A fixed frequency and variable frequency multi-pulse laser device

Abstract

The application discloses a kind of fixed frequency and variable frequency multi-pulse laser emitting device, including three polaroids, four dichroic mirrors, reflecting mirror and four groups of cavities, each group of cavities includes back mirror, electro-optic Q switch and crystal.The first cavity emits first time pulse laser, interval time dt1 after second cavity emits second time pulse laser, then after interval time dt2, third cavity emits third time pulse laser, and after interval time dt3, fourth cavity emits fourth time pulse laser, repeat this process to form multi-pulse laser, wherein interval time dt1 is equal to interval time dt3, interval time dt2 can be continuously adjustable, to form fixed frequency and variable frequency multi-pulse laser.The device of the application can realize multiple trigger laser distribution results with adjustable time interval in a single sampling period, and further realizes the measurement of high time resolution of flow field, improves test efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic technology, in particular to a fixed frequency and variable frequency multi-pulse laser emitting device. BACKGROUND

[0002] In the PIV measurement process, the tracer particles are uniformly distributed in the flow field to scatter the laser, and the velocity field is obtained by analyzing and calculating the front and back two images through camera image acquisition. At present, the PIV system commonly uses a double-pulse laser as a light source system. The double-pulse laser emits two light pulses to illuminate the flow field in a very short time, and the camera takes two photos by twice exposure. The main parameters include light pulse energy E, pulse width τ, and time delay dt, also known as pulse interval. The current mainstream PIV light source system is a double-YAG solid pulse laser, whose output wavelength is 532 nm, light pulse energy E is 10-1000 mJ, pulse width τ is 5-10 ns, time delay dt is 10-50 μs, and laser pulse frequency f is high energy and low frequency, usually less than 25 Hz, but low energy and high frequency can reach 10 kHz. Large field of view and high time resolution flow field measurement requires a set of high frequency-high energy PIV equipment, but the two indicators of high frequency and high energy are mutually exclusive problems, because the PIV light source system has a power limit, that is, the product of pulse energy E and pulse frequency f cannot exceed the upper limit value, otherwise it will cause the laser to overheat and burn out the laser components in a short time. SUMMARY

[0003] Based on the above shortcomings, the purpose of the present application is to provide a fixed frequency and variable frequency multi-pulse laser device, which can generate high frequency multi-pulse laser.

[0004] The technical scheme adopted by the present application is as follows: a kind of fixed frequency and variable frequency multi-pulse laser device, including three polarizers, four dichroic mirrors, a reflecting mirror and four groups of cavities, each group of cavities includes rear mirror, electro-optic Q switch and crystal, the crystal is diode pumped Nd:YAG crystal, first electro-optic Q open light of first cavity is opened after emitting pulsed laser signal, first laser beam is formed by first crystal, first laser beam is split by first polarizer, part is collected by first absorption box, another part converges to the second polarizer of second cavity;After interval time dt1, second electro-optic Q switch of second cavity is opened after emitting pulsed laser signal, second laser beam is formed by second crystal, after second laser beam is split by second polarizer, it is coincident with first laser beam by first beam combination module, after second laser beam is coincident, part is collected by second absorption box, another part converges to the second dichroic mirror, after interval time dt2, third electro-optic Q switch of third cavity is opened after emitting pulsed laser signal, third laser beam is formed by third crystal, after third laser beam is split by second dichroic mirror, it is coincident with the laser that first dichroic mirror changes light path by second beam combination module, after third laser beam is coincident, part is collected by third absorption box, another part converges to the fourth dichroic mirror, after interval time dt3, fourth electro-optic Q switch of fourth cavity is opened after emitting pulsed laser signal, fourth laser beam is formed by fourth crystal, after fourth laser beam is split by fourth dichroic mirror and the laser that third dichroic mirror changes light path passes through third beam combination module, after fourth laser beam is coincident, it is split by first polarizer, one way is guided out by first reflecting head, another way is guided out by second reflecting head after the direction of propagation is changed by reflecting mirror;Wherein, after first cavity emits first pulsed laser, after interval time dt1, second cavity emits second pulsed laser, then after interval time dt2, third cavity emits third pulsed laser, then after interval time dt3, fourth cavity emits fourth pulsed laser, repeat this process to form multi-pulse laser, wherein interval time dt1 is equal to interval time dt3, interval time dt2 can be continuously adjustable, to form fixed frequency and variable frequency multi-pulse laser.

