CN101087056A - Dual vertical mode stable frequency laser - Google Patents

Abstract

The invention is double-model frequency stabilized laser which is relative with two lasers which are used in output of single frequency laser interferometer, it can resolve problem that P and S polarization output by laser can not be separated fully, loss of output power is big, polarization state of output module is not stable. The tube wall of double-model laser (1) is connected with heater (2); the output is connected with input of amplifier A0 via LCD modulator (3), polarizing film (4), photoelectricity receiver (5) and amplifier A0, output of the amplifier A0 is connected with input of multiple-way switch (6), oscillator (7) is connected with input of LCD modulator (3) and control end of multiple-way switch (6), two outputs of the multiple-way switch (6) are separately connected with input of subtracter A3 via voltage keeper (8) constructed by resistance R and capacitance C, output of subtracter A3 and timer (11) is connected with input of analogue switch (9), output of analogue switch (9) is connected with heater (2) via power amplifier (10), tube wall of double-model laser (1) possesses transverse stress infliction device.

Description

Dual vertical mode stable frequency laser

Technical field:

The present invention is relevant with the laser that has two longitudinal modes to export simultaneously.

Background technology:

Indication dual vertical mode stable frequency laser of the present invention is the light source of single frequency laser interferometer.

Frequency stabilized carbon dioxide laser refers to that the optical maser wavelength of output has certain precision by the laser of frequency stabilization system control, to guarantee the measurement accuracy of laser interferometer.According to the standing-wave condition of laser resonant cavity, the essence of frequency stabilization system is that the resonant cavity of stable laser is long.Dual vertical mode stable frequency is a kind of method of laser frequency stabilization, is applicable to the He-Ne laser of two longitudinal mode outputs.

The longitudinal mode spacing Δ f of laser output and the pass of cavity length L are:

$\mathrm{\&Delta;f}=\frac{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="A20071004939600081.png,A20071004939600111.png"\; state="\{\{state\}\}">C</figure-callout>}}{2\mathrm{nL}}$

C is the light velocity, and n is the refractive index in the resonant cavity, and when the long L increase in chamber, longitudinal mode spacing Δ f reduces, when its during less than doppler bandwidth 1500MHz, then laser has two or more longitudinal modes to export simultaneously.Can calculate, when laser chamber length was 150mm, longitudinal mode spacing was about 1080MHz, and laser keeps two longitudinal modes outputs, as shown in Figure 1.Mode competition makes two adjacent moulds be orthogonal polarization state (P and S), and corresponding output frequency is f1 and f2, and the condition of utilizing two polarization mode amplitudes to equate usually realizes frequency stabilization, and existing dual vertical mode stable frequency laser as shown in Figure 2.

Beat according to oscillator 7, P and S polarization mode arrive subtracter A3 at height (" 1 ") low (" the 0 ") level of oscillator signal through liquid crystal modulator 3, polarizer 4, photelectric receiver 5, amplifier A0, variable connector 6, voltage retainer 8 respectively, when the amplitude of P polarization mode and S polarization mode does not wait, the deviation value of subtracter A3 output drives heater 2 through analog switch 9, power amplifier 10, utilize expansion principle control double-longitudinal-mode laser 1, it is long to make it to remain on the resonant cavity that two moulds outputs equate, reaches the frequency stabilization purpose.Timer 11 is in order to control the time that is opened to system's closed loop from laser, and its cycle can be set with the time, also can determine according to the temperature or the mode hopping frequency of laser.

Matching relationship between the output of double-longitudinal-mode laser 1, liquid crystal modulator 3 and the polarizer 4 as shown in Figure 3 and Figure 4, Fig. 3 is the position relation between output, liquid crystal modulator 3 and polarizer 4 optical axises of double-longitudinal-mode laser 1, and Fig. 4 be the output situation under oscillator 7 acts on.

When dual vertical mode stable frequency laser is used for single frequency laser interferometer, utilize polarizer to suppress an output mould usually, and not repressed mould is as the light source of instrument.

There are three problems in above-mentioned dual vertical mode stable frequency laser: 1. in the double-longitudinal-mode laser, because mode competition has guaranteed that two moulds of output are orthogonal polarised light (P, S), but because the isotropic characteristics of laser, the initial angle α of polarization direction has randomness when each time opened, as shown in Figure 5.This randomness makes that P can not separate fully with the S polarization mode in the process of " liquid crystal modulator-polarizer-photoelectricity receive ", causes laser interferometer to produce noise even can not work; 2. there are two kinds of random polarization states in frequency stabilization output, and as shown in Figure 6 and Figure 7, the P polarization mode is in the low-frequency range of gain curve among Fig. 6, and respective frequencies is f1, and the P polarization mode is in the high band of gain curve among Fig. 7, and respective frequencies is f2.If suppress the S polarization mode with polarizer, allow f1 output at Fig. 6, and allow f2 output among Fig. 7, in laser interferometer, this is unallowed; 3. owing to adopt P and two amplitude frequency stabilizations such as mould of S, suppress a mould with polarizer, the power output loss of laser is 50%.

