JPH02130982A - Laser oscillator - Google Patents

Abstract

PURPOSE:To manufacture an oscillator in high laser oscillation efficiency at low cost by a method wherein a transmission type crystal cell as a Q switch is arranged between a laser medium and a reflector making a brewster angle. CONSTITUTION:A flat plated transmission type liquid crystal cell 4 tilted by brewster angle thetaB is arranged on the optical axis between a laser medium 1 and an output side reflector 3. When the medium 1 is continuously excited by a lamp 8, even if laser beams enter from the medium 1 to the cell 4 in the off state of a liquid crystal cell driver 6 not impressing the cell 4 with any voltage conforming to the control signals from a control circuit 9, both of the P, S polarization components of laser beams transmitting the cell 4 amounting to 85% are attenuated by the reciprocation between the reflectors 2 and 3 to interrupt the laser oscillation for augmenting the energy stored in the medium 1. In such a state, when the energy is stored in the medium 1 while the cell 4 is abruptly turned on, the stored energy is discharged at once. Through these procedures, the title oscillator in high laser oscillation efficiency and excellent maintenability can be manufactured at low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser oscillator, and particularly to a laser oscillator suitable for improving laser oscillation efficiency and reducing costs when obtaining a pulsed laser.

[Conventional technology]

While the laser medium is being pumped, the loss in the resonator is increased to suppress laser oscillation, and then the loss in the resonator is suddenly reduced to increase the Q to favor laser oscillation, which increases the power. Very high-power laser light is emitted in a pulsed manner. Conventionally, Q-switches that change the Q value in a switch-like manner generally use elements that utilize an acousto-optic effect (AO element), elements that utilize electro-optic effect (EO element), or saturated dyes. elements are used.

In addition, as related to the conventional Q switch, Ohmsha's "Optical Terminology Dictionary" edited by Takashi Hioki (published in 1981), No. 5
5 pages, Ohmsha's ``Laser Handbook J Laser Society IIX'' (published in 1981), etc.

[Problem to be solved by the invention]

In the above conventional technology, an acousto-optic effect element (AO element)
However, there is a problem in that the method can only cope with pulsing of a continuous wave laser with a low laser gain, and requires an expensive high frequency driver of 20 to 50 MHz. Although electro-optic effect elements (EO elements) have excellent performance, they require a linear polarizing element and a driver that switches a high voltage of 5 to 10 kV at high speed, resulting in an increase in cost.

Further, devices using saturated dyes have the problem that one dye deteriorates quickly and maintenance is not easy.

An object of the present invention is to provide a laser oscillator equipped with a Q switch that is inexpensive, has excellent maintainability, and has high laser oscillation efficiency.

[Means to solve the problem]

The above purpose uses a transmission type liquid crystal cell as a Q switch,
This is achieved by arranging the laser medium and the reflector at an angle of Brewster's angle.

Note that it is not necessary to incline exactly by Brewster's angle, and the reflectance of linearly polarized light by the surface is 0.2 for the P polarized light component.
% or less, and by tilting the S-polarized light component by an angle of 11% or more, the above object can be achieved.

When driving a Q-switch made of a transmissive liquid crystal cell, the transmissive liquid crystal cell is turned on while the laser medium is excited.
A driving voltage is applied between the transparent electrodes to change the state from FF to ON. In this case, it is preferable to change the OFF state to the ON state when the intensity of the S-polarized component of the reflected light on the surface of the transmissive liquid crystal cell reaches a required value.

In addition, the thickness of the transparent electrode of the transmissive liquid crystal cell should be 800 Å or less, and the glass substrate of the transmissive liquid crystal cell should be made of a low alkaline material, and the laser emission side surface of the transmissive liquid crystal cell should have the required reflectance. It is preferable to apply a coating film.

[Effect]

A transmissive liquid crystal cell is used as a Q switch, and the transmissive liquid crystal cell is turned off while the laser medium is pumping.
This state is set to prevent round-trip reflection of laser light inside the resonator, and when a laser pulse is generated, it is turned on to allow round-trip reflection of laser light by both mirrors. As a result, the energy stored in the laser medium is emitted as laser light. This laser pulse oscillator uses an inexpensive transmission type liquid crystal cell and does not require an expensive driver, so manufacturing costs are reduced. Additionally, since the transmissive liquid crystal cell is arranged at the required angle, the linear polarizing element used in the past is no longer required.

Costs are also reduced accordingly.

