CN104184029A - Frequency locking method used for tunable laser in pulse type laser system - Google Patents
Frequency locking method used for tunable laser in pulse type laser system Download PDFInfo
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- CN104184029A CN104184029A CN201410403052.3A CN201410403052A CN104184029A CN 104184029 A CN104184029 A CN 104184029A CN 201410403052 A CN201410403052 A CN 201410403052A CN 104184029 A CN104184029 A CN 104184029A
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Abstract
The invention discloses a frequency locking method used for a tunable laser in a pulse type laser system. In the pulse interval time of the pulse type laser system, modulation is conducted on the frequency of laser output by the tunable seed laser through a servo control system and the light intensity can change along with the frequency after the laser passes through a frequency reference device; a photoelectric detector and a digital acquisition card are used for feeding back light intensity information to the servo control system, the servo control system output signals according to feedback data so as to enable the seed laser to be kept at the set locking frequency until a next pulse ends and the scanning process and the locking process are repeated. Thus, it can be guaranteed that the frequency of the laser output by the seed laser is kept on a locking point before every pulse light comes. The frequency locking method is simple and easy to implement and enables the locking frequency of the tunable seed laser to be locked on any frequency point within the reference range of the frequency reference device, the frequency is kept stable at the cavity die locking stage of a pulse system and no modulation is needed.
Description
Technical field
The present invention relates to laser frequency lock technical field, specifically a kind of frequency locking method for pulse type laser system tunable laser.
Background technology
Along with the development of laser technology, its application is more and more wider.In some application scenario, for example pulsed DIAL and molecular reaction dynamics research, the live width of paired pulses laser frequency and stability requirement are very high, and the optical parametric oscillator (Optical Parametric Oscillator) that yag crystal (Nd:YAG) pulse laser that mostly adopts seed to inject at present injects in conjunction with seed is realized.By chamber mode locking technology, can make the pulsed light frequency of output and seed injection continuous light be consistent, therefore the stability of pulsed light frequency is directly determined by the stability of seed light frequency.
Conventional tunable laser frequency locking method has lateral edges lock-in techniques and PDH lock-in techniques at present.The former general principle is that detection laser sees through the light intensity after frequency reference device (etalon, gas absorption cell etc.), keyed end is arranged on to the halfwidth degree place of transmitted spectrum one side, once signal light frequency transmitting skew, the light intensity receiving also can change thereupon, regulates sharp light frequency to make it return to keyed end by closed loop feedback system.The latter's general principle is by the frequency of frequency modulation technology modulated laser outside chamber or in chamber, laser is received by photodetector after by F-P chamber, then by the signal detecting and modulation signal mixing to obtain error signal, thereby by laser lock-on on specific frequency.
But these methods all exist certain shortcoming, interference and lasting accuracy that the former is subject to external environment are not high.If the latter adopts outer cavity modulation, can make device complexity; If regulate in employing chamber, make Output of laser frequency always in modulation condition.And, also there is a common problem in both, for example, if laser is subject to certain interference and makes frequency occur significantly to change to such an extent as to exceeded after the frequency reference scope (the absworption peak width of the bandwidth of etalon and molecule) of frequency reference device, will cause losing lock phenomenon.
These methods are applicable to need the occasion of continuous frequency locking, and are not suitable for pulse type laser system.There is no at present and a kind ofly can avoid above-mentioned shortcoming, simple and be applicable to the frequency locking method of seed laser in pulse type laser system.
Summary of the invention
The present invention, for addressing the above problem, has proposed a kind of frequency locking method of the tunable laser that is applicable to pulse type laser system, and technical scheme is as follows:
This method can realize with the device shown in Fig. 1, comprising: tunable seed laser, frequency reference device (etalon, gas absorption cell etc.), photodetector, Data Acquisition Card, servo-control system.A continuous laser part for tunable seed laser output is injected in pulse type laser system, and another part is for Frequency Locking.Pulse type laser system, by chamber mode locking technology, can be exported pulse laser and the laser frequency of single longitudinal mode and inject the consistent of light with seed.The signal that tunable seed laser can provide according to servo-control system changes the frequency of Output of laser, the transmitance difference of frequency reference device to different frequency laser, the light signal seeing through is converted to the signal of telecommunication by photodetector, Data Acquisition Card will feed back to servo-control system after the signal of telecommunication digitlization of photodetector output, and servo-control system makes its frequency stabilization on keyed end according to the tunable seed laser of this feedback signal control.