Summary of the invention:

The purpose of this invention is to provide a kind of P and can separate fully with the S polarization mode, power output is big, the constant dual vertical mode stable frequency laser of polarization state of each closed loop output mould.

The present invention is achieved in that

Dual vertical mode stable frequency laser of the present invention, the tube wall of double-longitudinal-mode laser 1 is connected with heater 2, its output is connected with the input of amplifier A0 through liquid crystal modulator 3, polarizer 4, photelectric receiver 5, the output of amplifier A0 connects the input of variable connector 6, oscillator 7 connects the control end of liquid crystal modulator 3 and variable connector 6, and the output of the two-way of variable connector 6 meets subtracter A through separately the voltage retainer 8 that is made of resistance R and capacitor C respectively ₃Input, subtracter A ₃Connect the input of analog switch 9 with the output of timer 11, the output of analog switch 9 connects heater 2 through power amplifier 10, on double-longitudinal-mode laser 1 tube wall lateral stress bringing device is arranged.

The lateral stress bringing device is by two bearing G of tube wall ₁, G ₂And two the application of force bolt that contacts with tube wall between the bearing form.

The two-way output of variable connector 6 is respectively through the first amplifier A ₁, the second amplifier A ₂Be connected with voltage retainer 8, first and second amplifier has first and second feedback resistance R respectively ₁, R ₂, the first feedback resistance R ₁≠ the second feedback resistance R ₂

The first amplifier A ₂Output meet voltage comparator A ₄Negative sense input, voltage comparator A ₄Forward input meet comparative level V0, voltage comparator A ₄Connect two inputs of NAND gate 12 with the output of timer 11, the output of NAND gate 12 connects the set terminal of rest-set flip-flop 13, and the output of rest-set flip-flop 13 connects the control end of analog switch 9.

The present invention adopts and applies prestressed method assurance laser has fixed-direction when each unlatching the P, S polarization state, and P can be separated fully with the S polarization mode, has guaranteed the functional reliability of laser interferometer, has avoided generating noise.Adopt asymmetric frequency stabilization circuit, guarantee that a mould has bigger power output, reduces the power output loss of laser.Adopted the polarization judging circuit that constitutes by voltage comparator A4, NAND gate 12 and rest-set flip-flop 13, guaranteed that the polarization state of each closed loop output mould is constant, made laser interferometer energy steady operation.

The present invention is simple in structure, and is with low cost, and reliable operation can guarantee the normal steady operation of instrument as the light source of single frequency laser interferometer.

Description of drawings:

Fig. 1 is the output mould of double-longitudinal-mode laser.

Fig. 2 is the circuit theory diagrams of existing dual vertical mode stable frequency laser.

Fig. 3 is laser, liquid crystal modulator and the correct match map of polarizer optical axis.

Fig. 4 is the modulation output map of double longitudinal mode laser.

Fig. 5 is a double-longitudinal-mode laser output polarization randomness schematic diagram.

Fig. 6 is a kind of output state of existing dual vertical mode stable frequency laser.

Fig. 7 is the another kind of output state of existing dual vertical mode stable frequency laser.

Fig. 8 is circuit theory diagrams of the present invention.

A kind of output state of the asymmetric frequency stabilization of Fig. 9.

The another kind of output state of the asymmetric frequency stabilization of Figure 10.

Embodiment:

The present invention is applicable to that the chamber is long for two longitudinal mode He-Ne lasers of 150mm, and is in service at laser, keeps two longitudinal modes to export simultaneously.

The double longitudinal mode laser frequency stabilized carbon dioxide laser that the present invention proposes as shown in Figure 8.

Under bearing G1, G2 and application of force bolt F effect, the housing of double-longitudinal-mode laser 1 is in deformation state.The square wave drive liquid crystal modulator 3 that oscillator 7 produces, make it P, the S polarization mode of double-longitudinal-mode laser 1 output be replaced half-twist according to fixing beat, and be input to amplifier A1 and A2 respectively through polarizer 4, photelectric receiver 5, amplifier A0 and variable connector 6 successively, the output of amplifier A1 and A2 is remembered by RC voltage hold circuit 8 separately, and obtain difference at subtracter A3, drive heater 2 through analog switch 9, power amplifier 10, the chamber of control double-longitudinal-mode laser 1 is long.Timer 11 is in order to be provided with the initial time that is opened to system's closed loop from laser, voltage comparator A4 is used to judge the amplitude of polarization mode, when timer 11 and voltage comparator A4 satisfy condition output level when jumping to high voltage " 1 " by low level " 0 ", NAND gate 12 output redirects are low level " 0 ", drive rest-set flip-flop 13 upsets, 9 conductings of control analog switch, system's closed loop reaches the frequency stabilization purpose.