If the Q switch is turned ON when the intensity of the S-polarized component reflected light on the surface of the transmissive liquid crystal cell reaches a certain level, a high-power pulsed laser can be obtained.

In addition, reducing the thickness of the transparent electrode of a transmissive liquid crystal cell to 800 Å or less reduces loss, and making the glass substrate low alkaline eliminates the need for a silicon oxide base film, which is normally provided, and also provides a high reflectance coating. When a membrane is provided,
The coating film serves as a reflecting mirror, and one of the reflecting mirrors becomes unnecessary.

〔Example〕

A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a laser oscillator according to an embodiment of the present invention. In this embodiment, a perfect reflecting mirror 2 and an output side reflecting mirror 3 are arranged opposite to each other with the laser medium 1 in between, and the laser medium 1
A flat transmissive liquid crystal cell 4 is arranged on the optical axis 5 between the output side reflecting mirror 3 and the output side reflecting mirror 3. This transmission type liquid crystal cell 4 is
It is inclined with respect to the optical axis 5 by a Brewster angle θB.

A lamp 8 is juxtaposed to the laser medium 1 , and the lamp 8 is supplied with power from the excitation power source 7 to supply optical energy to the laser medium 1 . Further, transparent electrodes 16a and 16b (FIG. 2) of the transmissive liquid crystal cell 4 are connected to a liquid crystal cell driver 6.

Both the liquid crystal cell driver 6 and the excitation power source 7 are connected to a control circuit 9, and are used to supply optical energy to the laser medium 1 and to change the transmissive liquid crystal cell 4 from the OFF state (light blocking state) to the ON state (light passing state). ) is controlled.

FIG. 2 is a cross-sectional view of the transmission type liquid crystal cell 4. FIG.

The transmission type liquid crystal cell 4 of this embodiment has a flat transparent electrode 16 disposed inside between two opposing glass substrates 15a and 15b.
A and 16b are attached and formed to face each other, and alignment films 18a and 18b for aligning the liquid crystal are attached and formed to face each other on the inside thereof, and a liquid crystal 17 is interposed between the alignment films L8a and 18b. As the liquid crystal 17, nematic liquid crystal, ferroelectric liquid crystal, or the like is used.

1 quartz glass is used as the glass substrates 15a and 15b.

In this embodiment, a glass having a low alkali content and good laser transmittance, such as borosilicate crown glass or Corning's 7059 type, is used. If you use glass with low alkaline content like this.

A silicon oxide base film to prevent alkaline components from leaching out (this film contributes to laser loss) is no longer required.

FIG. 3 is a graph showing the correlation between the film thickness of the transparent electrodes 16a and 16b and the loss of laser light. According to this graph, it can be seen that when the number of transparent electrodes 16a and 16b exceeds 800, the laser loss increases.

Therefore, in this embodiment, the thickness of the transparent electrodes 16a and 16b is set to 800 Å or less.

Next, the reason why the transmissive liquid crystal cell 4 is tilted at a Brewster angle θB with respect to the optical axis 5 will be described.

Assuming that the refractive index of the glass substrates 15a and 15b forming the outermost part of the transmissive liquid crystal cell 4 is 1.5, the relationship between the angle of incidence θ on the glass surface and the reflectance R or transmittance T is as follows. It is known that the situation shown in Figure 4 will occur (for example,
``Optics'' by Kazumi Murata, published by Science Publishing! Fr158
In this case, the incident angle θ is determined by tanθB = 1.5 (refractive index of glass), which is the Brewster angle θB.
, a part of the S-polarized component of the incident light is reflected by the surface of the transmissive liquid crystal cell 4, but the P-polarized component is not reflected and becomes 1
The state becomes 00% transparent.

Next, the operation of the laser oscillator shown in FIG. 1 in a state where the laser medium 1 is continuously excited by the lamp 8 will be described.

In response to a control signal from the control circuit 9, the lamp 8 supplies optical energy to the laser medium 1, and the liquid crystal cell driver 6 is in a state in which no voltage is applied to the transmissive liquid crystal cell 4 (the transmissive liquid crystal cell 4 is in the OFF state). In this case, the laser light emitted from the laser medium 1 has not reached a steady state and enters the transmission type liquid crystal cell 4 as elliptically polarized light. On the incident side surface of the transmissive liquid crystal cell 4, 100% of the P-polarized light component is transmitted, and about 15% of the S-polarized light component is reflected (reflected light Rs in FIG. 1), and about 85% of the S-polarized light component is transmitted. Each polarized light component that passes through the liquid crystal layer 17
Rotate 0 degrees. Therefore, when injecting the liquid crystal layer 17,
The P polarization component is 85% and the S polarization component is 100%. Of the polarized light components that have passed through the liquid crystal layer 17, the S polarized light component is further reflected by approximately 15% on the glass surface on the exit side. Both polarization components are 85%.

