WO2014067184A1

WO2014067184A1 - Apparatus based on four-quadrant detector and for measuring flow field in cavity of pulsed gas laser

Info

Publication number: WO2014067184A1
Application number: PCT/CN2012/084929
Authority: WO
Inventors: 徐勇跃; 杨晨光; 左都罗; 王新兵; 卢宏; 陆培祥
Original assignee: 华中科技大学
Priority date: 2012-10-30
Filing date: 2012-11-21
Publication date: 2014-05-08
Also published as: CN102980739A; CN102980739B

Abstract

An apparatus based on a four-quadrant detector and for measuring the flow field in a cavity of a pulsed gas laser comprises a detection light source (1), a detection light receiving system, and a signal processing system. The light beam emitted by the detection light source (1) is parallel with the optical axis direction of the pulsed gas laser. The detection light receiving system comprises a four-quadrant photoelectric detector (4); a photosensitive side thereof faces a detected area, is perpendicular to the detection light beam, and is used for receiving a detection laser beam; after a signal of the four-quadrant photoelectric detector (4) is processed by the signal processing system, propagation characteristics parameters of the shock wave is obtained. The measurement device is of a simple structure, and is easy to operate. The measurement apparatus simplifies the experiment apparatus by using the four-quadrant photoelectric detector (4), and determines the disturbance and propagation direction of the shock wave according to the moving of the light spot center of the four-quadrant photoelectric detector, which improves the detection sensitivity; meanwhile, separates the detection light beam from the laser of the pulsed gas laser by using a dichroic mirror (2), and obtains the real-time test result during laser oscillation, thereby overcoming the defect of high thermal deposition in testing the discharge area without the use of the laser resonator.

Description

Pulse gas laser intracavity flow field measuring device based on four-quadrant detector [Technical Field]

The invention belongs to the technical field of optical measurement, and relates to a device for measuring fluctuation of a flow field, in particular to a device for measuring shock propagation characteristics in a flow field based on a four-quadrant photodetector, using quadrants of four-quadrant photodetectors The output change realizes the measurement of the direction of propagation of the shock wave and its disturbance. This method is especially suitable for the measurement of gas flow field disturbances in pulsed gas lasers.

【Background technique】

Pulsed gas lasers with pulsed discharge pumping have been widely used in the industry for high repetition rate, high energy and low cost, such as integrated circuit lithography, laser medical treatment and industrial processing. During the operation of the pulsed gas laser, since the instantaneous injection energy is large in a limited space, shock waves developed in different directions are generated, and these shock waves reciprocate back and forth in the laser cavity, and the density changes during the propagation process. The uniformity of the excitation medium in the cavity is changed, so the disturbance magnitude of the shock wave characterizes the uniformity of the flow field. Since the non-uniformity of the flow field in the laser cavity directly affects the uniformity of the discharge, which in turn affects the beam quality of the laser output and the stability of the output power, the measurement of the shock characteristic parameters (including the magnitude and propagation direction of the shock wave) It is especially important.

Traditional methods of measuring flow field fluctuations often use the pressure probe method. Uteza, Ph.

Delaporte, B. Fontaine, B. Forestier, M. Sentis, I. Tassy, J.P. Truong: Appl. Phys. B 64, 531 (1997);, This method uses a piezoelectric transducer to stress the flow field The fluctuation is converted into an electrical signal output, and the disturbance amount in the flow field can be monitored in real time. This method belongs to a contact type measurement and needs to be mounted on the inner wall of the laser cavity. It cannot be moved freely. It is difficult to achieve precise positioning during measurement, and the method cannot judge the source and propagation characteristics of the disturbance.

Interferometry and schlieren are two commonly used non-contact measurement methods for observing the development of shock waves in pulsed gas lasers (V. Delaporte, B. Fontaine, B. Forestier, M. Sentis, J. P. Truong)

O. Uteza, D. Zeitoun, D. Tarabelli: Proc. 18th Int. Symp. Shock Waves 2, 1301 (1991); Dry The optical system of the related law obtains the information of the change of the gas density caused by the shock wave in the flow field through the change of the interference fringes on the receiving screen, thereby judging the magnitude and the propagation direction of the shock disturbance. Similarly, the schlieren optical system can convert the density disturbance information caused by the shock into a change in the intensity of the receiving screen, and determine the position and direction of the shock by the change of the intensity. Both methods can intuitively obtain the situation in the flow field by receiving the change information of the light distribution on the screen, and determine the origin and development process of the shock wave. However, both methods use time series method to capture the evolution of the flow field at different moments of different pulses, and the evolution process of the shock wave in the combined flow field can not obtain real-time signals; and the two system devices are compared. Complex and need more precision optical equipment, operation and data processing are more troublesome. Wingate et al. used a single-point schlieren method to measure the shock intensity in the flow field after pulsed discharge of a pulsed gas laser. Wingate, JT Lee, AIAA Paper 81-1286 (1981). Wave disturbance, but this method cannot accurately detect the direction of shock wave propagation.

