WO2007015501A1

WO2007015501A1 - Green solid laser light oscillation method and oscillation device

Info

Publication number: WO2007015501A1
Application number: PCT/JP2006/315268
Authority: WO
Inventors: Tetsuo Harimoto
Original assignee: Yamanashi University
Priority date: 2005-08-04
Filing date: 2006-08-02
Publication date: 2007-02-08
Also published as: JPWO2007015501A1

Abstract

There is provided a green solid laser oscillation device using semiconductor laser excitation capable of significantly stabilizing a green solid state laser light and solving the problem of the green noise by a comparatively simple configuration. The green solid laser oscillation device includes: an excitation laser light source, a first solid laser medium arranged in a resonator for receiving a laser light from the excitation laser light source and oscillating a basic wave laser, and a second solid laser medium arranged in the resonator for receiving the basic wave laser light and oscillating green solid laser light. The green solid laser oscillation device further includes: first temperature control means for controlling the temperature of the first solid laser medium so that the basic wave laser light is in a single longitudinal mode, and second temperature control means for controlling the temperature of the second solid laser medium so that the oscillation of the green solid laser light has a maximum efficiency.

Description

Specification

Method and apparatus for oscillating green solid laser light

Technical field

TECHNICAL FIELD [0001] The present invention relates to an oscillation method and an oscillation apparatus for a Darling solid-state laser beam that uses laser light emitted from a semiconductor laser device as excitation light, and particularly to Darling solid-state laser beam free from green noise with maximum efficiency. The present invention relates to a method for oscillating green solid-state laser light and an oscillation device.

Background art

FIG. 5 is a diagram showing a configuration of a semiconductor laser-excited solid-state laser described in Japanese Patent Laid-Open No. 5-198870 (see Patent Document 1).

In the conventional semiconductor laser pumped solid-state laser shown in FIG. 5, the pumping laser beam L emitted from the pumping semiconductor laser device 1 is solid-stated in a laser resonator.

0

Enter the laser medium 2 and excite the solid laser medium to obtain the output laser beam L

2

At the same time, when the solid-state laser medium 2, the laser resonators 3 and 4, and the functional optical element 5 are used, the functional optical element 5 is mounted on the same thermal conductive substrate 7 and the temperature of the thermal conductive substrate 7 is set. The temperature control devices 7a and 7b for controlling the temperature are provided.

Similarly, as a laser resonator including a solid-state laser medium 2 is cooled by using a Peltier element, Japanese Patent Laid-Open No. 2000-349370 (see Patent Document 2) or Japanese Patent Laid-Open No. 8-32160 (Patent Document 3). See). A ball lens as a condensing lens used in the present invention is described in JP-A-6-77560 (see Patent Document 4). Patent Document 1: Japanese Patent Laid-Open No. 5-198870

Patent Document 2: JP 2000-349370 A

Patent Document 3: JP-A-8-32160

Patent Document 4: JP-A-6-77560

Disclosure of the invention

Problems to be solved by the invention

[0005] In a green solid-state laser device using semiconductor laser excitation, a solid-state laser medium 2 and A solid-state laser crystal (Nd: YVO crystal) disposed in the laser resonator, and

Four

A combined wavelength conversion crystal (KTP crystal) is generally used.

In such a semiconductor laser pumped solid-state laser, the pumping laser beam L emitted from the pumping semiconductor laser device 1 is fixed in a laser resonator as described above.

0

The solid laser medium 2 is excited to obtain the output laser beam L.

Therefore, the temperature of the solid-state laser medium 2 is controlled by a temperature control device that controls the temperature of the heat conductive substrate 7 on which the solid-state laser medium 2 is mounted. Even if the solid-state laser medium 2 is excited and changes in temperature, the temperature of the solid-state laser light is kept constant within a predetermined range by keeping these temperatures constant. RU

[0007] However, in recent years, the use of green solid-state lasers excited by semiconductor lasers has further expanded, and along with this, the characteristics of green laser light such as the intensity of the green laser light and the longitudinal and transverse modes have increased. As a result, more stable output characteristics are required.