In other words, each time it passes through the transmission type liquid crystal cell 4, the intensity increases by 8
It will be 5%, so it will take 10 round trips between two and three mirrors.

(0,85)"; 0.04, and the intensity of the laser beam decreases to 4%. In other words, even when the laser medium 1 is continuously excited by the lamp 8, the transmissive liquid crystal cell 4 is turned off. In this state, laser oscillation is sufficiently inhibited.The energy stored in the laser medium 1 is therefore increased.

In a state where the stored energy of the laser medium 1 is high, the liquid crystal cell driver 6 operates the transparent electrode 16a of the transmissive liquid crystal cell 4,
When a potential is applied between 16b and the liquid crystal layer 17 is aligned (
ON state). In this ON state, the laser beam is
The polarization direction is not U-turned in the liquid crystal layer 17. Therefore, 100% of the P-polarized light component is transmitted through the transmission type liquid crystal cell 4. On the other hand, the intensity of the S-polarized component decreases to 72% with each pass. In other words, when the two reflecting mirrors 2 and 3 make 10 round trips, the P polarized light component does not decrease, but the S polarized light component becomes (0,72)''# 0.001 and decreases to 0.1%, that is, P Only the polarizing acid remains.

Therefore, if the transmissive liquid crystal cell 4 is turned OFF to accumulate energy in the laser medium 1, and when the accumulated energy increases, the transmissive liquid crystal cell 4 is suddenly turned ON to cancel the laser oscillation blocking factor. The energy is emitted all at once, and a short pulse laser with a high peak value is emitted.

Next, the operation of the laser oscillator when the lamp 8 is lit in pulses to excite the laser medium 1 in pulses will be explained with reference to FIG.

When pulsed power is supplied from the excitation power source 7 to the lamp 8 in response to a control signal from the control circuit 9, the lamp 8 emits light energy having time characteristics as shown in the top row of FIG. 5 to the laser medium 1. is irradiated.

The laser medium 1 that has received this irradiation energy is 2 in FIG.
Energy is stored internally with the time characteristics shown in the row.

At a time tI&d when this stored energy reaches its maximum, the control circuit 9 sends a control signal to the liquid crystal cell driver 6, and the fifth
The voltage shown in the figure is the transparency f! of the transmissive liquid crystal cell 4! ! Control the voltage to be applied to the pole. The applied voltage at this time is preferably a rectangular pulse that does not contain a DC component, and in this example,
Peak value is 5~30V, pulse repetition frequency is 1~L
It is a rectangular pulse signal of OkHz. When this voltage is applied to the transmissive liquid crystal cell 4, 1. At time t2 with a certain time delay, the transmission type liquid crystal cell 4 is turned on, and the energy stored in the laser medium 1 is emitted all at once as optical energy.

Next, in the above-described embodiment, a time t after a certain time delay from the time t1 at which the stored energy of the laser medium 1 becomes maximum.
2, a preferred embodiment for controlling the timing of turning on the transmissive liquid crystal cell 4 will be described with reference to FIG. 6.
In this embodiment, the photoelectric conversion element 12 is placed at a position that receives the S-polarized component of the laser beam reflected by the transmissive liquid crystal cell 4.

As described above, about 15% of the S-polarized light component is reflected on the glass surface of the transmissive liquid crystal cell 4. The intensity of this S-polarized component is
9 has a correlation with the energy stored in the laser medium 1. Therefore, the detection signal of the photoelectric conversion element 12 causes the S
By setting the time t1 to be the time when the polarization component intensity exceeds the required value, optimal timing control becomes possible.

FIG. 7 is an explanatory diagram of main parts according to another embodiment of the present invention. The transmissive liquid crystal cell 13 used in this embodiment has a high reflectance coating [ 14 is provided. This coating film 14
It reflects the laser beam in place of the output-side reflecting mirror 3 shown in the figure, and in this embodiment there is no need to provide a separate output-side reflecting mirror, so the device can be made more compact.

