JPH07131098A - Shg solid-state laser light source - Google Patents

Abstract

PURPOSE:To amplitude-modulate an applied low voltage with an arbitrary pulse width by providing an electric pulse generator for applying a voltage to an SHG element, and a wavelength selector of a wavelength resolution limit value in an SHG wavelength on an SHG laser light emitting optical path. CONSTITUTION:A polarizing plate 4 made of a Brewster's plate and an SHG element 5 having an optical path surface AR-coated with two electrodes are provided in a laser oscillator having a solid state laser crystal 1 and a mirror 6 covered with a coating having low reflectivity for a high reflectivity SHG light of an oscillation light. An exciting LD 3 is driven by a drive power source 11, and the element 5 is driven by an electric pulse generator 8 of output 20V, and a Fabry-Perot etalon 7 having 50pm of 60% beam width resolution of reflectivity of a coated film in a band of 0.53mum of a wavelength is disposed on a laser emitting optical path from the mirror 6. Accordingly, if the wavelength resolution of the selector is about 100pm at least at the maximum, the amplitude intensity of the laser output light of the light source can be modulated by wide modulation band.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SHG (Second Harm) capable of modulating the amplitude intensity of laser output light applicable to a light source for reading an optical disk or the like with a wide modulation bandwidth.
onic Generation) solid-state laser light source.

[0002]

2. Description of the Related Art Conventionally, an internal resonance type SHG solid-state laser having a SHG element arranged in a semiconductor laser-excited solid-state laser resonator is known as a small-sized laser light source capable of highly efficiently emitting green or blue light. Has been. An electrode is attached to the SHG element of this internal resonance type SHG solid state laser,
An example of applying a high voltage of 0 V or more to modulate the laser output is reported by equality in Proceedings of the 1992 Spring Applied Physics Association Joint Lecture Proceedings Vol. 3, 31a-D-7.
According to this report, Q-switched laser oscillation with a repetition rate of 1 kHz and a pulse width of about 40 ns is realized in an internal resonance type SHG solid state laser composed of an Nd: YVO ₄ crystal, a KTP crystal and an output mirror. The laser output characteristics obtained by this method are suitable for laser processing such as conventional trimming of semiconductor elements and the like.

In the case of a read / write light source for an optical disk, there is an example in which an ultrasonic modulator is provided on the emission optical path of a continuous oscillation type internal resonance type SHG solid state laser to realize on / off modulation of output light. ISOM / ODS 'of the year
93 Proceedings (Conference Digest o
f Joint Inter-national Sy
mposium On Optical Memory
And Optical Data Storage
1993) 8 pages. It is shown that this method can modulate up to a modulation frequency band of 13 MHz.

[0004]

However, in the above method of performing modulation in the resonator, the oscillation state is controlled by the presence or absence of an applied voltage between the oscillation state and the non-oscillation state. Due to the storage function, there is a drawback that the output pulse width and the peak output fluctuate greatly depending on the modulation repetition frequency. Further, a voltage modulator of about 700 V is expensive, and it is difficult to obtain a high modulation frequency of kHz or higher.

Further, the above-mentioned method using the external modulator has drawbacks such as an expensive external modulator and a large power consumption of the modulator.

An object of the present invention is to provide an internal resonance type SHG solid-state laser light source capable of amplitude modulation of an output having an arbitrary pulse width with a low applied voltage, low power consumption, simple structure, and low cost. It is to be.

[0007]

According to the present invention, a birefringent filter including a polarizing element and an SHG element provided in a laser resonator and a solid-state laser element excited by an excitation light source are arranged inside. A resonance type SHG solid-state laser, characterized in that an electric pulse generator for applying a voltage to the SHG element and a wavelength selection element having a wavelength separation ability of 100 pm or less at the SHG wavelength are provided on the emission optical path of the SHG laser light. It is an SHG solid-state laser light source.

[0008]

The principle of the present invention will be described. Conventionally, internal resonance type S
In the HG solid state laser, a polarizing element and SH are placed inside the resonator.
It is known that a single longitudinal mode oscillation can be achieved by providing a birefringent filter composed of a G element. Also,
It is also known that an electrode is provided on the SHG element and a high voltage pulse corresponding to a 1/2 wavelength voltage is applied to cause Q switch oscillation.

According to the present invention, based on the electro-optical effect of the SHG element, the oscillation wavelength of the internal resonance type SHG solid state laser is set to a wavelength change rate of about 1/10000, and the distance between adjacent longitudinal modes of the laser resonator is about the same. To change it, 1/10 of the 1/2 wavelength voltage used in normal Q-switch oscillation
The following small voltage is required, and further, in the case of the internal resonance type SHG solid-state laser oscillator, the oscillation wavelength does not change but the oscillation does not stop. It was made based on the new finding that the fluctuation of the peak output can be reduced.

Since the change of the oscillation wavelength of the fundamental wave is converted to the SHG light as it is by only halving the wavelength, the SH
In order to amplitude-modulate the laser output of G light, a wavelength selection element such as an etalon having a high resolution that can separate wavelengths corresponding to adjacent longitudinal mode intervals in the wavelength of SHG light may be arranged on the emission optical path. In the case of an internal cavity type SHG solid state laser used as a light source for reading and writing optical discs, the optical path length of the laser cavity is usually about 15 mm, and the adjacent longitudinal mode interval of SHG light corresponding to the cavity length is about 5 pm. Therefore, if the wavelength resolution of the wavelength selection element outside the laser resonator is usually higher than 50 pm, the effect of the present invention can be obtained. Therefore, the wavelength resolution of the wavelength selection element used in the present invention is within a range in which the practicality is not impaired if the wavelength resolution of at most about 100 pm is taken into consideration, even in consideration of the possibility of further shortening the optical path length of the laser resonator. Therefore, it is considered that the present invention can be effectively implemented.

