirror and the fourth cavity mirror are sequentially arranged along the transmission direction of seed laser transmitted by the bicolor mirror, and finally the seed laser is output through the first cavity mirror and the extra-cavity 45 DEG reflecting mirror, the nonlinear crystal is arranged on a light path between the first cavity mirror and the second cavity mirror and is arranged in the thermoelectric cooling plate, the third cavity mirror is fastened on the piezoelectric ceramic plate, the compensation plate is arranged between the third cavity mirror and the fourth cavity mirror, and the first photoelectric detector is arranged on an optical path extension line of the fourth cavity mirror;
the frequency control assembly consists of a second half wave plate, a coupling mirror, an acousto-optic modulator, a polarization maintaining fiber coupler, a second photoelectric detector, a data acquisition processing unit, a digital-to-analog conversion assembly and a piezoelectric ceramic driving circuit in sequence; the second half-wave plate is positioned in the transmission direction of the 45-degree reflecting mirror outside the cavity, and the second input end of the polarization maintaining fiber coupler is connected with the second output end of the fiber beam splitter; the output end of the polarization maintaining fiber coupler is connected with the input end of the second photoelectric detector, and the output end of the second photoelectric detector is connected with the first input end of the data acquisition processing unit; the output end of the data acquisition processing unit is connected with the piezoelectric ceramic driving circuit through the digital-to-analog conversion component, and the output end of the piezoelectric ceramic driving circuit is connected with the piezoelectric ceramic sheet;
the single-frequency double-pulse-train pumping source comprises a single-frequency pulse-train laser and an electronic controller, a third half-wave plate and a beam shrinking lens group thereof, wherein the single-frequency pulse-train laser outputs double-pulse-train pumping laser with fixed repetition frequency, the double-pulse-train pumping laser sequentially passes through the third half-wave plate and the beam shrinking lens group and is reflected by the bicolor mirror to enter the high-stability optical parametric oscillator resonant cavity, the output end of the electronic controller is connected with the control end of the magneto-optical switch, a time sequence control signal is provided for the magneto-optical switch, so that the switching time of the wavelengths of the first seed laser and the second seed laser is determined, and the output end of the electronic controller is also connected with the second input end of the data acquisition processing unit and provides a trigger signal for the data acquisition processing unit;
under the control of the frequency control component, after the magneto-optical light-on receives a trigger signal, laser output by the first wavelength seed laser is injected into the resonant cavity of the high-stability optical parametric oscillator through the magneto-optical light-on, an initial voltage is applied to the piezoelectric ceramic plate, when pump laser of a single-frequency double-pulse string output by the single-frequency pulse string laser is input into the resonant cavity of the high-stability optical parametric oscillator through the double-color mirror, the resonant cavity of the high-stability optical parametric oscillator obtains parametric oscillation pulse string laser, free space laser is output by the coupling mirror through the second half-wave plate and the coupling mirror, the free space laser is coupled into the polarization maintaining optical fiber, and then the first pulse in the parametric light pulse string and the other part of the first wavelength seed laser output by the optical fiber beam splitter are subjected to frequency beat signal 1 through the polarization maintaining optical fiber coupler; when the magneto-optical light is received by a trigger signal provided by single-frequency double-pulse serial laser electronics between a first pulse and a second pulse of the parametric light pulse string, the laser of the magneto-optical light is switched into a second wavelength seed laser and injected into a resonant cavity of the high-stability optical parametric oscillator to obtain the second pulse in the parametric light pulse string; the beat frequency signal 1 is obtained by the data acquisition and processing unit, the beat frequency signal frequency value obtained by the data acquisition and processing unit is compared with the reference modulation frequency, the difference value is subjected to digital-to-analog conversion assembly to obtain the corresponding resonant cavity length tuning quantity, the piezoelectric ceramic driving circuit applies corresponding voltage to the piezoelectric ceramic chip to tune the resonant cavity length, and finally, the first pulse frequency of the optical parametric oscillator is locked on the frequency of the first seed laser; after the first pulse emits light, the voltage of the piezoelectric ceramic driving circuit is kept unchanged until the second pulse arrives, and the wavelength of the second pulse is controlled by the frequency of the second seed laser.