[0005] Further, the first and second polarizers are 1064nm polarizers, and the third polarizer is a 532nm polarizer.

[0006] Further, the reflecting mirror is a 532nm, 45° reflectivity reflecting mirror.

[0007] Further, the first, second, third and fourth dichroic mirrors are 1064nm transmittance, 532nm, 45° reflectivity dichroic mirrors.

[0008] Further, the crystal is a diode pumped Nd:YAG crystal capable of forming a 532nm laser beam.

[0009] Further, the adjustable range of the laser device is 1 / 2000s-1 / 200s,

[0010] The application has the advantages and beneficial effects that the application can obtain the output of the pulse light source with high repetition frequency, high energy and high average power, the laser device has multi-path beam combination, the energy of each laser is 400mJ, has double light output capacity, the energy proportion of the light path is adjustable, the wavelength of the laser is 532nm, the overall frequency of the pulse laser is 200Hz, the local frequency of the pulse laser is 2000Hz at most, the adjustable range is 200Hz-2000Hz, and the step is 10Hz. The device of the application can obtain multiple trigger laser distribution results with adjustable time interval in a single sampling period, and further realizes the measurement of the flow field with high time resolution and improves the test efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 The laser device of the application;

[0012] Figure 2 The multi-path beam combination light path design of the laser device of the application;

[0013] Figure 3 The working schematic diagram of the laser device of the application. DETAILED DESCRIPTION

[0014] In order to make the technical means, creative features, purposes and effects of the application easy to understand, the application is further described below in combination with specific embodiments, but the following embodiments are only preferred embodiments of the application, not all.

[0015] Embodiment 1:

[0016] As Figures 1-2The illustrated fixed frequency and variable frequency multi-pulse laser device includes three polarizers, four dichroic mirrors, a reflector and four sets of cavities, each set of cavity including a back mirror, an electro-optical Q switch and a crystal, the crystal being a diode pumped Nd:YAG crystal capable of forming a 532nm laser beam, the first electro-optical Q switch 6 of the first cavity 1 being turned on to emit a pulsed laser signal, the first laser beam being formed by the first crystal 7, the first laser beam being split by the first polarizer 8, a part of which is collected by the first absorption box 9, and the other part converging on the second polarizer 13 of the second cavity 2; after a time interval dt1, the second electro-optical Q switch 11 of the second cavity 2 is turned on to emit a pulsed laser signal, the second laser beam being formed by the second crystal 12, the second laser beam being split by the second polarizer 13 and coinciding with the first laser beam after passing through the first beam combining module 14, the coincided second laser beam passing through the first dichroic mirror 15, a part of which is collected by the second absorption box 16, and the other part converging on the second dichroic mirror 20, after a time interval dt2, the third electro-optical Q switch 18 of the third cavity 3 is turned on to emit a pulsed laser signal, the third laser beam being formed by the third crystal 19, the third laser beam being split by the second dichroic mirror 20 and coinciding with the laser beam changing its path after passing through the first dichroic mirror 15 by passing through the second beam combining module 21, the coincided third laser beam passing through the third dichroic mirror 22, a part of which is collected by the third absorption box 23, and the other part converging on the fourth dichroic mirror 27, after a time interval dt3, the fourth electro-optical Q switch 25 of the fourth cavity 4 is turned on to emit a pulsed laser signal, the fourth laser beam being formed by the fourth crystal 26, the fourth laser beam being split by the fourth dichroic mirror 27 and coinciding with the laser beam changing its path after passing through the third dichroic mirror 22 by passing through the third beam combining module 28, the coincided fourth laser beam being split by the third polarizer 29, one way being guided out by the first reflection head 32, and the other way being guided out by the second reflection head 31 after changing its path by the reflector 30; wherein, after the first cavity 1 emits the first pulsed laser, after a time interval dt1, the second cavity 2 emits the second pulsed laser, then after a time interval dt2, the third cavity 3 emits the third pulsed laser, and then after a time interval dt3, the fourth cavity 4 emits the fourth pulsed laser, and the process is repeated to form a multi-pulse laser, wherein the time interval dt1 is equal to the time interval dt3, and the time interval dt2 is continuously adjustable to form a fixed frequency and variable frequency multi-pulse laser. The first and second polarizers are 1064nm polarizers, and the third polarizer is a 532nm polarizer. The reflector is a 532nm, 45° reflectivity reflector. The first, second, third and fourth dichroic mirrors are 1064nm transmittance, 532nm, 45° reflectivity dichroic mirrors.