[Summary of the Invention]

The object of the present invention is to provide a measuring device for shock waves in a flow field of a pulsed gas laser, which can easily and accurately measure the magnitude of the shock disturbance and the propagation direction in the flow field of the pulsed gas laser, and the subsequent processing of the signal is relatively simple. .

The invention provides a four-quadrant detector-based pulse gas laser intracavity flow field measuring device, which comprises a detecting light source, a detecting light receiving system and a signal processing system, characterized in that: the light beam emitted by the detecting light source and the light of the pulse gas laser are detected. The axial direction is parallel; the detecting light receiving system comprises a four-quadrant photodetector, wherein the photosensitive surface of the four-quadrant photodetector faces the detecting area and is perpendicular to the detecting beam for receiving the detecting laser beam emitted by the detecting light source; four-quadrant photoelectric detecting The signal of the device is processed by the signal processing system to obtain the propagation characteristic parameters of the shock wave.

As an improvement of the above technical solution, the probe light receiving system further includes a two-color mirror and a laser line filter, wherein the two-color mirror is at 45 degrees with the probe beam, and the filter and the four-quadrant photodetector face the probe beam. The detecting light source, the dichroic mirror, the laser line filter and the four-quadrant photodetector are sequentially located on the same optical path. As another improvement of the above technical solution, the probe light receiving system further includes a two-color mirror, a laser line filter, and a beam splitter, wherein the split mirror surface and the two-color mirror surface are at an angle of 45 degrees with the probe beam, and the laser line filter The slice is perpendicular to the probe beam, and the probe beam passes through the center of the spectroscopic surface and the dichroic mirror, respectively, and is reflected by the reflection surface of the laser to be tested, and then passes through the center of the dichroic mirror and the spectroscopic mirror and the center of the laser line filter, and finally by the four quadrants. The detector receives.

The invention overcomes the shortcomings of the traditional measuring device system and the expensive equipment, and improves the precision and sensitivity of the measurement, and can obtain the disturbance magnitude and the propagation direction of the shock wave in the flow field in real time. When the pulsed gas laser is working, a large amount of energy is instantaneously injected into the flow field after each discharge excitation, and various shock waves are formed in the flow field. These shock waves have a wavefront in a high-density region, which causes the probe beam to be generated. The deflection occurs, and the change of each quadrant output obtained by the four-quadrant photodetector is used to process and display the spot shift information by the data acquisition circuit, and the offset of the spot center and the propagation characteristics of the shock wave exist. The specific relationship is the magnitude of the disturbance and the direction of propagation.

The invention has the advantages of simple structure and convenient operation, and the four-quadrant photodetector greatly simplifies the experimental device, and determines the disturbance magnitude and propagation direction of the shock wave through the movement of the center of the four-quadrant photodetector spot, thereby improving the sensitivity of the detection; The mirror separates the probe beam from the laser of the pulsed gas laser, and the laser oscillation simultaneously obtains real-time test results, avoiding the defect of high thermal deposition in the discharge region when no laser cavity is tested.

[Description of the Drawings]

Figure 1 is a schematic structural view of the present invention;

2 is an example of the invention applied to the direction in which the probe beam is in the same direction as the exit direction of the pulsed gas laser;

3 is an example of a pulse gas laser applied to a rear mirror full-reverse; FIG. 4 is a cross-sectional view of a four-quadrant photodetector used in the present invention;

Figure 5 is a working flow chart of the present invention;

Figure 6 shows the experimental results simulated with Matlab software. [specific lung type]

The wave array composed of high-density regions corresponding to various shock waves formed by the pulsed gas laser propagates to the periphery, forming a density disturbance region during the propagation process; the light beam propagates in the non-uniform medium and is biased toward the region with high density. Fold, the size of the deflection is proportional to the density gradient, and the deflection direction is the same as the normal direction of the shock wave front. Therefore, the size of the spot offset can be used to characterize the density disturbance caused by the shock, and the angle of the spot shift To determine the direction of the shock wave. The four-quadrant photodetector can record the change of the offset of the center position of the detection spot with time in real time. The magnitude and propagation direction of the shock wave in the flow field of the pulsed gas laser can be obtained by the magnitude and angle of the offset.