The covered wavelength bands of the first seed laser and the second seed laser include, but are not limited to, 2 μm, 1.57 μm, 1.64 μm, 0.97 μm and 0.94 μm, and the wavelength difference between the second seed laser and the first seed laser is an integer multiple of the free spectral range of the optical parametric oscillator cavity.
The pumping pulse train output by the single-frequency pulse train laser is a single-wavelength double-pulse train, and the intervals among pulses in the pulse train are regulated in a certain range by the electronic controller according to the requirement; the parametric light pulse train formed by the seed lasers is a pulse train with double wavelengths, the wavelengths of the parametric light pulse train are respectively consistent with those of the first seed lasers and the second seed lasers, and the pulse intervals are consistent with the intervals of the pumping pulse trains.
The high-stability optical parametric oscillator resonant cavity shell is formed by processing an integrated structure, the first cavity mirror and the second cavity mirror are directly fixed on the vertical wall of the shell, the third cavity mirror and the fourth cavity mirror are fixed on the vertical wall of the high-stability resonant cavity shell through the adapter, the nonlinear crystal is arranged in the heat sink metal block, the temperature is tunable, the metal block is fixed on the bottom plate of the resonant cavity shell, and the compensation mirror is fixed on the bottom plate of the resonant cavity shell through the adapter.
The working principle of the invention is as follows:
a single-frequency dual-wavelength dual-pulse optical parametric oscillation laser with high frequency stability is a single-frequency dual-wavelength dual-pulse optical parametric oscillation laser which is realized by a single-frequency dual-pulse train pumping source, dual-wavelength seed switching injection and respectively controlling output pulse frequencies by combining a heterodyne beat frequency method frequency stabilization technology. According to the principle of the transmission intensity of laser frequency through the resonant cavity, the wavelength difference of the two selected injected seeds is required to be an integral multiple of a free spectrum range corresponding to the resonant cavity. Once the first seed laser frequency is determined, the second seed laser frequency will be related to the cavity length and its finesse. Based on the high stability of the integrated resonant cavity, only the first wavelength pulse needs to be subjected to frequency locking control; after the first pulse is output, the voltage of the piezoelectric ceramic driving circuit is kept unchanged after the first wavelength pulse until the second wavelength pulse passes through a period, so that the resonant cavity length of the optical parametric oscillator is kept unchanged, and a control signal enables the magneto-optical switch to enable the second wavelength seed laser to enter the resonant cavity and lock and control the frequency of the second pulse.
Compared with the prior art, the invention has the following advantages:
1. the single-frequency dual-wavelength dual-pulse laser is obtained by utilizing dual-wavelength seed injection, and the dual wavelengths can be adjusted in a large range according to the needs.
2. And the compensating sheet is arranged in the cavity, so that the optical assembly process of the resonant cavity is improved.
3. The relation between the wavelength difference of the seed source required by the multi-wavelength pulse and the length of the resonant cavity of the optical parametric oscillator is given, stable multi-wavelength multi-pulse output is ensured to be obtained, and meanwhile, the second pulse frequency control method is provided based on the high stability of the resonant cavity of the integrated optical parametric oscillator.
4. Experiments show that the laser radar device has the characteristics of narrow linewidth, high frequency stability, double-wavelength double-pulse single-frequency output, wavelength expansion, strong anti-interference capability, stability and reliability, can further amplify optical parameters to improve pulse energy, can be used for an atmospheric component detection laser radar laser light source, and can meet the application requirements of complex environments such as airborne and spaceborne.
Drawings
FIG. 1 is a block diagram of a high frequency stability single frequency dual wavelength dual pulse optical parametric oscillation laser of the present invention;
FIG. 2 is a schematic diagram of the pulse timing and wavelength of pump laser and parametric laser in the multi-wavelength narrow linewidth pulse laser of the present invention.
Detailed Description
The invention is further illustrated in the following examples and figures, which should not be taken to limit the scope of the invention.
