JPH0590672A - LD pumped solid state laser - Google Patents

Abstract

(57) [Abstract] [Purpose] Even if the driving conditions such as the output power of the pumping laser diode are changed or the characteristics change over time, a constant oscillation wavelength is always obtained following these changes.
An LD pumped solid-state laser capable of obtaining a stable output is provided. [Structure] A part of the output light of the pumping laser diode is extracted and dispersed, the dispersed light is guided to a two-channel photodiode, and the deviation of the oscillation wavelength from the target wavelength is detected, and the laser is based on the result. Feedback control the temperature of the diode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pumping type solid-state laser using output light of a laser diode.

[0002]

2. Description of the Related Art In a solid-state laser excited by the light of a laser diode, generally, the excitation of a fixed medium such as Nd: YAG is sensitively dependent on the wavelength of the excitation light. Unless stabilized by the method, the output of the solid-state laser becomes unstable.
Therefore, in this type of conventional laser, a temperature controller for the laser diode for excitation is provided and the oscillation wavelength is stabilized by keeping the temperature constant, but the oscillation wavelength of a practical laser diode is It is also affected by the difference in the amount of heat generated due to the difference in the output or drive current.Therefore, after determining the output or drive current of the laser diode, the temperature controller described above should be used to obtain the desired oscillation wavelength of the laser diode. Is being adjusted.

[0003]

By the way, when it is desired to change the output of the solid-state laser, it is necessary to change the output of the laser diode for excitation. However, even if the output of the laser diode is changed, the oscillation wavelength is changed. Unless kept constant, the output of the solid-state laser cannot be stabilized. Here, if you want to operate the laser diode while changing the output power at the same wavelength, you can stabilize the wavelength of the laser diode by adjusting the temperature controller after knowing the relationship between wavelength, output, and temperature. Is being converted. Since it is impossible to monitor the temperature of the light emitting portion of the laser diode chip in a practical laser diode, it is necessary to change the set temperature in order to change the output power and keep the wavelength constant. Therefore, in the conventional technology, it is necessary to know the relationship between the wavelength, the output, and the temperature of each laser diode in advance, and a huge amount of time and effort is required to know the relationship between these characteristics before the control system is operated. I need. In addition, it is impossible to deal with such a change with time in characteristics.

The present invention has been made in view of the above point, and the oscillation wavelength of the pumping laser diode is automatically changed even if the output of the pumping laser diode is changed without investigating the relationship of the above characteristics in detail. Can be kept constant and
It is an object of the present invention to provide an LD pumped solid-state laser that can be automatically adjusted even if there is a change with time and can always obtain a stable output.

[0005]

In order to achieve the above object, in the present invention, a spectroscope for taking out a part of output light of a laser diode for excitation and separating the light, and a spectroscopic light of two channels. A detection circuit that detects whether the oscillation wavelength of the laser diode is short, long, or coincides with the preset wavelength when it enters the light receiving element, and the temperature of the laser diode is feedback-controlled based on the detection result. The control circuit is provided to keep the oscillation wavelength constant even if the driving conditions such as the current of the laser diode change.

[0006]

[Operation] When the oscillation wavelength of the laser diode for excitation matches the preset wavelength (target wavelength), the outputs of the two light receiving elements are balanced, but the oscillation wavelength of the laser diode is equal to the target wavelength. If deviated, the balance of the output of the light receiving element is broken. Also,
Since the magnitude relationship between the lasing wavelength and the target wavelength can be known depending on which of the outputs of the two-channel light receiving elements has increased,
By feeding back this information to the temperature controller of the laser diode and controlling the temperature of the laser diode so that the outputs of the two light receiving elements are balanced,
The oscillation wavelength of the laser diode for excitation can be kept constant.

[0007]

FIG. 1 is a configuration diagram of an optical system when the embodiment of the present invention is applied to an edge-pumped LD-pumped solid-state laser.
The output light of the laser diode 1 is applied to the Nd: YAG crystal 4 via the collimating lens 2 and the focusing lens 3, and is output to the outside as a solid-state laser light via the mirror 5. This structure is equivalent to the conventional one.

In the embodiment of the present invention, the beam splitter 6 is arranged between the laser diode 1 and the collimating lens 2, whereby a part of the output light of the laser diode 1 is extracted and the light is reflected by the reflection type grating 7. Is leading. A two-channel photodiode 8 is arranged on the detection surface of the reflection type grating 7, and the laser diode light dispersed by the reflection type grating 7 enters the two-channel photodiode 8.

The two-channel photodiode 8 is composed of two photodiodes PD1 and PD2 adjacent to each other, and the position of the boundary between the incident surfaces is adjusted so that the light of the target oscillation wavelength is detected. Has been done. Therefore, the light shifted to the shorter wavelength side than the target wavelength enters the one photodiode PD1, and the light shifted to the longer wavelength side enters the other photodiode PD2. The photocurrents of the photodiodes PD1 and PD2 are supplied to the signal processing circuit described below and used for temperature control of the laser diode 1.