In each of the embodiments described above, the transmissive liquid crystal cell 4 is tilted at an optimum angle of Brewster's angle with respect to the optical axis.
The present invention does not require precise Brewster angle tilting to achieve its objectives.

In other words, when the transmissive liquid crystal cell is in the ON state, the laser light that has not reached the steady state layer goes back and forth inside the resonator, so that the P-polarized light component becomes 90% or more and the S-polarized light component becomes 1% or less. It is sufficient if it can be separated into Based on this value, the reflectance of each polarized light component per time by the outermost material of the transmissive liquid crystal cell (glass was used in each of the above examples) is calculated to be 0.2% for the P polarized light component. Below, the S polarization component is 11%
It can be seen that it is sufficient to tilt the transmission type liquid crystal cell with respect to the optical axis at the above angle. When glass is used as the outermost part of a transmission type liquid crystal cell, its refractive index varies from about 1.45 to 1.5, but when glass with a refractive index of 1.5 is used, the characteristic diagram shown in Figure 4 Therefore, if the optical axis is tilted within a range of 50 degrees to 60 degrees, the same effects as those of the embodiments of the present invention described above can be obtained.

In each of the above-mentioned embodiments, if there is a concern that the temperature of the transmissive liquid crystal cell will rise due to the laser beam reflected back and forth inside the resonator, a cooling means for cooling the transmissive liquid crystal cell with air, water, or oil may be provided. That's fine.

〔Effect of the invention〕

According to the present invention, an inexpensive transmission type liquid crystal cell is used as a Q-switch and is arranged at a required angle of inclination, thereby eliminating the need for a linear polarizing element, so that manufacturing costs can be reduced. Furthermore, since laser loss inside the resonator is small, laser oscillation efficiency can be improved.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a laser oscillator according to a first embodiment of the present invention, FIG. 2 is a cross-sectional view of the transmission type liquid crystal cell shown in FIG. 1, and FIG. 3 is a film thickness of the transparent electrode of the transmission type liquid crystal cell. FIG. 4 is an explanatory diagram of the Brewster angle, FIG. 5 is an explanatory diagram of operation under pulse excitation, and FIG. 6 is a diagram showing the main points of the laser oscillator according to the second embodiment of the present invention. Part configuration diagram, No. 7
The figure is a configuration diagram of main parts of a laser oscillator according to a third embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Laser medium, 2...Perfect reflecting mirror, 3...Output reflecting mirror, 4.13...Transmissive liquid crystal cell, 5...Optical axis, 6...Liquid crystal cell driver, 7 ...excitation power supply, 8
···lamp. 9... Control circuit, 12... Photoelectric conversion element, 14...
・Coating film.

Claims (8)

[Claims] 1. In a laser oscillator comprising a laser medium and a pair of reflecting mirrors facing each other with the laser medium in between, a transmissive liquid crystal cell is placed between one of the pair of reflecting mirrors and the laser medium. A laser oscillator characterized by being installed at a star angle. 2. In a laser oscillator comprising a laser medium and a pair of reflecting mirrors facing each other with the laser medium interposed therebetween, a transmission type liquid crystal cell provided between one of the pair of reflecting mirrors and the laser medium. A laser oscillator, characterized in that the laser oscillator is installed at an angle such that the linearly polarized light reflectance by the surface of the transmissive liquid crystal cell is 0.2% or less for the P-polarized light component and 11% or more for the S-polarized light component. 3. A reflecting mirror and a transmissive liquid crystal cell tilted at a required angle are arranged to face each other with a laser medium in between, and a highly reflective coating film is further provided on the laser beam exit side surface of the transmissive liquid crystal cell. A laser oscillator characterized by comprising an optical resonator. 4. 4. A laser oscillator according to claim 1, further comprising a control device that applies a liquid crystal drive voltage between transparent electrodes of a transmission type liquid crystal cell during a period in which the laser medium is excited. 5. 5. The laser oscillator according to claim 4, wherein the control device applies the liquid crystal drive voltage when the intensity of the S-polarized light component reflected by the transmission type liquid crystal cell reaches a predetermined value. 6. 6. A laser oscillator according to claim 1, wherein the transparent electrode of the transmission type liquid crystal cell has a thickness of 800 Å or less. 7. 7. A laser oscillator according to claim 1, wherein a glass substrate made of a low alkali material is used as a glass substrate constituting the transmission type liquid crystal cell. 8. A laser oscillator according to any one of claims 1 to 7, comprising a cooling means for a transmission type liquid crystal cell.