As shown in fig. 1, fig. 1 is a structural block diagram of a high-frequency stability dual-wavelength dual-pulse optical parametric oscillation laser of the present invention, and as can be seen from the figure, the dual-wavelength dual-pulse optical parametric oscillation laser of the present invention includes four parts of a single-frequency seed laser 1, a resonant cavity 2 of the high-stability optical parametric oscillator, a frequency control component 3 and a single-frequency dual-pulse train pumping source 4:
the single frequency seed laser 1 comprises: the laser beam splitter comprises a first seed laser 101, a second seed laser 102, a magneto-optical switch 103, a polarization maintaining fiber beam splitter 104, a collimating mirror 105, an isolator 106, a focusing mirror 107, a first half-wave plate 108 and a dichroic mirror 109, wherein the output end of the first seed laser 101 is connected with the input end of the polarization maintaining fiber beam splitter 104, the polarization maintaining fiber beam splitter 104 splits the laser output by the first seed laser 101, the first output end of the polarization maintaining fiber beam splitter 104 is connected with the first input end of the magneto-optical switch 103, the output end of the second seed laser 102 is connected with the second input end of the magneto-optical switch 103, and the seed laser output by the output end of the magneto-optical switch 103 sequentially passes through the collimating mirror 105, the isolator 106, the focusing mirror 107, the first half-wave plate 108 and the dichroic mirror 109 and then enters the resonant cavity 2 of the high-stability optical parametric oscillator;
the resonant cavity 2 of the high-stability optical parametric oscillator includes a high-stability resonant cavity housing 200, a first cavity mirror 201, a second cavity mirror 202, a third cavity mirror 203, a fourth cavity mirror 204, a compensation plate 205), a nonlinear crystal 206, a thermoelectric cooling plate 207, a piezoelectric ceramic plate 2010, a first photoelectric detector 2011 and an extra-cavity 45 ° mirror 2012, four cavity mirrors are disposed in the high-stability resonant cavity housing 200, the transmission directions of seed laser transmitted by the dual-color mirror 109 are sequentially the first cavity mirror 201, the second cavity mirror 202, the third cavity mirror 203 and the fourth cavity mirror 204, and finally the first cavity mirror 201 and the extra-cavity 45 ° mirror 2012 output the same, the nonlinear crystal 206 and the thermoelectric cooling plate 207 thereof are disposed on an optical path between the first cavity mirror 201 and the second cavity mirror 202, the third cavity mirror 203 is fastened on the piezoelectric ceramic plate 2010, the compensation plate 205 is disposed between the third cavity mirror 203 and the fourth cavity mirror 204, and the optical path of the fourth cavity mirror 204 is extended by the fourth cavity mirror 2011;
the frequency control assembly 3 is composed of a second half wave plate 301, a coupling mirror 302, a polarization maintaining fiber coupling acousto-optic modulator 303, a polarization maintaining fiber coupler 304, a second photoelectric detector 305, a data acquisition processing unit 306, a digital-to-analog conversion assembly 307 and a piezoelectric ceramic driving circuit 308 in sequence; the second half-wave plate 301 is located in the transmission direction of the 45 ° reflecting mirror 2012 outside the cavity, and the second input end of the polarization maintaining fiber coupler 304 is connected to the second output end of the fiber optic splitter 104; the output end of the polarization maintaining fiber coupler 304 is connected with the input end of the second photoelectric detector 305, and the output end of the second photoelectric detector 305 is connected with the first input end of the data acquisition and processing unit 306; the output end of the data acquisition processing unit 306 is connected with the piezoelectric ceramic driving circuit 308 through the digital-to-analog conversion component 307, and the output end of the piezoelectric ceramic driving circuit 308 is connected with the piezoelectric ceramic chip 2010;
the single-frequency double-pulse-train pumping source 4 comprises a single-frequency pulse-train laser and a power supply electronic controller 401, a third half-wave plate 402 and a beam shrinking lens group 403 thereof, wherein the single-frequency pulse-train laser outputs double-pulse-train pumping laser with fixed repetition frequency, after passing through the third half-wave plate 402 and the beam shrinking lens group 403 in sequence, the pumping laser is reflected by the double-color mirror 109 and enters the high-stability optical parametric oscillator resonant cavity 2, the output end of the power supply electronic controller is connected with the control end of the magneto-optical switch 103 to provide a time sequence control signal for the magneto-optical switch 103, the switching moment of the first seed laser 101 and the second seed laser 102 is defined, and the output end of the power supply electronic controller is also connected with the second input end of the data acquisition processing unit 306 to provide a trigger signal for the data acquisition processing unit 306;
