CN101949871B - Device for measuring thermal power of nonlinear crystal - Google Patents

Abstract

The invention discloses a device for measuring the thermal power of a nonlinear crystal, which comprises a nonlinear crystal, a temperature sensor, an intelligent module, a temperature control power supply, a temperature control furnace and an oscilloscope. The nonlinear crystal is placed inside the temperature control furnace and works at a certain set temperature T ₁ to play the role of laser frequency conversion; the temperature sensor is used to measure the actual working temperature T ₀ of the nonlinear crystal and feed back the value For the intelligent module; the intelligent module is used to compare the actual working temperature T ₀ of the nonlinear crystal measured by the temperature sensor with the set temperature T ₁ , and adjust the heating voltage output by the temperature control power supply to the temperature control furnace accordingly, and convert the nonlinear crystal to the temperature control furnace. The crystal is controlled at the set working temperature T ₁ ; the temperature control furnace uses heating wire as the heating element; the temperature sensor, the intelligent module, the temperature control power supply and the temperature control furnace constitute the temperature control system, and the oscilloscope measures the temperature control power supply to the temperature control furnace in real time. The waveform W of the output heating voltage. Utilizing the invention, the measurement of the thermal power of the nonlinear crystal is realized.

Description

A device for measuring thermal power of nonlinear crystal

technical field

The invention relates to the field of laser technology, in particular to a device for measuring the thermal power of a nonlinear crystal, which is generated by the nonlinear crystal due to the absorption of laser light.

Background technique

Nonlinear crystals can convert fundamental frequency light of a certain wavelength into laser light of other wavelengths, which greatly expands the wavelength range of laser light, thereby expanding the application range of laser light. For example, LBO crystal can double the frequency of 1064nm infrared laser to 532nm green light, and PPLN crystal can convert 1064nm laser into mid-infrared laser with tunable wavelength. Therefore, nonlinear crystals play a very important role in laser systems. When working, the nonlinear crystal has a very small absorption coefficient for the laser light passing through it, and basically does not absorb the laser light.

However, under high-power working conditions, such as when the LBO crystal doubles the frequency of 1064nm laser to produce high-power green light, the power of the fundamental-frequency pump light is very high, and the LBO crystal absorbs the fundamental-frequency light to generate a certain amount of thermal power, which causes the temperature of the crystal to rise. high, resulting in phase mismatch and lower conversion efficiency; another example, in the 1064nm laser-pumped optical parametric oscillator based on periodically polarized magnesium oxide-doped lithium niobate (PPMgLN-OPO), in order to reduce the pump light The threshold power of the OPO cavity mirror, the input mirror and the output mirror of the OPO cavity mirror are highly reflective to the oscillating light (such as signal light), so the power of the oscillating light circulating in the cavity is very high. The PPMgLN crystal will generate thermal power due to the absorption of oscillating light in the cavity, which will cause the temperature of the crystal to rise and cause a thermal effect, thereby reducing the parametric conversion efficiency and the beam quality of the output laser.

It can be seen that the phenomenon that nonlinear crystals absorb laser light and generate thermal power has a great influence on the nonlinear conversion process, and it is very important to study this phenomenon in detail. Measuring the thermal power generated by nonlinear crystals absorbing laser light can determine the degree of thermal effects generated by crystals in the nonlinear process, and further optimize the experimental design, which is a very important research topic.

At present, there are not many methods for measuring the thermal power generated by nonlinear crystals absorbing laser light. A.Henderson et al. (Appl.Phys.B, vol(85), 2006: 181-184) in the PPLN-OPO experiment, first measured the transmittance of the OPO cavity mirror at the wavelength of the signal light (oscillating light) through experiments, and then Calculate the power of the circulating signal light in the cavity according to the signal light power output by the OPO cavity, and then calculate the thermal power generated by the crystal absorbing the signal light according to the absorption coefficient of the PPLN crystal used for the signal light at this wavelength. The process of this method is cumbersome, and only the power of the crystal absorbing signal light of a specific wavelength can be obtained at one time. If the OPO is tuned to change the wavelength of the signal light, then the transmittance of the OPO cavity mirror at this wavelength must be re-measured. In addition, if the PPLN crystal also absorbs the pump light and idler light output by the OPO, it is not easy to measure the thermal power generated by the laser absorption by using this method.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide a device for measuring the thermal power of a nonlinear crystal.