The concrete control flow of the method is as follows:
Fig. 2 is this device work wave sequential chart.T
0moment pulse laser transmitting finishes; T
1moment servo-control system starts output scanning signal, now tunable laser Output of laser frequency can change and change along with sweep signal, for convenience's sake, the laser frequency shown in figure is linear trend and changes, and in fact the method is equally applicable to the occasion of nonlinear change.Due to the transmitance difference of frequency reference device to different frequency laser, therefore the signal of photodetector output also can change, and shown in figure is by the situation after gas absorption cell; T
2the laser frequency ν that moment is corresponding
1the Frequency point that needs locking, the transmitance at this frequency place and frequency reference device centre frequency ν
0the ratio of the transmitance at place is a constant C, records T
3moment centre frequency ν
0the amplitude of place's photodetector output signal is V
0, this centre frequency is an absolute stable value, and is not that maximum (etalon) is exactly minimum (gas cell) in the transmitance at this frequency place, so this point can find easily.Then find signal amplitude V
1=C*V
0the sweep signal value of corresponding servo system output, obviously can find two values, but both has sequencing in time, selects that value needing to be designated as D
1.T
4the moment positive direction end of scan, starts along scanning in the other direction, at T
5moment reaches the output valve D that keyed end is corresponding
1, remain on ever since this value until scanning next time starts.T
5to T
6shorter during this period of time, can think frequency kept stable within this period of seed laser Output of laser, pulse type laser system during this period of time completes chamber mode locking, and the single longitudinal mode pulsed light frequency that makes output is also ν
1.During each pulse spacing, repeat scanner uni lock program, can ensure that the output frequency of pulse laser is locked in ν for a long time
1.
The present invention scans the method for frequency locking by the pulse spacing, can be by the Frequency Locking of tunable seed laser the arbitrary frequency point in frequency reference device term of reference; Keep stable and without modulation in chamber mode locking stage frequency; There is within the specific limits saltus step even if the frequency of seed laser is subject to the interference of certain factor, as long as make the term of reference that scanning frequency can covering frequence parametric device, the phenomenon of losing lock can not occur; Whole frequency locking device is simple, can obtain very high frequency stability.
Brief description of the drawings
Fig. 1: apparatus structure schematic diagram of the present invention.
Fig. 2: the work wave sequential chart of device of the present invention.
Embodiment
As shown in Figure 1, wherein pulse type laser system is the optical parametric oscillator that seed injects, and the pulsed light of 532nm can be converted to the pulsed light of 935nm, utilizes interferometric method to complete chamber mode locking, and pulse repetition is 10Hz; Tunable seed laser is semiconductor laser, can change by current-modulation the frequency of Output of laser, its outside control circuit can be converted into current modulated by voltage modulation signal, the corresponding relation of voltage and optical maser wavelength is approximately 10pm/V, output wavelength is adjusted on the absworption peak 935.6849nm of steam, and by the fiber optic splitter of 95:5, Output of laser is divided into 2 bundles, 95% energy injection is to optical parametric oscillator as seed light, and remaining 5% energy is for Frequency Locking; Frequency reference device is optical fiber low pressure steam gas cell, and the inside has been full of pure water vapour, and air pressure is 2500Pa, and absorption length is 1.6m; What photodetector adopted is photodiode, and by trans-impedance amplifier, current signal is enlarged into voltage signal; The sample rate of Data Acquisition Card and resolution are respectively 100M and 14bit, and voltage acquisition scope is 0～2.4V; Servo-control system is made up of field programmable gate array (FPGA) and digital to analog converter (DAC), and the resolution of DAC is 12bit, and output voltage range is 0～2.4V, and output voltage is directly used in the frequency of semiconductor laser modulation.
