JPH03222379A - Solid-state laser device - Google Patents

Abstract

PURPOSE:To enable a laser ray source which outputs laser rays of specified wavelength and output power to be offered by a method wherein a pumping light is fed, the wavelength of the pumping light is monitored, the drive current of a means which supplies the pumping light is made to change so as to obtain the pumping light of required wavelength, and an attenuation means placed in an optical path is electronically controlled in absorption characteristics. CONSTITUTION:Three photodetectors 21, 22, and 23 adjacent to one another are arranged in the optical path of diffracted light so as to enable light of required wavelength to be incident on the central photodetector 22 at an angle of prescribed diffraction order, and the drive current of a laser diode 3 is so controlled as to make the optical signal from the photodetector 22 maximal. The direction of the optical signal change can be judged by the optical signals of the photodetectors 21 and 23. The output change of the photodetector 22 attendant on the change of the drive current is so compensated by a liquid crystal attenuator 25 placed in the optical path as to make the output constant. That is, the liquid crystal is made to change in transmittance by adequately adjusting a voltage applied to the liquid crystal corresponding to the output change of a laser diode attendant on the change of the drive current to keep the transmitted light constant.

Description

[Detailed description of the invention]

[Industrial Application Field 1] The present invention relates to a solid-state laser device oscillated by laser diode pumping. [Conventional Technique v#3] One of the attempts to obtain a compact, constant output, constant wavelength, and highly efficient visible light source is a solid-state laser device that performs frequency-doubled oscillation by pumping with a laser diode. Attempts to oscillate solid-state lasers using laser diodes for pumping began in the mid-1960s. At that time, side-pumping type lasers were the norm, and various solid-state laser devices were considered. Early typical lasers required the laser diode to be cooled to very low temperatures in order to obtain pump light with a wavelength that matched the absorption lines of the laser medium. Many solid-state laser media emit light in the near-infrared.
It was pumped by an IAs laser diode. One of the leading candidates for this type of laser medium is one that uses a laser medium containing Nd3+ ions in some kind of matrix, the most successful of which is Y3Al, 012 (y AG) containing Nd3+ ions. ) is a solid-state laser device using This material has a large gain cross section and is arguably the most efficient solid state laser device available today. This material has a strong absorption peak near a wavelength of 809 nm. That is, this wavelength is the normal G a A I A s
It is within the oscillation wavelength range of the laser diode. This type of solid-state laser again attracted a lot of interest in the early 1980s, when high-power laser diodes or laser diode arrays that could emit light at room temperature in the above wavelength range became available. . Also, as high power laser diodes or laser diode arrays were developed, interest turned to end pumping. Today, solid-state lasers of this type are already available and commercialized. FIG. 2 shows a conventional device configuration for matching the emission wavelength of a pumping laser diode to the absorption line of a laser medium of an end-pumped laser diode pumping solid-state laser. In this device, a temperature control device 1, a Peltier device 2
By adjusting the temperature of the pumping laser diode 3, the emission wavelength of the laser diode 3 is controlled. The laser diode 3 is attached to a heat sink 4 and its temperature is monitored by a temperature sensor 5. Laser light from the laser diode 3 is collimated by a collimator 6 and focused onto the end face of a laser rod 7 by a condenser 8 . In this device, single wavelength operation is maintained while the laser diode drive current remains unchanged. In short, the radiant energy source O is located at the reference plane 0x in Cartesian coordinates.
A light beam 9 is emitted along the axis Ox of vz. A collimator 6 collimates the diverging light, and the collimated light beam 9 is further focused onto a laser medium 7 by a condenser 8 . The laser medium 7 is placed between two resonant mirrors 10.11. Effective laser oscillation can be achieved by matching the resonator mode to the focused spot using an appropriate optical system. Matching the emission wavelength of the laser diode 3 to the absorption line of the laser medium 7 is done by the Peltier element 2 and the temperature controller 1 as described above. [Problems to be Solved by the Invention] However, one major problem with solid-state lasers such as the conventional example described above is how to effectively match the wavelength of the pumping light to the narrow absorption line whose half-width is only about 3 nm. , the problem is maintaining that state. Generally, the wavelength of the light used for bombing is required to match a strong absorption line in the laser medium. The reason for this is that efficient absorption of pumping light by the laser medium increases the efficiency of laser oscillation. As mentioned above, in the field of solid-state lasers, matching the wavelength of the light used for bombing and the absorption spectral lines of the laser's active medium is a major technical challenge. A common solution today to the above problem is to use a suitable temperature control device, for which purpose a Peltier device is used. This is based on the principle that by controlling the temperature of a laser diode, its oscillation wavelength can be controlled. In this case, in order to keep the laser oscillation wavelength constant, the drive current must be kept constant. However, such a system has two problems. First, the Peltier device itself is bulky, expensive, and requires a complex drive system. This means that electronic equipment for temperature detection is required. Additional power is then required to operate the Peltier device, which may require one ampere or more for devices using high power laser diodes or laser diode arrays. These increase the size of the laser device as a whole. The second problem is that when the laser drive current is changed to reduce the output of the laser, the emission wavelength of the laser generally also changes. This means that as the driving current of the pumping laser diode changes,
This is undesirable because the wavelength of the pumping light deviates from the wavelength of the maximum absorption peak of the active medium (laser rod) to be used for laser oscillation. However, it can be said that a device having the above configuration using a Peltier device for stabilizing the drive of a laser diode has feasibility as a solid-state laser device with a constant output and a constant wavelength. In addition, in devices that pump with laser light pulsed at a low repetition rate, thermal problems associated with laser heat generation, which are always a problem with laser devices that perform continuous pumping, are alleviated, and the solid-state laser device can oscillate continuously. becomes possible. That is, the fact that the upper limit of the lifetime of the Nd:YAG crystal is on the order of milliseconds means that the pumping period is substantially rectified and continuous wave oscillation is possible with only a slight fluctuation (ripple) in the output. It means that. However, in the conventional example described above, the continuous oscillation described above does not work because the operating wavelength of the laser diode changes when the ambient temperature changes. The present invention has been made to solve the problems in the prior art described above. That is, an object of the present invention is to provide a laser light source that can obtain a desired constant wavelength and a constant output. Another object of the present invention is to provide a laser light source that can maintain constant output and oscillation wavelength even under relatively large temperature changes. Still another object of the present invention is to provide a laser diode-pumped solid-state laser device that is not bulky, expensive, or reduces efficiency, and satisfies the above performance.