(2) Technical solution

In order to achieve the above object, the present invention provides a device for measuring the thermal power of a nonlinear crystal, which includes a nonlinear crystal 101, a temperature sensor 102, an intelligent module 103, a temperature control power supply 104, a temperature control furnace 105 and an oscilloscope 106, in:

The nonlinear crystal 101 is placed inside the temperature control furnace 105 and works at a certain set temperature _T1 to play the role of laser frequency conversion;

The temperature sensor 102 is used to measure the actual working temperature T ₀ of the nonlinear crystal 101, and feed this value back to the intelligent module 103;

The intelligent module 103 is used to compare the actual working temperature _T0 of the nonlinear crystal 101 measured by the temperature sensor 102 with the set temperature _T1 , adjust the heating voltage output from the temperature control power supply 104 to the temperature control furnace 105 accordingly, and set The nonlinear crystal 101 is controlled at a set working temperature _T1 ;

The temperature control furnace 105 adopts a heating wire as a heating element;

The temperature sensor 102, the intelligent module 103, the temperature control power supply 104 and the temperature control furnace 105 constitute the temperature control system 001, and the oscilloscope 106 measures the waveform W of the heating voltage output from the temperature control power supply 104 to the temperature control furnace 105 in real time.

In the above scheme, when the nonlinear crystal 101 is not subjected to laser frequency conversion, in order to maintain the nonlinear crystal 101 at the set operating temperature _T1 , the temperature control power supply 104 needs to output a certain amount of heating to the temperature control furnace 105. Voltage, the oscilloscope 106 records the heating voltage waveform W ₁ output from the temperature control power supply 104 to the temperature control furnace 105 within a period of time t, and the temperature control can be calculated according to the heating voltage waveform W ₁ and the resistance value of the heating resistance wire inside the temperature control furnace 105. The heating electric power generated by the furnace 105 is _P1 ; when the nonlinear crystal 101 performs laser frequency conversion, in order to maintain the nonlinear crystal 101 at the set operating temperature _T1 , the temperature control power supply 104 needs to be supplied to the temperature control The furnace 105 outputs different heating voltages, and the oscilloscope 106 records the voltage waveform W ₂ output from the temperature control power supply 104 to the temperature control furnace 105 within a period of time t in this case. According to the voltage waveform W ₂ and the internal heating resistance wire of the temperature control furnace 105 Calculate the heating electric power P ₂ generated by the temperature control furnace 105 from the resistance value.

In the above scheme, there is a difference between the heating electric power P ₁ and P ₂ generated by the temperature control furnace 105, and the difference P ₁ -P ₂ is the result of the nonlinear crystal 101 absorbing the laser light during the laser frequency conversion process. The amount of thermal power generated.

In the above solutions, the nonlinear crystal 101 includes PPLN, PPKTP, PPLT, KTP, LBO or BBO crystals.

In the above solution, the laser frequency conversion process performed by the nonlinear crystal 101 includes optical parametric oscillation, frequency doubling and frequency summing.

In the above solution, the laser light absorbed by the nonlinear crystal 101 during laser frequency conversion is fundamental frequency light or frequency conversion light.

(3) Beneficial effects

Compared with the prior art, the present invention has the following advantages and positive effects:

1. The method for measuring the thermal power produced by nonlinear crystals absorbing laser light provided by the present invention only needs to add an oscilloscope on the basis of the original temperature control system to complete the measurement, which has the advantage of convenient operation.

