JPH06140706A - Solid laser equipment - Google Patents

Abstract

PURPOSE:To stably obtain single longitudinal mode oscillation, with simple resonator structure, without installing position adjusting mechanism for an optical element constituting a resonator, by installing a means for adjusting the pressure in a chamber. CONSTITUTION:A very little part of outputted laser light is branched with a sampling mirror 11, and detected with a photodiode 12. When the oscillation frequency of laser light is identical to the transmission frequency of an etalon 6, the intensity of a signal from the photodiode 12 becomes maximum. By controlling the pressure in a chamber 9 in the manner in which the signal becomes always maximum, while monitoring the pressure with a pressure gauge, the output of the laser light is made always maximum. Hence single longitudinal mode oscillation can be stably obtained, with simple resonator structure, without installing position adjusting mechanism for an optical element constituting a resonator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state laser device for end-pumping a solid-state laser medium using light from a semiconductor laser chip as excitation light.

[0002]

2. Description of the Related Art Conventionally, in a resonator in which a solid-state laser medium such as Nd: YAG is installed between a pair of resonator mirrors opposed to each other, one end face of the resonator is excited with light emitted from a semiconductor laser chip. There is a type of solid-state laser device that irradiates light as light to excite a solid-state laser medium, and this is known as a laser light source that is easier than a type of solid-state laser device that uses a rare gas lamp or the like as an excitation light source. In particular,
The second harmonic light of the semiconductor laser pumped solid-state laser device is highly useful as a green light source for high density optical discs and various measurements. The laser light used for these applications is
It is essential that the light has high quality such as low noise. It is well known that a laser that oscillates only at a single frequency called a single longitudinal mode laser is ideal when a laser is required to have particularly high quality light such as low noise.

General Nd: YA as a solid-state laser medium
To make the G laser a single longitudinal mode, there is a method of inserting a frequency discriminating element called an etalon into the resonator. FIG. 2A shows a structure of a solid-state laser device which is not a single longitudinal mode type of a semiconductor laser pumped solid-state laser.
(B) shows the structure of a single longitudinal mode type solid-state laser device using the etalon 6. In the solid-state laser device shown in FIG. 2A, the light emitted from the semiconductor laser chip 1 is collected by the condenser lens 2 and applied to the end face of the solid-state laser medium 4, whereby the light energy is applied to the solid-state laser medium 4. When laser light is accumulated and the settings of the resonator mirrors 3 and 5 satisfy the laser oscillation conditions, laser oscillation occurs. Normally, as shown in FIG. 3A, the oscillation wavelength of the Nd: YAG laser is 1064n.
This is a multimode oscillation in which several oscillation lines are seen near m.

On the other hand, FIG. 3B is a diagram showing the frequency dependence of the transmittance of the etalon, and the frequency at which the transmittance is maximum appears periodically. If the frequency with the maximum transmittance and the oscillation frequency of the laser are made to coincide with each other, single longitudinal mode oscillation in which only one of the multi modes is selected is generated (FIG. 3).
(C)). However, when the laser oscillation frequency does not match the maximum frequency of the etalon transmittance, the laser oscillation weakens or stops, as shown in FIG. 4C. In order to avoid this, the transmission frequency is conventionally tuned by tilting the etalon 6 with respect to the optical axis in FIG.
The state was as shown in (c). However, the position of the support mechanism for the solid-state laser medium 4 and the resonator mirrors 3 and 5 is
When it changes due to the influence of a change in temperature, the oscillation frequency of the laser changes, and the state shown in FIG. 3 changes to the state shown in FIG. 4, and the output of the laser beam fluctuates and oscillation stops.

As described above, the single longitudinal mode oscillation of the solid-state laser device using the etalon is extremely unstable.
Therefore, in order to eliminate this instability, the resonator mirrors 3 and 5 are supported by piezo electrostrictive elements to change the resonator length,
The oscillation frequency of the laser has also been adjusted to the transmission frequency of the etalon 6. However, with this method,
Since a position adjusting mechanism is required for both the etalon and the resonator mirror, the resonator structure is very complicated.

[0006]

SUMMARY OF THE INVENTION In view of the above problems of the prior art, the main object of the present invention is to provide a simple resonator structure without providing a position adjusting mechanism for an optical element constituting the resonator. The object of the present invention is to provide a semiconductor laser pumped solid-state laser device that stably obtains single longitudinal mode oscillation.

[0007]

A resonator comprising a pair of mirrors, a solid-state laser medium disposed in the resonator,
In a solid-state laser device including a semiconductor laser chip as a pumping light source for end-pumping the solid-state laser medium and an etalon for discriminating an oscillation frequency, in order to cover the resonator and hermetically seal the inside. Chamber of
And a means for adjusting the pressure in the chamber.

The principle underlying the present invention will now be described.

Between the gas pressure P and the density ρ, there is a well-known gas law.

[0010]

[Equation 1]

[0011] Here, R represents a gas constant and T represents temperature. Further, the following empirical formula is established between the refractive index n of the gas and the density ρ.

[0012]

[Equation 2]

Where β is a constant determined by the gas, ρ
_S is the density at 0 ° C. and 1 atm. Therefore, it can be seen from the above two equations that the refractive index n of the gas changes as the pressure P of the gas changes.