[0008] In a resonator of a green solid-state laser device excited by a semiconductor laser, there is a medium (solid-state laser crystal) for laser oscillation (fundamental wave generation) and nonlinear optics for wavelength conversion (second-harmonic generation). Contains crystals (wavelength conversion crystals). However, if the basic structure of the green solid-state laser device is a solid-state laser crystal and a wavelength conversion crystal, the fundamental wave oscillated from the solid-state laser crystal becomes multi-longitudinal mode oscillation, and the second output that is the laser output due to the interference effect between longitudinal modes. Harmonics change periodically with time, and stable output cannot be obtained. This is called green noise and is one of the causes of instability of laser output.

[0009] As a solution to the strong green noise problem, a method of inserting a quarter-wave plate in the resonator to eliminate coupling between modes, a method of obtaining single longitudinal mode oscillation with a ring resonator, or an etalon is used. A method of inserting a single laser between a solid-state laser crystal and a wavelength conversion crystal to forcibly oscillate a single longitudinal mode has been considered. However, these methods have a problem that it is difficult to take advantage of the small size of the green solid laser device and the cost of the device is high.

Accordingly, an object of the present invention is to provide a green solid-state laser oscillation device and a green solid-state laser light oscillation method that take advantage of the small size of the green solid-state laser device and do not increase the cost. Means for solving the problem

[0011] As a result of many years of research, the inventor considers that it is indispensable to make the fundamental wave a single longitudinal mode oscillation in order to suppress green noise, and laser oscillation ( Focus on the temperature dependence of the medium (solid laser crystal) for fundamental wave generation (non-linear laser crystal) and the nonlinear optical crystal (wavelength conversion crystal) for wavelength conversion (second harmonic generation). By optimizing the temperature conditions for generation, we realized a method for oscillating highly efficient and stable green solid-state laser light.

That is, according to the present invention, an excitation laser is incident on a first solid-state laser medium disposed in a laser resonator to oscillate a laser fundamental wave, and the laser fundamental wave is disposed in the laser resonator. In the method of oscillating green solid-state laser light that is incident on the second solid-state laser medium and oscillates the green solid-state laser light, the first solid-state laser medium is oscillated so that the laser fundamental wave oscillates in a single longitudinal mode. The temperature of the second solid-state laser medium wavelength conversion crystal is adjusted such that the temperature is adjusted and the oscillation efficiency of the green solid-state laser light is maximized.

The temperature of the second solid laser medium wavelength conversion crystal is adjusted by adjusting the temperature at which the laser fundamental wave has a maximum efficiency within the temperature range of the first solid laser medium in which single longitudinal mode oscillation occurs. It is preferable that

[0014] The present invention provides an excitation laser light source, a first solid-state laser medium that is disposed in a resonator, receives laser light from the excitation laser light source, and oscillates fundamental laser light, and in the resonator And a second solid-state laser medium wavelength conversion crystal that receives the fundamental laser beam and oscillates the green solid-state laser light, wherein the first solid-state laser medium oscillates the fundamental First temperature adjusting means for adjusting the temperature of the first solid-state laser medium so that the wave laser beam is in a single longitudinal mode, and the second solid-state laser beam so that the oscillation of the Darling solid-state laser beam has maximum efficiency. And a second temperature adjusting means for adjusting the temperature of the solid-state laser medium.

[0015] The present invention provides an excitation laser light source, a first solid-state laser medium that is disposed in a resonator, receives laser light from the excitation laser light source, and oscillates fundamental laser light, and the resonance Placed in the chamber to receive the fundamental laser beam and oscillate green solid laser beam In a green solid-state laser oscillation device including a second solid-state laser medium, the fundamental laser beam oscillated by the first solid-single-body laser medium is set to a single longitudinal mode.

Temperature adjusting means for adjusting the temperature of the first solid-state laser medium and adjusting the temperature of the second solid-state laser medium within the temperature range so that the oscillation of the green solid-state laser light has maximum efficiency. It is characterized by having.

The invention's effect

According to the present invention, it is possible to obtain a green solid-state laser device in which green noise is greatly suppressed and stable green laser light is emitted. Further, according to the present invention, single longitudinal mode oscillation can be realized without inserting a new optical component or the like in the laser resonator, and a small and low-cost green solid-state laser oscillation device can be obtained.