2. The method for measuring the thermal power generated by the nonlinear crystal absorbing laser light provided by the present invention only needs to calculate the heating electric power P1 generated by the temperature control furnace when the nonlinear crystal is not subjected to laser frequency conversion and laser frequency conversion is performed respectively. and P2, the thermal power (P1-P2) generated by the nonlinear crystal absorbing the laser can be obtained, which has the advantage of simple calculation.

3. The method for measuring the thermal power generated by the nonlinear crystal absorbing laser light provided by the present invention, no matter how much the wavelength of the laser light absorbed by the nonlinear crystal during the laser frequency conversion process is, or the absorption coefficient of the nonlinear crystal for laser light is How much, or the nonlinear crystal absorbs the fundamental frequency light or the frequency conversion light, using this method can easily measure the thermal power generated by the nonlinear crystal absorbing laser light, and has the advantage of a wide range of applications.

Description of drawings

In order to further illustrate the specific technical content of the present invention, below in conjunction with embodiment and accompanying drawing detailed description as follows, wherein:

Fig. 1 is the schematic diagram of the device for measuring the size of the thermal power generated by the nonlinear crystal due to the absorption of laser light provided by the present invention;

Fig. 2 is a schematic diagram of measuring the thermal power generated by the nonlinear crystal PPMgLN absorbing laser light in the PPMgLN-OPO experiment using the device for measuring the thermal power generated by the nonlinear crystal absorbing the laser light provided by the present invention;

3 is a schematic diagram of the heating voltage waveform W1 output by the temperature control power supply 204 to the temperature control furnace 205 using an oscilloscope 206 when the PPMgLN crystal is not subjected to laser frequency conversion;

4 is a schematic diagram of the heating voltage waveform W2 output by the temperature control power supply 204 to the temperature control furnace 205 using an oscilloscope 206 when the PPMgLN crystal is subjected to laser frequency conversion;

Fig. 5 is a schematic diagram of measurement results of thermal power generated by PPMgLN crystals absorbing laser light under different pump power conditions.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

As shown in Figure 1, Figure 1 is a schematic diagram of a device for measuring the thermal power generated by a nonlinear crystal due to the absorption of laser light provided by the present invention. The device includes: a nonlinear crystal 101, a temperature sensor 102, an intelligent module 103, a temperature control Power supply 104, temperature control furnace 105 and oscilloscope 106. The nonlinear crystal 101 is placed inside the temperature control furnace 105 and works at a certain set temperature T ₁ to play the role of laser frequency conversion. The temperature sensor 102 is used to measure the actual working temperature T ₀ of the nonlinear crystal 101 and feed back the value to the intelligent module 103 . The intelligent module 103 compares the actual working temperature _T0 of the nonlinear crystal 101 measured by the temperature sensor 102 with the set temperature _T1 , and adjusts the heating voltage output by the temperature control power supply 104 to the temperature control furnace 105 accordingly, by This achieves the effect of controlling the nonlinear crystal 101 at the set operating temperature _T1 . The temperature sensor 102 , intelligent module 103 , temperature control power supply 104 and temperature control furnace 105 constitute a temperature control system 001 . The oscilloscope 106 measures the waveform W of the heating voltage output from the temperature control power supply 104 to the temperature control furnace 105 in real time. The effective value of the heating voltage output by the temperature control power supply 104 to the temperature control furnace 105 is U=24V. The inside of the temperature control furnace 105 uses a constantan wire with a resistance value of R=34Ω as a heating wire. The temperature sensor 102 uses a Pt100 thermistor, an intelligent module 103 adopts AI-708 intelligent module.