On the other hand, the following relational expression holds between the refractive index n of the gas and the oscillation frequency ν of the laser.

[0015]

[Equation 3]

Here, L is the cavity length, C is the speed of light in a vacuum, n is the refractive index of the medium filling the cavity, and m is a natural number.

From the above, it is understood that the oscillation frequency ν of the laser can be changed by changing the pressure P inside the resonator (in the present invention, inside the chamber). (Actually, the apparent resonator length nL changes due to the change of the pressure P in the chamber, and the laser oscillation frequency ν
Can be considered to change. )

[0018]

In this way, by providing the means for adjusting the pressure in the chamber, the oscillation frequency of the laser can be finely adjusted without adjusting the position of the optical element, and the transmission frequency of the etalon and the laser can be adjusted. The oscillation frequency can be matched.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic configuration diagram showing a solid-state laser device in an embodiment to which the present invention is applied. The solid-state laser medium 4 in this embodiment is Nd: YAG. AlGa
Excitation light emitted from the As-based semiconductor laser chip 1 (8
(08 nm) is collected by the condenser lens 2 and applied to the solid-state laser medium 4 to excite the solid-state laser medium 4 to generate spontaneous emission light (1064 nm). The spontaneous emission light radiated from the solid-state laser medium 4 is reflected by the resonator mirror 5 through the etalon 6, reversely travels through the original optical path, returns to the solid-state laser medium 4, and is guided in the solid-state laser medium 4. While being amplified by emission, the solid-state laser medium 4 is reflected by the resonator mirror coating 4a provided on the end face on the pumping side and reciprocates in the resonator. Thus, if the settings of the resonator mirror coating 4a and the resonator mirror 5 satisfy the conditions for laser oscillation, single longitudinal mode laser oscillation whose frequency is discriminated by the etalon 6 is generated. The oscillated single longitudinal mode laser light is output from the resonator mirror 5.

The solid-state laser medium 4, the etalon 6, and the resonator mirror 5 which form the resonator are fixed in a chamber 9 whose interior is hermetically sealed, and the solid-state laser medium 4 and the resonator mirror 5 are: It forms the window of the chamber 9. The chamber 9 is communicated with a pair of gas inlet and outlet pipes, and electromagnetic valves 7 and 8 are provided in each pipe. Here, the inlet pipe provided with the electromagnetic valve 7 is adapted to send air from the compressor 10 into the chamber 9, and the outlet pipe provided with the electromagnetic valve 8 regulates the amount of gas discharged from the chamber 9. It is supposed to do. The electromagnetic valves 7 and 8 are driven by the arithmetic circuit 13.

In order to stably maintain the single longitudinal mode laser oscillation, the following control operation is performed. The purpose of control is to adjust the apparent resonator length of the resonator fixed in the chamber 9 by adjusting the pressure in the chamber 9 so that the frequency of laser oscillation matches the transmission frequency of the etalon 6. . First, the output laser light is branched into a small amount by the sampling mirror 11 and detected by the photodiode 12. When the oscillation frequency of the laser light and the transmission frequency of the etalon 6 match, the photodiode 12
The signal strength from is maximum. Therefore, the output of the laser light is always maximized by controlling the pressure in the chamber 9 while monitoring the pressure in the chamber 9 so that this signal is always maximized.

Although Nd: YAG is used as the solid-state laser medium in this embodiment, the present invention is not limited to this, and other solid-state laser medium may be used. Moreover, by inserting a wavelength conversion element in the resonator of FIG.
Harmonic light can be obtained.

[0024]

As is apparent from the above description, according to the solid-state laser device of the present invention, the single longitudinal mode is realized by the simple resonator structure without providing the position adjusting mechanism of the optical element forming the resonator. Oscillation can be stably obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a solid-state laser device showing an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a solid-state laser device showing a conventional example, in which part (a) is a normal solid-state laser device that oscillates a laser beam that is not in a single longitudinal mode, and part (b) is a single solid-state laser device using an etalon. It is a solid-state laser device that oscillates a single longitudinal mode laser beam.

FIG. 3 is an explanatory diagram of single longitudinal mode oscillation using an etalon.

FIG. 4 is an explanatory diagram when the transmission frequency of the etalon is shifted.

[Explanation of symbols]

 1 Semiconductor Laser Chip 2 Condenser Lens 3 Resonator Mirror 4 Solid Laser Medium 4a Resonator Mirror Coating 5 Resonator Mirror 6 Etalon 7 Electromagnetic Valve 8 Electromagnetic Valve 9 Chamber 10 Compressor 11 Sampling Mirror 12 Photodiode 13 Arithmetic Circuit 14 Pressure Gauge

Claims (2)

[Claims] 1. A resonator comprising a pair of mirrors, a solid-state laser medium disposed in the resonator, a semiconductor laser chip as a pumping light source for end-pumping the solid-state laser medium, and an oscillation frequency discriminating device. And a chamber for covering the resonator and hermetically sealing the inside, and a means for adjusting the pressure in the chamber. apparatus. 2. The solid-state laser device according to claim 1, wherein at least one end face of the solid-state laser medium is provided with a cavity mirror coating.