Main points of the present invention are:

1, employing applies prestressed method and guarantees that laser has P, the S polarization state of fixed-direction when each start.

Shown in wire frame fig1 among Fig. 7, two bearing G1, G2 and application of force bolt F act on the tube wall of double-longitudinal-mode laser 1, double-longitudinal-mode laser 1 produces anisotropy because of little distortion under external force, is maintained fixed relation thereby make its output polarization and apply force direction.

2, adopt asymmetric frequency stabilization circuit, guarantee that a mould has bigger power output.

In the wire frame fig2 of Fig. 7, suppose the corresponding S polarization mode of amplifier A1, the corresponding P polarization mode of amplifier A2, the multiplication factor of two amplifiers is respectively:

β _s＝R1/R3

β _p＝R2/R3

Adjust resistance R 1 or R2, make β _s≠ β _p, frequency stabilization circuit is closed loop under asymmetrical state, makes the top of the close laser gain curve of output mould that corresponding multiplication factor is little in the double-longitudinal-mode laser.β for example _p＜β _s, then to export as shown in figure 10, P polarization mode output amplitude is bigger.In actual use, with polarizer filtering S polarization mode, keep the P polarization mode.With respect to the equal strength frequency stabilization system, obtained bigger power output.

3, designed the polarization judging circuit, shown in wire frame fig3 among Fig. 8, guaranteed that the polarization state of the each closed loop output of dual vertical mode stable frequency laser mould is constant.

As described above, if β _p＜β _s, guaranteed that P polarization mode output amplitude is bigger, still there are two kinds of possible polarization states this moment, as Fig. 9 and Figure 10,, designed the polarization judging circuit for guaranteeing the polarization uniqueness of output, A4 is a voltage comparator, and its reverse input end connects the output of P polarization mode amplifier A2.Figure 10 represents the establishing method of comparative level V0 (positive input of A4), the P polarization mode moves in laser output gain curve from left to right in laser unlatching warm, corresponding amplifier A2 is output as V0 when moving to G0, the output of voltage comparator A4 by low level to high level upset (" 0 " → " 1 "), if this moment, timer 11 also was in completion status (" 1 "), then NAND gate 12 outputs are by " 1 " change " 0 ", rest-set flip-flop 13 upset output level"1"s, analog switch 9 conductings, system is closed loop immediately, guaranteed the output polarization state as shown in figure 10 of frequency stabilization system, the P polarization mode is constant in the f1 position.

Claims (4)

1, dual vertical mode stable frequency laser, the tube wall that it is characterized in that double-longitudinal-mode laser (1) is connected with heater (2), its output is connected with the input of amplifier AO through liquid crystal modulator (3), polarizer (4), photelectric receiver (5), the output of amplifier AO connects the input of variable connector (6), oscillator (7) connects the control end of liquid crystal modulator (3) and variable connector (6), and the output of the two-way of variable connector (6) meets subtracter A through separately the voltage retainer (8) that is made of resistance R and capacitor C respectively ₃Input, subtracter A ₃And the output of timer (11) connects the input of analog switch (9), and the output of analog switch (9) connects heater (2) through power amplifier (10), on double-longitudinal-mode laser (1) tube wall lateral stress bringing device is arranged.

2, dual vertical mode stable frequency laser according to claim 1 is characterized in that two the bearing Gs of lateral stress bringing device by tube wall ₁, G ₂And two the application of force bolt that contacts with tube wall between the bearing form.

3, dual vertical mode stable frequency laser according to claim 1, the two-way output that it is characterized in that variable connector (6) is respectively through the first amplifier A ₁, the second amplifier A ₂Be connected with voltage retainer (8), first and second amplifier has first and second feedback resistance R respectively ₁, R ₂, the first feedback resistance R ₁≠ the second feedback resistance R ₂

4, dual vertical mode stable frequency laser according to claim 1 is characterized in that the first amplifier A ₂Output meet voltage comparator A ₄Negative sense input, voltage comparator A ₄Forward input meet comparative level VO, voltage comparator A ₄And the output of timer (11) connects two inputs of NAND gate (12), the set terminal of the output connection rest-set flip-flop (13) of NAND gate (12), the control end of the output connection analog switch (9) of rest-set flip-flop (13).

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