The present invention has been designed based on the above principles, and the specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings. It is to be noted that the description of the embodiments is intended to aid the understanding of the invention and is not intended to limit the invention. Further, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not constitute a conflict with each other. As shown in FIG. 1 , the measuring device for the shock wave in the pulse gas laser provided by the present invention mainly comprises a detecting light source 1, a dichroic mirror 2, a laser line filter 3, a four-quadrant photodetector 4, a data collecting circuit 5 and a computer. 6. The two-color mirror 2, the laser line filter 3 and the four-quadrant photodetector 4 constitute a photoelectric receiving portion, and the data collecting circuit 5 passes the output signal in the four-quadrant photodetector 4 to the computer 6 for processing and display. The size and direction of the wave.

The direction in which the light source 1 emits the light beam is parallel to the direction of the optical axis generated by the pulsed gas laser. As shown in FIG. 2, the laser wavelength of the detecting light source 1 is selected so as to be transmitted through the rear mirror 11 and the output window of the pulsed gas laser 10. 12. The transmitted beam does not affect the laser oscillation of the pulsed gas laser; the spot diameter and divergence angle of the beam should be small, ensuring that the spot diameter in the detection area is less than 1 mm, improving the detection accuracy; detecting light source 1 and four-quadrant photoelectricity The detectors 4 can be controlled together by a two-dimensional translation stage to detect real-time shock surges at different locations in the pulsed gas laser flow field. 2 is that the rear mirror 11 and the output window 12 are both transparent to the detection beam, If the mirror 21 of the pulsed gas laser 20 is opaque, but the output window 22 is transparent, the device can be replaced with the device shown in FIG. 3, wherein the beam splitter 23 functions to be semi-transverse to the probe beam; The output window 22 enters, is reflected by the rear mirror 21, is still separated by the output window 22, passes through the dichroic mirror 2, and the beam splitter 23, and then passes through the laser line filter 3 to the four-quadrant photodetector 4.

The dichroic mirror 2 is at 45° to the optical axis of the pulsed gas laser, and the dichroic mirror 2 is a narrowband reflective filter. The center wavelength of the reflection is the output wavelength of the laser, and the full width at half maximum (FWHM) of the reflection is less than lOnm; The laser beam is reflected to enable other wavelengths of light to pass through, that is, the laser radiation of the pulsed gas laser is highly reflected, but the reflection of the light emitted by the detecting light source is low, which makes the measuring device not to pulse gas during the test. The working state of the laser and the optical path have an effect, and the laser radiation of the pulsed gas laser is also prevented from being destroyed by the four-quadrant detector; the laser line filter 3 is a narrow-band transmission filter whose transmitted central wavelength is the wavelength emitted by the detecting light source. The transmitted full-width half-peak width (FWHM) is less than 5 nm, that is, it can only filter the light emitted by the light source 1 and filter out other wavelengths of light; thereby further reducing the influence of other factors on the detector.

The four-quadrant photodetector 4 has four symmetrical photosensitive surfaces, as shown in FIG. Before the measurement, the position and angle of the four-quadrant photodetector 4 need to be fine-tuned so that the spot emitted by the detecting light source 1 is evenly distributed in four quadrants. The four-quadrant photodetector 4 has a response frequency of several tens of megahertz and a shock perturbation period of a few microseconds, thus meeting the needs of real-time detection. The filter in the optical path only passes the probe light, which prevents the laser of the pulsed gas laser from damaging the four-quadrant photodetector.

The data acquisition circuit 5 includes a preamplifier, an A/D conversion circuit, etc., which inputs the photoelectric signal to the computer 6 for processing and display, and obtains the spot center offset information; further obtains the beam deflection law caused by the shock wave propagation process. The magnitude and direction of the wave disturbance, where the magnitude of the offset characterizes the intensity of the shock, and the angle of the offset determines the direction of propagation of the shock.

Next, the operation flow of the pulse gas laser flow field shock measuring apparatus of the present invention will be described with reference to FIG. Before the pulse gas works, the moving detecting light source 1 is placed at the position to be detected, and the position of the four-quadrant photodetector 4 is adjusted accordingly, so that the spot emitted by the detecting light source 1 passes through the flow field of the pulsed gas laser, and is evenly distributed in four. Four quadrants of the quadrant photodetector 4. After the pulsed gas laser is pulsed, a strong electromagnetic interference of several tens of nanoseconds is generated, which acts as a trigger signal for the four-quadrant photodetector 4.