Brief Description of Drawings

FIG. 1 is a schematic view showing one embodiment of a semiconductor laser-pumped green solid-state laser device that works on the first embodiment of the present invention.

FIG. 2 is a graph showing the time distribution of the output power of green solid-state laser light.

FIG. 3 is a graph showing an output mode.

FIG. 4 is a graph showing a single longitudinal mode.

FIG. 5 is a schematic view of a conventional semiconductor laser pumped solid-state laser device.

Explanation of symbols

Semiconductor laser device for excitation

12 Pumping semiconductor laser

13 Bonorelens

14 Lens cap

15 Solid-state laser medium

15--1 Solid state laser crystal (first solid state laser medium)

15--2 wavelength conversion crystal (second solid-state laser medium)

16 Peltier Temperature control element

17 Temperature controller

18 Temperature sensor 21 Selective reflective film

22 Detector

23 Beam Splitter

24 Fabry-Perot scanning interferometer

L Excitation laser light

0

L fundamental wavelength laser light

1

L Green laser light

2

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail. The method for oscillating green solid laser light according to the present invention includes a pump laser beam emitted from a pumping semiconductor laser, a solid-state laser crystal arranged in a laser resonator, and a wavelength conversion crystal coupled and integrated therewith. The green laser light is obtained by making the solid laser medium incident through a ball lens and exciting the solid laser medium.

[0020] A solid-state laser crystal disposed in the laser resonator and a wavelength conversion crystal coupled and integrated with the solid-state laser crystal are mounted on a thermally conductive support having a Peltier temperature control element force. The temperature is controlled to a predetermined temperature by a temperature control device.

The refractive indexes of the solid-state laser crystal and the wavelength conversion crystal are sensitive to temperature, and the refractive index value changes as the temperature changes. The longitudinal mode V of laser oscillation is the force given by the relation V = mc / 2 (n d + n m m L L N d), where m is a positive integer representing the number of longitudinal modes, c is the speed of light, n and n are

N and N Refractive index of solid laser crystal and wavelength conversion crystal, d and d are solid laser crystal and

L N

This is the length of the wavelength conversion crystal. When the temperature changes, n and n change, and the oscillation frequency V also changes.

L N m Changes with this. Therefore, by adjusting the longitudinal mode closest to the maximum laser gain to the maximum gain, single longitudinal mode oscillation can be achieved by gain competition.

[0022] On the other hand, the conversion efficiency of the second harmonic wave generated by the wavelength conversion crystal (green laser light), the function (sin (A kd / 2) / (A kd / 2)) is proportional to ^2. Where A k is the phase mismatch factor and T

N N

In the phase matching method of ype II, it is given by the expression A k = co (n + n−2n) / c. Where ω is le lo 2e

Angular frequency of fundamental laser beam, _n , _n , _n are extraordinary ray fundamental wave and ordinary ray fundamental wave, respectively Refractive index of wave, extraordinary ray second harmonic. In order to obtain high conversion efficiency, the phase matching condition (Δ k = 0) must be satisfied. By changing the crystal temperature, the refractive index of the crystal also changes, and the wavelength conversion crystal is fixed at the temperature closest to the conditions of n + n -2n = 0 and A k = 0.

When heated, a highly efficient and stable green laser beam can be obtained. The temperature control by the Peltier temperature control element is preferably controlled within the temperature range of ± o.o e.

. As described above, by controlling the temperature of the solid-state laser crystal and the wavelength conversion crystal, high-efficiency green solid-state laser light can be obtained without including green noise.

Example

FIG. 1 is a block diagram showing a configuration of a green solid state laser device 11 of the present invention. The Darren solid-state laser device 11 includes an excitation semiconductor laser 12, a lens cap 14, a ball lens 13, a solid-state laser crystal 15-1, a wavelength conversion crystal 15-2, and a Peltier temperature control element 16.

An excitation laser is incident on the solid-state laser medium 15 in the laser resonator from the semiconductor laser 12 through the ball lens 13. In this embodiment, the solid-state laser medium 15 uses an Nd: YVO crystal as the solid-state laser crystal 15-1 having a thickness of 1 mm, and is integrally coupled with this.