[Means to solve the problem]

The laser diode-pumped solid-state laser device of the present invention has means for matching the wavelength of the pumping laser diode with the steep absorption spectrum of the laser medium and maintaining it constant. Further, the laser diode pumping solid-state laser device of the present invention has means for changing the output of the pumping laser diode in order to stabilize the output of the solid-state laser. The basic configuration for achieving the above object in the present invention is as follows. (1) Appropriate spectroscopic means is used as means for monitoring the emission wavelength of the pumping laser diode. For example, an appropriate photodiode is used to detect the position of the light beam from the spectroscopic means. (2) A driving current variable means is used to control the emission wavelength of the pumping laser diode, and the output change accompanying the change in the driving current of the laser diode is used to control the emission wavelength of the pumping laser diode. The laser diode's own inherent polarization is used to compensate by attenuating the output from the laser diode in the optical path.

[Effect]

That is, since the emission angle of the light beam from the spectroscopic means depends on the angle of incidence of the light beam on the spectrometer and the wavelength of the light beam, a signal representing the position of the beam is detected by a photodiode, etc., and a predetermined incident angle is detected. By knowing the exit angle of the light beam from the spectroscopic means under the angle, the emission wavelength of the pumping laser diode can be monitored. Furthermore, since the transmittance of the laser beam to the liquid crystal can be adjusted by changing the voltage applied to the liquid crystal, the output of the laser diode can be electronically adjusted to 1lffi by using the liquid crystal and the means for applying a variable voltage to the liquid crystal. be able to.