Pulse excitation is accompanied by a large amount of energy deposition. In the flow field of a pulsed gas laser, a lot of shock waves are generated. These shock waves diffuse and spread around, and when the light is detected, they are deflected and the center of the spot is moved. The output of the four quadrants of quadrant photodetector 4 changes. Let the voltages generated in the one to four quadrants be

Then the offset of the spot in the horizontal and vertical directions is:

Where k is a fixed parameter of the four-quadrant photodetection, reflecting the relationship between the amount of change in light intensity and the amount of movement of the spot position, which can be obtained by calibrating the detector. Spot size and offset angle can be obtained by (1)

When the shock wave is close to the probe beam, the probe beam is deflected toward the shock wave. The direction of the offset is opposite to the normal direction of the wavefront. When the shock wave passes through the probe beam, the probe beam is also deflected toward the shock wave. The direction is the same as the normal direction of the wavefront. Therefore, when the shock wave passes through the probe beam, the deflection angle of the light remains constant. However, when the shock wave approaches and stays away, the deflection angle of the light will be different by 180°, and the direction of the shock wave propagation and the deflection angle of the light wave caused by the shock wave are far away. equal. Since the high-density wavefront formed by the shock has a certain width, the output signal that evolves over time can be detected, and thus the real-time information of the spot shift is obtained. Spot shift at different times t when the shock passes through the probe beam ρ ) and the spot deflection angle e( _t ) can be expressed by the following formula:

Figure 6 shows the real-time change information of the spot shift amount and the spot deflection angle caused by the Matlab software simulating the shock wave propagating in the 45° direction through the probe beam. The magnitude of the shock disturbance is P( _t)max. The direction of the shock wave is the same as the angle at which the shock wave leaves the probe beam, that is, the same as the second half of the result of the angle deviation of the spot, and propagates in the direction of 45°. Since the four-quadrant photodetector 4 has a high detection frequency, it can reflect the evolution of the shock wave in the flow field in real time, and observe the magnitude and direction of the shock disturbance in the flow field.

The invention can well detect the shock wave in the laser cavity, can accurately determine the size and propagation direction of the shock wave, and has higher sensitivity, simple measuring device and simple method.

The above is a preferred embodiment of the present invention, but the present invention should not be limited to the contents disclosed in the embodiment and the drawings. Therefore, equivalents or modifications made without departing from the spirit of the invention are intended to fall within the scope of the invention.

Claims

claims

1. A pulsed gas laser intracavity flow field measurement device based on a four-quadrant detector, including a detection light source, a detection light receiving system and a signal processing system, which is characterized in that: the light beam emitted by the detection light source is in the same direction as the optical axis of the pulse gas laser Parallel; The detection light receiving system includes a four-quadrant photodetector, in which the photosensitive surface of the four-quadrant photodetector faces the detection area and is perpendicular to the detection beam, and is used to receive the detection laser beam emitted by the detection light source; After the signal is processed by the signal processing system, the propagation characteristic parameters of the shock wave are obtained.

2. The pulsed gas laser cavity flow field measurement device based on a four-quadrant detector according to claim 1, characterized in that the detection light receiving system also includes a dichromatic mirror and a laser line filter, and the dichromatic The mirror plane is 45 degrees to the detection beam. The filter and the four-quadrant photodetector are facing the detection beam. The detection light source, dichroic mirror, laser line filter and four-quadrant photodetector are located on the same optical path in sequence.

3. The pulsed gas laser cavity flow field measurement device based on a four-quadrant detector according to claim 1, characterized in that the detection light receiving system also includes a dichroic mirror, a laser line filter and a spectroscope, so The spectroscopic mirror, the two-color mirror and the detection beam are at an angle of 45 degrees, the laser line filter is perpendicular to the detection beam, the detection beam passes through the center of the spectrometry mirror and the two-color mirror respectively, and is reflected by the reflective surface of the laser under test before passing through again The centers of the dichroic mirror and beam splitter mirror and the center of the laser line filter are finally received by the four-quadrant detector.

4. The pulsed gas laser cavity flow field measurement device based on a four-quadrant detector according to claim 2 or 3, characterized in that the laser line filter is a narrow-band transmission filter that is highly transparent to the detection laser beam.

5. The pulsed gas laser cavity flow field measurement device based on a four-quadrant detector according to claim 2 or 3, characterized in that the dichroic mirror is a narrow-band reflection filter that highly reflects the pulsed laser beam.

6. Intra-cavity flow of pulsed gas laser based on four-quadrant detector according to claim 4 The field measurement device is characterized in that the dichromatic mirror is a narrow-band reflection filter that highly reflects the pulsed laser beam.

7. The pulsed gas laser cavity flow field measurement device based on a four-quadrant detector according to claim 2 or 3, characterized in that the spectroscope is a filter that is semi-transparent and semi-reflective to the detection light.