JP2003174222A - Laser device - Google Patents

Abstract

(57) Abstract: Provided is a laser device capable of easily wavelength-matching a quasi-phase-matched wavelength conversion element having small temperature dependence by a temperature control system. A solid-state laser crystal is excited by excitation light from a semiconductor laser to generate a fundamental wave, and an output mirror is generated.
Oscillates in a resonator constituted by the surface 6a of the solid-state laser crystal 3 and the surface 3a of the solid-state laser crystal 3. Spiral coil rotating unit 1 attached to holder 8 and temperature-controlled by Peltier element 10
6, the quasi phase matching wavelength conversion element 4a provided in the resonator is rotated, the laser beam incident angle is changed, and wavelength conversion between the conversion center wavelength of the quasi phase matching wavelength conversion element and the resonator wavelength is performed. , And oscillates the second harmonic. The output is fed back to perform stable conversion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser device, and more particularly to a laser medium excited by a semiconductor laser,
The present invention relates to a laser device which oscillates a second harmonic by a non-linear optical crystal provided in a resonator.

[0002]

2. Description of the Related Art A method of using a semiconductor laser (LD) as an excitation light source has become widespread as a method of realizing high efficiency of a solid-state laser. By using the LD, it is possible to efficiently excite the absorption peak of the solid-state laser crystal,
Further, since the current-light output efficiency of the LD itself is high, there is an advantage that extra energy is not required. A semiconductor laser (LD) pumped solid-state laser device is widely used not only for research but also industrially because of its features such as low power, small size, long life, and easy handling.

FIG. 5 shows a conventional LD pumped solid state laser device. Here, in order to realize a blue laser, a semiconductor laser 1 (LD) and Nd: YAG as a solid-state laser crystal 3 are used.
KNbO ₃ as a crystal, a nonlinear optical crystal 4 for wavelength conversion
An LD pumped solid state laser device using a (KN) crystal will be described. In this device, the excitation light (809 nm) output from the semiconductor laser 1 passes through the lens 2 and is focused on the solid-state laser crystal 3 (Nd: YAG crystal). The fundamental wave (946 nm) output by the solid-state laser crystal 3 (Nd: YAG crystal) is the fundamental wave (946 nm) on the concave surface of the surface 3a of the solid-state laser crystal 3 (Nd: YAG crystal) and the surface 6a of the output mirror 6. The laser is oscillated by being confined in a resonator formed by applying a high-reflection coating.

By inserting a nonlinear optical crystal 4 (KNbO ₃ (KN) crystal) for wavelength conversion into this resonator,
The fundamental wave (946 nm) is KNbO ₃ (K
N) Induce the second harmonic (473 nm) from the crystal. The output mirror 6 is coated on the surface 6a so as to reflect the fundamental wave (946 nm) and transmit the second harmonic (473 nm), and the KNbO ₃ (KN) crystal (nonlinear optical crystal) for wavelength conversion is used. 4) 2nd harmonic (473n
m) is transmitted through the output mirror 6 and output to the outside. Then, the etalon 5 is inserted to suppress the generation of noise such as output failure or mode hop caused by longitudinal mode competition when the second harmonic is generated in the resonator, and the oscillation longitudinal mode is a single wavelength. It has become.

As described above, the nonlinear optical crystal 4 (KNb
Research and development of visible light lasers with second harmonics using O ₃ (KN) crystal are actively conducted, and among them, there is a great demand for laser light with low noise output.
Normally, in the generation of the internal resonator type second harmonic, longitudinal mode competition, noise due to mode hopping, etc. occur.
As a simplest method for suppressing the occurrence, a method of inserting the etalon 5 into the resonator and unifying the oscillation longitudinal mode (single wavelength) has been tried for a long time.

When the etalon 5 is used by inserting it in the resonator, the solid laser crystal 3 (Nd: Y) is used in the thickness design.
It is necessary to consider the gain width of the AG crystal) and the longitudinal mode interval determined by the resonator. Optimized etalon 5
Is the etalon 5 so that its transmission peak position does not move.
Temperature is kept constant. However, even if the temperature of only the etalon 5 is adjusted, the environmental temperature change in which the laser resonator is placed, the optical element used in the laser resonator, or the like causes excitation light or laser light that causes laser oscillation (basic (Wave) causes a temperature change in some way, and the effective resonator length changes. This change in the effective resonator length means a shift in the laser oscillation wavelength, and if the laser oscillation wavelength changes,
Since it moves to the transmission peak position of the etalon 5, the transmission peak of the etalon 5 that keeps the temperature constant and the laser oscillation wavelength deviate from each other, and stable laser oscillation with low noise cannot be performed. In case of mode hop or noise occurs.

Therefore, as shown in FIG. 5, the holder 7 and the holder 8 are fixed to a reference plate (not shown) so as to form an integrated resonator, and the semiconductor laser 1 and the lens 2 are attached to the holder 7.
And the solid-state laser crystal 3 (Nd: YAG
Crystal), nonlinear optical crystal 4 (KNbO ₃ (KN) crystal),
A method in which the etalon 5 and the output mirror 6 are adhered to each other, and the heat generated in the excitation section and the resonance section is cooled by the Peltier element 9 and the Peltier element 10 of the electronic cooling element through the holder 7 and the holder 8 and then dissipated by the heat sink. Is used.