FIG. 2 is a block diagram showing the configuration of the signal processing circuit according to the embodiment of the present invention. The photocurrents of the photodiodes PD1 and PD2 are input to the amplifiers 11 and 12, respectively, and converted into voltage signals, and then the amplifier 13
Is input to the laser diode 1 and is converted by the amplifier 13 into a signal indicating whether the oscillation wavelength of the laser diode 1 is shifted to the long wavelength side or the short wavelength side.

That is, when the oscillation wavelength of the laser diode 1 is deviated to the long wavelength side, the photodiode P
The photocurrent of D2 becomes larger than the photocurrent of the photodiode PD1, so that the positive input of the amplifier 13 becomes larger than the negative input, and the positive voltage signal is output from the amplifier 13. When the oscillation wavelength of the laser diode 1 deviates to the short wavelength side, on the contrary, a negative voltage signal is output from the amplifier 13. When the oscillation wavelength matches the target wavelength, the photocurrent outputs of the two photodiodes PD1 and PD2 match (or both become 0), and the output of the amplifier 13 becomes 0.

The output of the amplifier 13 is the temperature setting device 14
After being added to the normal temperature setting signal from, the temperature adjusting circuit 15 is supplied with the temperature setting signal. The temperature adjusting circuit 15 is configured to control the current flowing through the laser diode temperature adjusting Peltier element 16 according to the temperature setting signal thus supplied. With the above configuration, when the oscillation wavelength of the laser diode 1 deviates from the target wavelength, the set temperature in the temperature adjustment circuit 15 automatically changes according to the deviated direction. Specifically, a signal that lowers the set temperature when the oscillation wavelength shifts to the long wavelength side and a signal that raises the set temperature when the oscillation wavelength shifts to the short wavelength side are automatically supplied. As a result, the temperature of the laser diode 1 is adjusted by automatically following changes in driving conditions such as changes in the output power of the laser diode 1 and changes in characteristics over time, and the oscillation wavelength is always kept constant. Be drunk

Here, the 2-channel photodiode 8
The two light-receiving surfaces of the two photodiodes PD1 and PD2 are sufficiently long in the wavelength dispersion direction of the spectroscope (reflection grating 7 in the above example) to widen the detection range of the deviation amount of the oscillation wavelength from the target wavelength. By doing so, there is no need to investigate in advance the relationship between the wavelength, the temperature, and the output of the laser diode 1 used.

Further, the present invention can be applied to an LD pumped solid-state laser of the type that uses a large number of laser diodes as a pumping light source, and the wavelengths of the individual laser diodes can be matched by the method of the present invention. In this case, even if the selection of the oscillation wavelengths of the plurality of laser diodes is rough, the wavelengths are automatically controlled to a constant wavelength at the time of operation, and a stable solid-state laser can be obtained.

[0015]

As described above, according to the present invention, a part of the output light of the laser diode for solid-state laser excitation is extracted and dispersed, and the dispersed laser diode light is guided to the 2-channel photodiode. By doing so, it is detected that the lasing wavelength of the laser diode is shifted or matched to the long wavelength side or short wavelength side of the target wavelength, and the set temperature of the temperature adjustment circuit of the laser diode is detected based on the detection result. Because it changes automatically,
Even if the driving conditions such as the output power of the laser diode changes, or the characteristics change over time, the temperature automatically changes accordingly and the laser diode oscillation wavelength is always constant. Kept in.

As a result, not only is the solid-state laser output stable, but there is no need to previously investigate the relationship between the wavelength, output, and temperature of the pumping laser diode as in the conventional case, and
It is now possible to change the output power at any time without subtly adjusting the set temperature.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a signal processing circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Laser diode 2 Collimating lens 3 Focusing lens 4 Nd: YAG crystal 5 Mirror 6 Beam splitter 7 Reflective type Grating 8 ・ ・ ・ ・ 2-channel photodiode PD1, PD2 ・ ・ ・ ・ Photodiode 11, 12, 13 ・ ・ ・ ・ Amplifier 14 ・ ・ ・ ・ ・ ・ Temperature setting device 15 ・ ・ ・ ・ ・ ・ Temperature control circuit 16 ・ ・ ・Peltier element for laser diode temperature control

Claims (1)

[Claims] 1. In a laser for exciting a solid-state laser medium by output light from a laser diode, a spectroscope for extracting a part of the output light of the laser diode and separating it, and a light receiving element of two channels for the separated light. Incident on the laser diode to detect whether the oscillation wavelength of the laser diode is shorter, longer, or coincident with the preset wavelength, and the temperature of the laser diode is feedback controlled based on the detection result. An LD-pumped solid-state laser comprising a control circuit for controlling.