Wherein, when the nonlinear crystal is not subjected to laser frequency conversion and laser frequency conversion is performed, in order to maintain the nonlinear crystal 101 at the set operating temperature _T1 , the temperature control power supply 104 needs to output different heating to the temperature control furnace 105. Voltage. The oscilloscope 106 respectively measures the waveforms W ₁ and W ₂ of the heating voltage output from the temperature control power supply 104 to the temperature control furnace 105 when the laser frequency conversion is not performed and when the laser frequency conversion is performed, so that the heating electric power P generated by the temperature control furnace 105 can be calculated ₁ and _P2 . Since the nonlinear crystal 101 absorbs the laser light in the process of laser frequency conversion, it will generate a certain thermal power, so there is a difference between the heating electric power P ₁ and P ₂ generated by the temperature control furnace 105, and the difference value (P ₁ -P ₂ ) is the thermal power generated by the nonlinear crystal 101 absorbing laser light during laser frequency conversion.

When the nonlinear crystal 101 is not subjected to laser frequency conversion, in order to maintain the nonlinear crystal 101 at the set operating temperature _T1 , the temperature control power supply 104 needs to output a certain heating voltage to the temperature control furnace 105, and the oscilloscope 106 records the next paragraph The heating voltage waveform W ₁ output by the temperature control power supply 104 to the temperature control furnace 105 within the time t can be calculated according to the heating voltage waveform W ₁ , the effective heating voltage value of 24V and the resistance value of the heating wire inside the temperature control furnace 105 of 34Ω. The heating electric power generated by 105 is P ₁ , and its calculation formula is:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; R</span>}}<span\; class="notranslate">\; \&times;</span>\frac{{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; t</span>}}$

Among them, U is the effective value of the heating voltage, R is the resistance value of the heating wire, t ₀ is the working time of the temperature control power supply 104, and t is the total measurement time (t ₀ and t can be obtained from the heating voltage waveform W ₁ ). When the nonlinear crystal 101 performs laser frequency conversion, in order to maintain the nonlinear crystal 101 at the set operating temperature _T1 , the temperature control power supply 104 needs to output different heating voltages to the temperature control furnace 105, and the oscilloscope 106 records In this case, the voltage waveform W ₂ output from the temperature control power supply 104 to the temperature control furnace 105 within a period of time t is also based on the heating voltage waveform W ₂ , the effective value of the heating voltage 24V and the resistance value of the heating resistance wire inside the temperature control furnace 105 34Ω The heating electric power P ₂ generated by the temperature control furnace 105 can be calculated. Since the nonlinear crystal 101 absorbs the laser light in the process of laser frequency conversion, it will generate a certain thermal power, so there is a difference between the heating electric power P ₁ and P ₂ generated by the temperature control furnace 105, and the difference value (P ₁ -P ₂ ) is the thermal power generated by the nonlinear crystal 101 absorbing laser light during laser frequency conversion.

Regardless of the wavelength of the laser light absorbed by the nonlinear crystal 101 during the laser frequency conversion process, or the absorption coefficient of the nonlinear crystal 101 for the laser, or the nonlinear crystal 101 absorbs the fundamental frequency light or the frequency conversion light, this method Both can conveniently measure the thermal power generated by the nonlinear crystal absorbing laser light.

Example:

The purpose, features and advantages of the present invention are further illustrated by the accompanying drawings and examples, but the present invention is not limited to these examples.

In this embodiment, the device for measuring the thermal power generated by the nonlinear crystal absorbing laser light provided by the present invention is used to measure the thermal power generated by the nonlinear crystal PPMgLN absorbing laser light in the PPMgLN-OPO experiment. Please refer to Figure 2, Figure 3, Figure 4 and Figure 5.

In Fig. 2, 201 is a nonlinear crystal, 202 is a temperature sensor, 203 is an intelligent module, 204 is a temperature control power supply, 205 is a temperature control furnace, 206 is an oscilloscope, 207 is a 1064nm pulse pumping light source, 208 is a laser light path, 209 is an optical isolator, 210 is a converging lens, 211 is an OPO input mirror, 212 is an OPO output mirror, 213 is a 45° filter, 214 is a power meter, and 215 is a trash can.