Four

The converted wavelength conversion crystal 15-2 is composed of, for example, a KTP crystal that is a wavelength conversion crystal having a length of 3 mm. Here, the diameter of the ball lens 13 is 1.5 mm, and the laser from the semiconductor laser 12 is configured to excite the solid-state laser medium 15 via the ball lens 13 and output green laser light.

[0025] Solid laser crystal (Nd: YVO crystal) 15-1 and wavelength conversion crystal (KTP crystal) 15-2

Four

In order to join together, they can be joined together by bonding them with an epoxy adhesive, or they can be joined together by an optical contact method in which reinforcing glass is attached to the side surfaces of the two so that they are in contact with each other.

[0026] As the epoxy adhesive, a highly transparent epoxy adhesive, which is desired, is commercially available from a plurality of manufacturers, and may be appropriately selected and used. By the way, a large Nd: YVO crystal and KTP crystal of the order of cm can be easily aligned.

Four

After bonding with a highly transparent epoxy adhesive, a crystal with a desired size can be obtained by cutting to a few _mm . [0027] In the optical contact method, since bonding is performed without using an adhesive between the two, light absorption at the bonding surface can be suppressed to a low level. However, in terms of smoothness and adhesion of the bonding surface, It is a matter of course that very high accuracy is required!

[0028] The Nd: YVO crystal used as the solid-state laser crystal in this example is currently a semiconductor laser.

Four

It is one of the most efficient crystals for the pumped solid-state laser, has a high absorption coefficient at the excitation wavelength where the induced cross section at the laser oscillation wavelength is large, and a wider absorption bandwidth. Nd: YVO crystals have high power, high stability, and cost-effectiveness because they have excellent physical, optical, and mechanical properties that can be achieved with high damage thresholds due to laser light.

Four

It is an excellent crystal for semiconductor laser pumped solid state lasers.

[0029] In FIG. 1, the solid-state laser crystal (Nd: YVO crystal) 15-1 in the laser resonator and this

Four

A wavelength conversion crystal (KTP crystal) 15-2, which is integrated with this, is attached to the upper surface of the Peltier temperature control element 16. The temperature control device 17 connected to the Peltier temperature control element 16 has a built-in controller. The temperature sensor (thermistor, etc.) 18 attached to the Peltier temperature control element 16 is used in accordance with temperature data input from the temperature sensor 17. Temperature can be controlled.

[0030] The temperature of the Peltier temperature control element 16 is not optimally controlled by the temperature control device 17 but is controlled at an optimum temperature at which the laser output of the solid laser medium 15 becomes a predetermined value. It is. Such temperature control of the solid-state laser medium 15 has never been performed conventionally.

In order to control the temperature so that the laser output of the solid-state laser medium 15 becomes a predetermined value, the temperature change data of the solid-state laser medium 15 is collected by the temperature sensor 18 or the like, and the temperature change and laser output are collected. It is necessary to analyze the relationship between the temperature and the optimum temperature. The obtained value of the optimum temperature is fed back to the controller, and the temperature of the Peltier temperature control element 16 is controlled according to the temperature change of the solid-state laser medium 15. Thereby, the temperature can be controlled so that the laser output of the solid-state laser medium 15 becomes a predetermined value.

[0032] The green solid-state laser device shown in Fig. 1 has a solid-state laser crystal (Nd: YVO crystal).

Four

And a means for optimizing the positional relationship between the solid-state laser medium 15 composed of a wavelength conversion crystal (KTP crystal) 15-2 integrated with this and the pumping laser beam emitted from the pumping semiconductor laser device 11 It has. As a powerful optimization means, the excitation semiconductor layer It is preferable that the first device 11 and the solid-state laser medium 15 are guided and slid by a rail disposed on a pedestal. In addition, it is preferable that both are fixed in a large and small lens barrel and connected to each other so that they can slide and extend.

A selective reflection film 21 made of an dielectric multilayer film is formed on one end face that intersects the optical axis of the solid-state laser medium 15, that is, on the left end face in the drawing. This selective reflection film 21 is 99.99 nm for the fundamental wavelength laser light (L = 1064 nm) generated by the solid-state laser medium 15.