As shown in Figure 2, T
0moment impulse ejection finishes, and postpones after 2ms at T
1moment FPGA controls DAC and starts the stepping output scanning voltage with 0.01V, each output valve that changes, the frequency of semiconductor laser also can change thereupon, now also can change by the light intensity after gas cell, Data Acquisition Card is recorded photodetector amplitude output signal and is fed back to FPGA; Whole scanning process is 15ms, at T
4moment finishes, and then FPGA, according to the table of comparisons of each DAC output valve and sampled value, finds V
1=1.2V
0locating corresponding DAC output valve is D
1; FPGA starts to control DAC output valve and reduces gradually subsequently, the T after 10ms
5moment reaches D
1; At T
5to T
6in this 73ms, DAC output remains D
1, seed laser within this period frequency stabilization at ν
1, optical parametric oscillator completes chamber mode locking during this period, and final output frequency is ν
1pulsed light.Operation more than repeating within the next pulse spacing, ensures that the frequency of seed laser is locked in ν for a long time in the chamber mode locking stage like this
1.
Above-described specific embodiment; object, technical scheme and beneficial effect to invention further describe; what should emphasize is; the foregoing is only specific embodiments of the invention; be not limited to the present invention; every in the spirit and principles in the present invention, any amendment of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (1)
1. for a frequency locking method for pulse type laser system tunable laser, it is characterized in that method is as follows:
The invention discloses a kind of frequency locking method for pulse type laser system tunable laser, within the interpulse period of pulse type laser system, by servo-control system, the frequency of tunable seed laser Output of laser is modulated, laser by frequency reference device after light intensity can change with frequency change; Utilize photodetector and Data Acquisition Card that intensity signal is fed back to servo-control system, according to these feedback data, servo-control system output signal makes locking frequency that seed laser remains on setting until next end-of-pulsing, then repeat above scanner uni locking process, can ensure that like this frequency of seed laser Output of laser remains on keyed end before each pulsed light arrives.The present invention is simple, can be by the Frequency Locking of tunable seed laser the arbitrary frequency point in frequency reference device term of reference, stable and without modulation in the chamber of pulse system mode locking stage holding frequency.
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Cited By (5)
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| CN104568386A (en) * | 2014-12-30 | 2015-04-29 | 北京航天易联科技发展有限公司 | Laser wavelength screening method and device thereof |
| CN110501728A (en) * | 2018-05-16 | 2019-11-26 | 清华大学 | The frequency discrimination method and frequency discrimination device of signal when locating base station is jumped |
| CN112038881A (en) * | 2020-09-02 | 2020-12-04 | 山西大学 | Pump optical cavity enhanced double-resonance optical parametric oscillator and efficient conversion method |
| CN114295224A (en) * | 2021-11-30 | 2022-04-08 | 天津津航技术物理研究所 | Infrared TDI detector line frequency adjusting system and method |
| CN118501093B (en) * | 2024-05-14 | 2024-11-12 | 朗思传感科技(深圳)有限公司 | Absorption spectrum gas analyzer based on etalon laser frequency locking |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN104568386A (en) * | 2014-12-30 | 2015-04-29 | 北京航天易联科技发展有限公司 | Laser wavelength screening method and device thereof |
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| CN110501728B (en) * | 2018-05-16 | 2022-03-29 | 清华大学 | Frequency discrimination method and device for time hopping signal of positioning base station |
| CN112038881A (en) * | 2020-09-02 | 2020-12-04 | 山西大学 | Pump optical cavity enhanced double-resonance optical parametric oscillator and efficient conversion method |
| CN114295224A (en) * | 2021-11-30 | 2022-04-08 | 天津津航技术物理研究所 | Infrared TDI detector line frequency adjusting system and method |
| CN118501093B (en) * | 2024-05-14 | 2024-11-12 | 朗思传感科技(深圳)有限公司 | Absorption spectrum gas analyzer based on etalon laser frequency locking |
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| CN104184029B (en) | 2017-02-01 |
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