A temperature sensor 202 , an intelligent module 203 , a temperature control power supply 204 and a temperature control furnace 205 constitute a temperature control system 002 . The temperature control system 002 controls the working temperature of the nonlinear crystal 201 , and the oscilloscope 206 measures the heating voltage output from the temperature control power supply 204 in the temperature control system 002 to the temperature control furnace 205 . The effective value of the heating voltage output by the temperature control power supply 204 to the temperature control furnace 205 is 24V. The temperature control furnace 205 uses a constantan wire with a resistance value of 34Ω as the heating wire, the temperature sensor 202 is a Pt100 thermistor, and the intelligent module 203 uses AI-708 intelligent module.

1064nm pulse pumping light source 207, optical isolator 209, converging lens 210, OPO input mirror 211, nonlinear crystal 201, OPO output mirror 212, 45° filter 213 and power meter 214 are sequentially placed on the same optical path. The 1064nm pulsed pumping light source 207 outputs near-fundamental mode light beams, with a pulse repetition frequency of 10kHz, a pulse width of 60ns, and a maximum output power of 22W. The laser light output by the 1064nm pulsed pumping light source 207 is focused on the center of the nonlinear crystal 201 after passing through the converging lens 210, and the focusing diameter is 0.6mm. The nonlinear crystal 201 is a PPMgLN crystal with a size of 30×12×2mm ³ and a polarization period of 29.35 μm. Both ends are coated with high transmittance films for signal light, idler light and pump light (R<1% 1.3-- 1.5 μm, R<1.5% 3.6--4.7 μm, R<2% 1.064 μm), the crystal works at the set temperature T ₁ =80°C. The OPO input mirror 211 is a plane mirror, the material is quartz, and the surface is coated with a film with high transmittance for pump light and high reflectivity for signal light and idler light (T=99.0% 1.064 μm, R>99.9% 1.3--1.5 μm, R>99.0%3.6--4.7μm); OPO output mirror 212 is a plane mirror, the material is CaF ₂ , the surface is coated with a high reflectivity film for pump light and signal light, and a high transmittance film for idler light (R=98.0%1.064 μm, R>99.5% 1.3--1.5 μm, T>98.0% 3.6--4.7 μm). The spatial distance between the OPO input mirror 211 and the OPO output mirror 212 is 65 mm, forming a resonant cavity for single resonance of the signal light. The surface of the 45° filter 213 is coated with a high reflectivity film for pump light and signal light, and a high transmittance film for idler light (R=98.0% 1.064 μm, R>99.5% 1.3--1.5 μm, T>98.0% 3.6- -4.7 μm, 45° incident condition). The power meter 214 measures the power of the idler light passing through the 45° filter 213 , and the dustbin 215 receives the pump light and the signal light reflected by the 45° filter 213 .

During the experiment, the temperature T ₁ set by the nonlinear crystal 201 was always kept at 80°C. When the nonlinear crystal 201 does not carry out laser frequency conversion, that is, when the laser power output by the 1064nm pulsed pumping light source 207 is 0W, use the oscilloscope 206 to record the heating voltage waveform W ₁ (recording time 50s), the recording result is shown in Figure 3. From the data of the waveform W ₁ , the effective heating voltage value of 24V and the resistance value of the heating wire in the temperature control furnace 205 of 34Ω, it can be calculated that the heating electric power P ₁ generated by the temperature control furnace 205 is 1.5W. When the laser power output by the 1064nm pulsed pumping light source 207 is a maximum value of 22W, the power meter 214 measures that the idler frequency light power is 3.4W. Also use the oscilloscope 206 to record the heating voltage waveform W ₂ output from the temperature control power supply 204 to the temperature control furnace 205 (recording time is 50s), and the recording result is shown in FIG. 4 . It can be seen that there is a clear difference between the heating voltage waveforms _W2 and _W1 . Similarly, it can be calculated that the heating electric power P ₂ generated by the temperature control furnace 205 is 6.3W. Therefore, when the nonlinear crystal 201 is pumped by a 22W pulsed laser, the thermal power generated by absorbing laser light is (P ₁ -P ₂ )=6.3W−1.5W=4.8W. Using the same method, the thermal power generated by the nonlinear crystal 201 absorbing laser light under different pump power conditions can be measured, and the measurement results are shown in FIG. 5 .