【Example】

FIG. 1 shows the basic structure of an apparatus according to an embodiment of the present invention, which solves the problems of the prior art described above. In the figure, the laser diode 3 is itself mounted on a heat sink 4 which is cooled as efficiently as possible by the usual means of conduction and convection. In this example, the diode 3 emits laser light from the two open faces of the laser, and the emitted light 12 from the rear face is collimated by a second collimator 13, resulting in a light beam 1
4 is guided to a spectrometer, such as a diffraction grating 15. The light incident on the diffraction grating 15 is separated according to different orders of diffraction. In this figure, the O-order light 16 is m=o, and the two primary lights 1
7.18 is represented by m=1, and two secondary lights 19.20 are represented by m=2. A change in the operating wavelength of the laser diode results in a shift in the diffraction angle of each of these orders. The relationship between the diffraction angle θ, the wavelength λ, and the diffraction order m is given by the following equation (1). d sinθ=mλ ・・・・・・・・・(
1) Here, d: lattice constant (distance between lattice) Therefore, the diffraction angle of each diffraction order changes in response to a change in wavelength. d λ a cosθ This formula shows that the angle change in high-order diffracted light is
This means that it is highly sensitive to changes in wavelength. In addition, the smaller the grating constant of the diffraction grating 15, in other words, the higher the grating density, the higher the sensitivity. Here, similar wavelength monitoring is possible by using other spectroscopy means such as a prism in place of the diffraction grating 15. By placing an appropriate photodetector in the optical path of the diffracted light, the emission wavelength of the laser diode is monitored. Three photodetectors 21, 22 and 23 adjacent to each other are arranged in the optical path of the diffracted light so that light of a desired wavelength is incident on the central detector 22 at an angle of a predetermined diffraction order. The driving current of the laser diode 3 is adjusted so that the optical signal from the central photodetector 22 is maximized. Then, the direction of change in the drive current is determined by the other two photodetectors 21 and 2.
It can be determined from the optical signal of No. 3. Changes in the output due to changes in the driving current of the laser diode 3 are compensated for to a constant output by suitable attenuating means 25, such as a liquid crystal, placed in the optical path. That is, by appropriately adjusting the voltage applied to the liquid crystal, the transmittance of the liquid crystal is changed in accordance with the change in the output of the laser diode due to the change in the drive current, and the intensity of the transmitted light is kept constant. Here, in this figure, 24 indicates a collimator, and 25 indicates a liquid crystal. FIG. 3 is a block diagram showing an example of the configuration of an electronic feedback mechanism used in an embodiment of the present invention. The laser drive device 27 is associated with the liquid crystal 25 and includes a photodetector 21 to control the drive current of the laser diode 3.
．． The photoelectric output of 22.23 is monitored. block 28
The electronic device group shown by automatically applies an appropriate voltage to the liquid crystal 25. FIG. 4 shows temporal changes in the drive current of the laser diode (a) and the output of the solid-state laser (b) in a state where the temperature of the pumping laser has been stabilized. Although an example in which the drive current is set in pulse drive mode is shown here, it is of course possible to set the drive current in continuous wave drive mode. The wavelength stability of the pumping laser light is very good in pulse drive mode under constant temperature. However, when the ambient temperature of the laser diode changes, the above wavelength stability cannot be maintained as it is. According to the configuration of the embodiment shown in FIG. 1, when a change in the emission wavelength of the laser diode due to a temperature change is detected, the drive current is changed so that the original wavelength is obtained, and the drive current is adjusted to the change in the drive current. The accompanying output changes can be compensated for by controlling the transmitted light intensity to be constant by changing the voltage applied to the liquid crystal, making the solid-state laser a constant wavelength and constant energy source regardless of changes in ambient temperature. It can be bombed with light. Here, the configuration shown in FIG. 1 can be modified in accordance with the principles of the present invention, including how to install the diffraction grating in the optical path of the light beam, how to combine and set photodetectors corresponding to various orders of diffraction, etc. Of course, modifications are possible. The solid-state laser device of the present invention as described above can also be applied as a device for measuring the absorption characteristics of the laser medium itself in a spectral range close to the emission wavelength spectrum of a laser diode, for example. Through such applications, it is possible to easily evaluate whether various crystals are effective as laser media. [Effects of the Invention] As described above, according to the present invention, a desired constant wavelength and a constant output can be obtained, and the output and oscillation wavelength can be maintained even with a relatively large temperature change of the laser medium. It is possible to provide a laser device that can maintain a constant value. Furthermore, a compact, highly efficient, and inexpensive solid-state laser device can be provided.

[Brief explanation of drawings]

Figure ↓ is a schematic diagram showing the configuration of the pumping mechanism of a solid-state laser device according to one embodiment of the present invention, Figure 2 is a schematic diagram showing the schematic configuration of a conventional solid-state laser device, and Figure 3 is a schematic diagram showing the configuration of the pumping mechanism of a solid-state laser device according to an embodiment of the present invention. FIG. 4 is a block diagram showing an example of the configuration of an electronic feedback mechanism used in the embodiment. Each is a graph showing changes over time. Explanation of symbols 1... Temperature adjustment device, 2... Peltier element, 3...
...Laser diode, 4...Heat sink 5.
...Temperature sensor, 6.13.24...Collimator, 7...Laser rod, 8...Concentrator, 9 Light beam, 10.11...Resonance mirror 15...Diffraction grating, 21 .22.23...Photodetector, 25...
・LCD, Sozuzu Karo (0-) 3 Yukoku (e) (b)

Claims (1)

[Claims] 1. Means for supplying pumping light, means for monitoring the wavelength of the pumping light, and means for changing the driving current of the means for supplying pumping light so as to obtain pumping light of a desired wavelength. and attenuating means placed in the optical path of the emitted pumping light, means for electronically controlling the absorption characteristics of the attenuating means, and a solid laser medium for causing laser oscillation with the light transmitted through the attenuating means. A solid-state laser device. 2. The solid-state laser device according to claim 1, wherein the means for monitoring the wavelength comprises appropriate spectroscopic means and means for detecting a change in the emission angle of light from the spectroscopic means. 3. The solid-state laser device according to claim 2, wherein the spectroscopic means comprises a diffraction grating. 4. The attenuation means is
2. The solid-state laser device according to claim 1, wherein the solid-state laser device is made of liquid crystal. 5. The solid-state laser device according to claim 1, wherein the means for supplying the pumping light comprises a laser diode or a laser diode array.