under the control of the frequency control component 3, after the magneto-optical light-opening 103 receives the trigger signal, the laser light output by the first wavelength seed laser 101 is injected into the resonant cavity 2 of the high-stability optical parametric oscillator through the magneto-optical light-opening 103, an initial voltage is applied to the piezoelectric ceramic wafer 2010, when the pumping laser light of the single-frequency double-pulse string output by the single-frequency pulse string laser is input into the resonant cavity 2 of the high-stability optical parametric oscillator through the dichroic mirror 109, the resonant cavity 2 of the high-stability optical parametric oscillator obtains parametric oscillation pulse string laser light, the free space laser light is output by the coupling mirror 302 through the second half-wave plate 301, the free space laser light is coupled into the polarization maintaining optical fiber, and then the free space laser light is input into the polarization maintaining optical fiber coupler 304 through the acousto-optic modulator 303, and the other part of the first pulse of the parametric optical pulse string and the first wavelength seed laser light 101 output by the beam splitter 104 are beaten into beat frequency signals 1; between the first pulse and the second pulse of the parametric optical pulse train, when the magneto-optical light 103 receives the trigger signal provided by the single-frequency double-pulse serial laser electronic controller, the laser of the magneto-optical light 103 is switched to the second wavelength seed laser 102 and injected into the resonant cavity 2 of the high-stability optical parametric oscillator, so as to obtain the second pulse in the parametric optical pulse train;
the beat frequency signal 1 is obtained by the data acquisition and processing unit 306, the beat frequency signal frequency value obtained by processing is compared with the reference modulation frequency, the difference value is subjected to digital-to-analog conversion assembly 307 to obtain the corresponding resonant cavity length tuning quantity, the piezoelectric ceramic driving circuit 308 applies corresponding voltage to the piezoelectric ceramic piece 2010 to tune the resonant cavity length, and finally the first pulse frequency meeting the requirement of the optical parametric oscillator is locked on the frequency of the first seed laser 101; after the first pulse is emitted, the piezoceramic drive circuit 308 voltage remains unchanged until a second pulse arrives, the second pulse wavelength being controlled by the frequency of the second seed laser 102.
Examples
The single-frequency seed laser 1 comprises a first seed laser 101 and a second seed laser 102, the laser wavelengths of the two single-frequency seeds are 1572.024nm and 1572.085nm respectively, the resonant cavity 2 is made of invar material, the nonlinear crystal 206 is a critical cut KTA crystal, and the compensation sheet 205 is fused silica glass. The optical fibers in the frequency control assembly 3 are all polarization maintaining 1550nm optical fibers, the frequency of the acousto-optic modulator 303 is shifted by 400MHz, the bandwidth of the second photoelectric detector 305 is 5GHz, and the bandwidth of the data acquisition card is 1GHz.
YAG double pulse train pumping source with single frequency Nd, as shown in figure 2, with repetition frequency 100Hz, double pulse interval 200 mu s, single pulse energy 9mJ. Meanwhile, FIG. 2 shows a schematic diagram of dual-wavelength dual-pulse output, wherein the pulse energy of the dual wavelength is-2 mJ, the first pulse wavelength is 1572.024nm, the frequency stability is RMS-0.3 MHz, the second pulse wavelength is 1572.085nm, the frequency stability is RMS-0.3 MHz, the interval between the two pulse wavelengths is-200 mu s, and the pulse energy can be regulated in a certain range by a pumping source.
Experiments show that the laser radar device has the characteristics of narrow linewidth, high frequency stability, double-wavelength double-pulse single-frequency output, wavelength expansion, strong anti-interference capability, stability and reliability, can further amplify optical parameters to improve pulse energy, can be used for an atmospheric component detection laser radar laser light source, and can meet the application requirements of complex environments such as airborne and spaceborne.