[0011]

Next, the operation of the present invention will be described in detail with reference to an embodiment of the present invention. FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

The light emitted from the exciting semiconductor laser 3 is the lens 2
Thus, the solid-state laser crystal 1 made of Nd: YVO ₄ crystal having a thickness of 1 mm is focused and the solid-state laser crystal 1 is excited. On the semiconductor laser side, the solid-state laser crystal 1 transmits 98% of the excitation light, and the oscillation light in the 1.06 μm band is 99.99.
% Reflective dichroic coat is applied, and the other side is
An AR coating is applied to the oscillation light. A polarizing plate 4 formed of a Brewster plate is provided in a laser resonator including a solid laser crystal 1, a mirror 6 having a high reflectance for oscillating light and a low reflectance for SHG light, and an optical path surface. An SHG element 5 which is AR-coated and made of a KTP crystal provided with two electrodes is provided. A Fabry-Perot etalon 7 having a coating film reflectance of 60% and a line width resolution of 50 pm in the wavelength band of 0.53 μm is arranged on the laser emission optical path from the mirror 6. The etalon 7 is a parallel plate glass substrate having both surfaces coated with reflection coating. Etalon 7
The peak wavelength of the transmittance is 0 when the voltage applied to the SHG element 5 is 0.
In this case, the inclination of the etalon 7 and the optical axis is adjusted in advance so that it becomes the maximum at. The transmittance curve of the etalon 7 at this time is shown in FIG.
It shows in (a). The laser oscillator and the etalon 7 are housed in a container 9, and the entire temperature is kept at a constant temperature by a temperature controller 10 with an accuracy of 0.1 ° C. The excitation LD 3 is driven by the drive power supply 11, and the SHG element 5 outputs 20V.
Driven by the electric pulse generator 8 of.

The size of the SHG element 5 is 1 × 3 × 7 mm
Then, the electrode was attached in the direction of a thin thickness of 1 mm. The direction in which the electric field is applied is in the C-axis direction of the crystal. In this state, the container temperature is 25 ° C., and the output of the LD3 for excitation is 300 mW.
An operation experiment was performed by changing the voltage applied to the HG element 5.

FIG. 2 is a diagram showing static operating characteristics.
(A) shows the wavelength transmittance characteristics of the elalon 7, and FIG.
(B) is a diagram showing a voltage applied to the SHG element 5 and a wavelength change of the emitted SHG light. It was found that the oscillation wavelength discretely hops at intervals of 0.1 nm as the applied voltage increases. From this characteristic and the transmittance curve of the etalon 7 in FIG. 2A, when the voltage applied to the SHG element is 0, the output of the SHG light from the etalon 7 becomes maximum, and the applied voltage is 30V.
It can be seen that the output becomes minimum when. The SHG outputs at wavelengths λ ₁ and λ ₂ were 30 mW and 10 mW, respectively, and the powers required for writing and reading data on the optical disc were obtained.

Next, a high-frequency characteristic was examined by applying a pulse voltage to the SHG element 5 from the electric pulse generator 8. The SHG output waveform follows up to a pulse modulation frequency of 50 MHz, and the rising and falling times of the SHG output are 20 ns and 25 ns, respectively, and a modulation characteristic sufficient for optical disk applications was obtained. Also, the repetition frequency,
The SHG peak output could be kept constant regardless of the pulse duty ratio. The upper limit of the modulation frequency is the internal resonance type S
It is considered that the HG solid-state laser is close to the upper limit frequency determined by the resonator lifetime of 10 ns and is limited by the resonator lifetime.
Since the photon lifetime of the etalon 7 is as short as 1 ns or less, it does not affect the modulation characteristics. The power consumption of the electric pulse generator is 200 at most because the SHG element 5 has a low capacitance load of about 10 pF and the applied voltage is as low as about 20V.
The power consumption was mW, and the power consumption could be reduced by one digit or more as compared with the conventional ultrasonic external modulator and high voltage Q-switch modulator.

[0016]

According to the present invention, the amplitude modulation of the output having an arbitrary pulse width up to about 50 MHz can be performed with a low applied voltage of about 10 V, the power consumption is small, the configuration is simple, and the cost is low. An internal cavity type SHG solid state laser light source can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a device configuration according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the present invention, in which (a) is a diagram showing wavelength transmittance characteristics of an etalon, and (6) is a diagram showing a relationship between laser output wavelength change and applied voltage.

[Explanation of symbols]

 1 Solid-state laser crystal 2 Lens 3 Excitation LD 4 Polarizing plate 5 SHG element 6 Mirror 7 Etalon 8 Electric pulse generator 9 Container 10 Temperature controller 11 Driving power supply

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01S 3/10 A 3/106

Claims (1)

[Claims] 1. An internal-resonance-type SHG solid-state laser comprising a birefringent filter including a polarizing element and an SHG element provided in a laser resonator, and a solid-state laser element excited by an excitation light source. An SHG solid-state laser light source, comprising: an electric pulse generator for applying a voltage to the SHG element; and a wavelength selection element having a wavelength resolution of 100 pm or less at the SHG wavelength on the emission optical path of the SHG laser light.