1

It has a high reflectance of 9% or more, while transmitting excitation laser light (L = 808nm) more than 90%.

0

It has the property to have. The other end face of the solid-state laser medium 15, that is, the right end face in the figure is not shown, but a non-reflective coating is applied to the green laser light L.

2

The reflectance for the laser light L of the fundamental wavelength at the end face is also 99% or more.

1

The laser beam L emitted from the solid state laser medium 15 is detected by a detector 22.

2

Output intensity and stability are detected. The laser beam L emitted from the solid-state laser medium 15 is a beam beam installed at an angle of about 45 degrees between the solid-state laser medium 15 and the detector 22.

2

It is bent 90 degrees by the presetter 23, and the Fabry-Perot scanning interferometer 24 checks whether the force is in the single longitudinal mode. Then, the data obtained by the detector 22 and the interferometer 24 are fed back to the temperature control device 17, and the temperature of the Peltier temperature control element 16 is controlled to the optimum temperature using the temperature control device 17.

The pumping semiconductor laser device 11 is a Ga As semiconductor laser having a center wavelength of oscillation of 808 nm and an output of 120 mW. Although not shown, in this embodiment, the semiconductor laser device 11 is provided with a temperature control device that maintains its temperature at 25 ° C., and the oscillation wavelength matches the absorption peak of the solid-state laser medium 15 described below. Yes It is set to 808nm.

The ball lens 13 condenses the excitation laser beam L emitted from the excitation semiconductor laser device 11 to collect the solid-state laser beam from the end surface on which the selective reflection film 21 of the solid-state laser medium 15 is formed.

0

The light enters the medium 15 and is excited. By utilizing the large aberration at the focal point of the ball lens, the excitation light can be efficiently converged in the solid-state laser crystal. [0037] The wavelength conversion crystal 15-2 is a Type II KTP crystal having a length of 3 mm. This KTP crystal is cut so that the crystal cut plane is Θ = 90.0 ° and φ = 23 °. Here, φ is the angle that the optical axis makes with the crystal Z axis, and Θ is the angle that the projection of the optical axis onto the crystal XY plane makes with the X axis, which is a condition that satisfies phase matching at room temperature. This allows solids using Nd: YVO crystals

Four

The laser beam L of 1064nm generated by the laser crystal 15-1 is incident and the wavelength of 532nm

1

Green light L is generated.

2

In the above-described configuration, the excitation laser light L emitted from the excitation semiconductor laser device 11 is condensed by the ball lens 13 and is incident on the solid laser medium 15 to be solid.

0

The laser medium 15 is excited. From this, a laser beam L having a fundamental wavelength is generated from the solid-state laser medium 15, and this laser beam L having a fundamental wavelength is generated by a solid-state laser crystal in the laser resonator.

1 1

Closed in (Nd: YVO crystal) and wavelength conversion crystal (KTP crystal) combined with this

Four

It can be filled. This confined fundamental wavelength laser beam L is converted into a wavelength conversion crystal (KTP crystal).

1

Through the second harmonic generation (SHG), which is a second-order nonlinear optical effect.

2 is generated. The green light L generated in this way is extracted outside as green laser light.

2

Is done.

FIG. 2 is a graph showing the time distribution of the output power of the green solid laser light at different laser operating temperatures. The vertical axis is output in arbitrary units (power), and the horizontal axis is time. The condition of this experiment is that the injection current to the semiconductor laser is 140-160mA, Nd: YVO crystal

The thickness of 4 is lmm, the thickness of the KTP crystal is 3mm, and the diameter of the ball lens is 1.5mm. Nd: YVO crystal and KTP crystal are bonded with an adhesive.

Four

[0040] As shown in Fig. 2, the operating temperature of the laser is 7.5 ° C (Fig. 2 (a)), 10 ° C (Fig. 2 (b)), 15 ° C (Fig. 2 (e)) and 17 At 5 ° C (Fig. 2 (f)), the output of the green solid-state laser fluctuates periodically, and the shape of the time variation of the output power varies with temperature. However, when the laser operating temperature reaches 12 ° C (Fig. 2 (c)) and 14 ° C (Fig. 2 (d)), the output power of the green solid-state laser becomes stable. Under the conditions where the laser operating temperature is 14 ° C and the pumping power of the semiconductor laser is 120 mW, a green solid laser with a maximum of 15.4 mW can be obtained.