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (6)

1. A device for measuring the thermal power of a nonlinear crystal, characterized in that the device comprises a nonlinear crystal (101), a temperature sensor (102), an intelligent module (103), a temperature control power supply (104), a temperature control furnace (105) and oscilloscope (106), wherein: The nonlinear crystal (101) is placed inside the temperature control furnace (105), works at a certain set temperature _T1 , and plays the role of laser frequency conversion; A temperature sensor (102), used to measure the actual working temperature T0 of the nonlinear crystal (101), and feed back this value to the intelligent module (103); The intelligent module (103) is used to compare the actual working temperature _T0 of the nonlinear crystal (101) measured by the temperature sensor (102) with the set temperature _T1 , and accordingly adjust the temperature control power supply (104) to the temperature control The heating voltage output by the furnace (105) controls the nonlinear crystal (101) at the set working temperature _T1 ; Temperature control furnace (105), adopts heating wire as heating element; A temperature sensor (102), an intelligent module (103), a temperature control power supply (104) and a temperature control furnace (105) constitute a temperature control system (001), and an oscilloscope (106) measures in real time the temperature control power supply (104) to the temperature control furnace ( 105) Waveform W of the output heating voltage. 2. The device for measuring the size of nonlinear crystal thermal power according to claim 1, characterized in that, When the nonlinear crystal (101) is not subjected to laser frequency conversion, in order to maintain the nonlinear crystal (101) at the set operating temperature _T1 , the temperature control power supply (104) needs to supply the temperature control furnace (105) Output a certain heating voltage, the oscilloscope (106) records the heating voltage waveform W ₁ output by the temperature control power supply (104) to the temperature control furnace (105) in a period of time t, according to the heating voltage waveform W ₁ and the temperature control furnace (105) The resistance value of the internal heating resistance wire can calculate the heating electric power size P ₁ that the temperature control furnace (105) produces; When the nonlinear crystal (101) is performing laser frequency conversion, in order to still maintain the nonlinear crystal (101) at the set operating temperature _T1 , the temperature control power supply (104) needs to supply the temperature control furnace (105) Output different heating voltages, and the oscilloscope (106) records the voltage waveform W ₂ output from the temperature control power supply (104) to the temperature control furnace (105) in a period of time t in this case, according to the voltage waveform W ₂ and the temperature control furnace ( 105) Calculate the heating electric power P ₂ generated by the temperature control furnace (105) from the resistance value of the internal heating resistance wire. 3. The device for measuring the nonlinear crystal thermal power size according to claim 2, characterized in that there is a difference between the heating electric power size _P1 and _P2 that the temperature control furnace (105) produces, and this difference value P ₁ -P ₂ is the magnitude of thermal power generated by the nonlinear crystal (101) due to absorption of laser light during laser frequency conversion. 4. The device for measuring the thermal power of a nonlinear crystal according to claim 1, characterized in that, the nonlinear crystal (101) comprises a PPLN, PPKTP, PPLT, KTP, LBO or BBO crystal. 5 . The device for measuring the thermal power of a nonlinear crystal according to claim 1 , wherein the laser frequency conversion process performed by the nonlinear crystal ( 101 ) includes optical parametric oscillation, frequency doubling and sum frequency. 6. The device for measuring the thermal power of a nonlinear crystal according to claim 1, characterized in that, the laser light absorbed by the nonlinear crystal (101) during laser frequency conversion is fundamental frequency light or frequency conversion light.

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