[0017] As Figure 3As shown, four cavities can generate four pulse lasers in one cycle. The first and second cavities generate laser time difference is dt1, the second and third cavities generate laser time difference is dt2, and the third and fourth cavities generate laser time difference is dt3. In this process, dt1 and dt3 are equal, and dt2 can be adjusted. The first cavity twice exposure time difference is 1 / 200s, and the adjustable range of dt2 is 1 / 2000s-1 / 200s, to form a fixed frequency and variable frequency multi-pulse laser device. By using the device, it can be used for measuring the flow field velocity field with the overall frequency of 200Hz and the local maximum frequency of 2000Hz. In summary, the application can obtain multiple trigger laser distribution results with adjustable time interval in a single sampling cycle, and further realizes the measurement of high time resolution of the flow field.

Claims

1. A fixed-frequency and variable-frequency multi-pulse laser device, comprising three polarizers, four dichroic mirrors, a reflector, and four sets of cavities, each set of cavities comprising a rear mirror, an electro-optic Q-switch, and a crystal, wherein the crystal is a diode-pumped Nd:YAG crystal, characterized in that: After the first electro-optic Q switch (6) of the first cavity (1) is turned on, it emits a pulsed laser signal, which forms a first laser beam through the first crystal (7). The first laser beam is split by the first polarizer (8), and part of it is collected by the first absorption box (9), while the other part is focused onto the second polarizer (13) of the second cavity (2). After an interval of time dt1, the second electro-optic Q switch (11) of the second cavity (2) is turned on, and it emits a pulsed laser signal, which forms a second laser beam through the second crystal (12). The second laser beam is split by the second polarizer (13) and then merges with the first laser beam. The laser beams are combined by the first beam combining module (14). The combined second laser beam passes through the first dichroic mirror (15), part of which is collected by the second absorber (16), and the other part is focused onto the second dichroic mirror (20). After an interval of time dt2, the third electro-optic Q switch (18) of the third cavity (3) is turned on and emits a pulsed laser signal. The pulsed laser signal is formed by the third crystal (19). The third laser beam is split by the second dichroic mirror (20) and then combined with the laser beam that has changed its optical path from the first dichroic mirror (15) through the second beam combining module (21). The combined third laser beam passes through the third dichroic mirror (22), part of which is collected by the third absorber (23), and the other part is focused onto the fourth dichroic mirror (27). After an interval of dt3, the fourth electro-optic Q switch (25) of the fourth cavity (4) is turned on and emits a pulsed laser signal. The fourth laser beam is formed through the fourth crystal (26). The fourth laser beam is split by the fourth dichroic mirror (27) and merges with the laser beam that has changed its optical path by the third dichroic mirror (22) through the third beam combining module (28). The merged fourth laser beam passes through the third polarizer (29). The light is split, with one path leading out from the first reflector (32) and the other path leading out from the second reflector (31) after the reflector (30) changes the direction of light propagation. After the first cavity (1) emits the first pulse laser, the second cavity (2) emits the second pulse laser after an interval of dt1, and then the third cavity (3) emits the third pulse laser after an interval of dt2. After an interval of dt3, the fourth cavity (4) emits the fourth pulse laser. This process is repeated to form a multi-pulse laser. The interval dt1 is equal to the interval dt3, and the interval dt2 can be continuously adjusted to form fixed-frequency and variable-frequency multi-pulse lasers.

2. The fixed-frequency and variable-frequency multi-pulse laser device according to claim 1, characterized in that: The first and second polarizers are 1064 nm polarizers, and the third polarizer is a 532 nm polarizer.

3. The fixed-frequency and variable-frequency multi-pulse laser device according to claim 1, characterized in that: The reflector is a reflector with a wavelength of 532 nm and an incident angle of 45°.

4. The fixed-frequency and variable-frequency multi-pulse laser device according to claim 1, characterized in that: The first, second, third, and fourth dichroic mirrors are dichroic mirrors with two wavelengths of 1064 nm and 532 nm and an incident angle of 45°.

5. A fixed-frequency and variable-frequency multi-pulse laser device according to claim 1, characterized in that: The crystal is a diode-pumped Nd:YAG crystal capable of forming a 532 nm laser beam.

6. A fixed-frequency and variable-frequency multi-pulse laser device according to any one of claims 1-5, characterized in that: The laser emission interval of the laser device is adjustable in the range of 1 / 2000 s to 1 / 200 s.

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