From these results, by optimizing the operating temperature of the laser, not only the effect of keeping the temperature of the laser resonator as in the conventional case, but also the green noise that is an unstable factor of the laser output. It was shown that the problem can be solved.

[0042] When a laser oscillation experiment was performed with the green solid-state laser device under the above-described conditions, a graph of laser output as shown in Fig. 3 was obtained. As shown in Fig. 3, when the vertical axis is the output (power) and the horizontal axis is the time, the oscillation output is about 6 a.u. (arbitrary unit) and the laser output fluctuation is 0. An extremely stable green laser beam of 5% or less was obtained.

FIG. 4 is a graph showing the single longitudinal mode. As shown in Fig. 4, when the vertical axis is the output signal (FP signal) of the Fabry-Perot interferometer and the horizontal axis is the scanning time, the oscillation of the stable green laser light in single longitudinal mode is observed. It became possible to realize.

[0044] Based on Japanese Patent Application No. 2005-227312 filed on August 4, 2005. This content [all included here.

Industrial applicability

The green solid-state laser device of the present invention can be widely applied in the fields of processing, material process, spectroscopy, wafer inspection, light diagnosis, medical diagnosis, laser printing, and other information processing and optical measurement. There is industrial applicability.

Claims

The scope of the claims

[1] An excitation laser beam is incident on a first solid-state laser medium disposed in a laser resonator to oscillate a laser fundamental wave, and the laser fundamental wave is disposed in a second cavity disposed in the laser resonator. In an oscillation method of green solid laser light that is incident on a solid laser medium and oscillates green solid laser light,

Controlling the temperature of the first solid-state laser medium so that the laser fundamental wave oscillates in a single longitudinal mode, and the second solid-state laser medium so that the oscillation efficiency of the green solid-state laser light is maximized. A method for oscillating green solid-state laser light, characterized by controlling the temperature of the laser.

[2] The control temperature of the second solid-state laser medium is set so that the oscillation efficiency of the green solid-state laser light is within the temperature range of the first solid-state laser medium in which the laser fundamental wave is oscillated in a single longitudinal mode. 2. The method for oscillating green solid laser light according to claim 1, wherein the temperature is a maximum temperature.

[3] The green solid-state laser light according to claim 1 or 2, wherein the temperature control is performed by dividing a Peltier temperature control element into a plurality of unit surfaces so that the temperature can be controlled for each unit surface. Oscillation method.

[4] An excitation laser light source, a first solid-state laser medium that is disposed in a resonator and receives laser light from the excitation laser light source and oscillates a fundamental laser, and the basic laser beam that is disposed in the resonator A green solid-state laser oscillation device including a second solid-state laser medium that receives a wave laser beam and oscillates a green solid-state laser beam,

First temperature control means for controlling the temperature of the first solid-state laser medium so that the fundamental laser beam is in a single longitudinal mode;

A green solid-state laser oscillation device, comprising: a second temperature control means for controlling the temperature of the second solid-state laser medium so that the oscillation of the green solid-state laser beam has maximum efficiency.

[5] An excitation laser light source, a first solid-state laser medium that is disposed in the resonator and receives laser light from the excitation laser light source and oscillates a fundamental laser, and the basic laser medium that is disposed in the resonator Second solid-state laser medium that receives a wave laser beam and oscillates a green solid-state laser In a green solid state laser oscillation device including

The temperature of the first solid-state laser medium is controlled so that the fundamental laser light oscillated by the first solid-state laser medium is in a single longitudinal mode, and the green solid-state laser light is within the temperature range. And a temperature control means for controlling the temperature of the second solid-state laser medium so as to maximize the oscillation of the green solid-state laser oscillation device.

5. The green solid state laser oscillation device according to claim 4, wherein the temperature control means is a means capable of dividing the Peltier temperature control element into a plurality of unit surfaces and controlling the temperature for each unit surface.