Further, in order to stabilize the laser output, a feedback circuit mechanism is provided outside the laser resonator. A part of the laser light output from the output mirror 6 side is reflected by the splitter 11 and captured by the detector 12, the signal thereof is input to the comparator 13 and compared with the set value, and the control signal according to the increase / decrease is generated by the semiconductor. Laser 1 drive controller 14
And is fed back to the temperature controller 15. The output of the semiconductor laser 1 is controlled, and the temperature controller 15
The temperature of the optical element is controlled by the optical element, the effective length of the resonator is adjusted, the shift of the resonance wavelength is suppressed, and the laser output is stabilized.

[0009]

The conventional laser device is constructed as described above, and the KNbO ₃ used is used.
If it is a nonlinear optical crystal 4 such as (KN) crystal or KTP,
Since the wavelength of the peak of the conversion efficiency that generates a half wavelength greatly depends on the temperature, the temperature control of the Peltier element 10 controls the temperature at which the maximum conversion efficiency is obtained with respect to the oscillation wavelength of the resonator. As a result, the resonator wavelength and the conversion wavelength of the wavelength conversion element could be matched. But,
In general, QPM (Quasi-Phase-Match)
ing: Quasi-phase matching) Crystals such as lithium tantalate (LiTaO ₃ ) and lithium niobate (LiNbO ₃ ) which are materials for the wavelength conversion element have wavelengths conventionally used such as KNbO ₃ (KN) crystal and KTP. The temperature dependence of the central wavelength is smaller than that of the conversion element, and the conventional temperature control method using the Peltier element 10 has a problem that wavelength matching cannot be achieved.

On the other hand, the conversion efficiency g (λ) with respect to the wavelength (λ) of the QPM has the characteristics shown in FIG. 6, and the half width of the conversion center wavelength is only about 0.8 nm. It is necessary to match the resonance wavelength of the resonator. QPM
The conversion center wavelength of 1 depends on the QPM inversion period, and although the design is made based on the QPM domain inversion period, strict accuracy is required for the period. In order to manufacture the QPM wavelength conversion element so that the inversion period is exactly matched with the resonator wavelength, it is necessary to control the period on the order of nanometers, which is extremely difficult to manufacture.

The present invention has been made in view of such circumstances, and the temperature dependence of the conversion center wavelength is small,
An object of the present invention is to provide a laser device that can easily perform wavelength matching of a QPM wavelength conversion element that requires manufacturing precision for phase matching by a temperature control system such as a Peltier element.

[0012]

In order to achieve the above object, the laser device of the present invention has a quasi phase provided in a resonator by a laser beam of a fundamental wave oscillated by exciting a laser medium by the pumping light. In a laser device that oscillates a second harmonic by a non-linear optical effect of a matching wavelength conversion element, an angle between a laser light incident angle and a period direction of the quasi phase matching wavelength conversion element is changed by thermal expansion / contraction by temperature control. Rotation means is provided so as to match the oscillation wavelength of the resonator with the conversion center wavelength of the quasi phase matching wavelength conversion element.

The laser device of the present invention is characterized in that the rotating means has a spiral coil. The laser device of the present invention is characterized in that the rotating means has two angle adjusting rods having a large coefficient of thermal expansion.

The laser device of the present invention is configured as described above, and uses the semiconductor laser as the excitation light source, and the excitation light excites the solid laser crystal of the laser medium through the lens to oscillate the fundamental wave laser. The light causes laser oscillation of the second harmonic by the nonlinear optical crystal of the quasi phase matching wavelength conversion element provided in the resonator. Then, a rotation means that rotates by thermal expansion-contraction by temperature control, for example, a mechanism in which a spiral coil thermally expands-contracts and rotates depending on temperature, is provided to rotate the nonlinear optical crystal of the quasi-phase matching wavelength conversion element. The lasing wavelength of the quasi-phase matching wavelength conversion element changes with respect to the incident laser light, and the oscillation wavelength of the resonator matches the conversion center wavelength of the quasi-phase matching wavelength conversion element. Has been done.

As a result, a temperature control system using a Peltier element or the like can be used by using a QPM wavelength conversion element that has a small temperature dependence of the conversion center wavelength and requires the manufacturing accuracy of the wavelength conversion element for phase matching. The central wavelength of conversion of the QPM wavelength conversion element can be controlled to achieve wavelength matching, and stable laser output can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of a laser device of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG. 1 is a view showing a cross section of a laser device obtained by exciting a semiconductor laser 1 of the laser device of the present invention. FIG. 2 shows that the laser light of the laser device of the present invention is a quasi phase matching wavelength conversion element 4a (hereinafter,
It is shown that the inversion layer period Δ changes by changing the angle of incidence on the QPM wavelength conversion element 4a). FIG. 3 shows the QPM wavelength conversion element 4 of the laser device of the present invention.
It is a figure which shows the mechanism which rotates a.

This laser device is a semiconductor laser 1 which outputs excitation light (809 nm), a lens 2 which collects the excitation light on an end face of a solid-state laser crystal 3 provided in a resonator, and is excited by the excitation light. A solid-state laser crystal 3 having a surface 3a forming one end of a resonator and oscillating a laser (for example, a fundamental wave for blue: Nd: YAG crystal for 946 nm oscillation,
Fundamental wave for green: Nd: Y for 1064nm oscillation
VO ₄ crystal or the like), an output mirror 6 having a surface 6a forming one end of the resonator, an etalon 5 provided in the resonator for converting an oscillation longitudinal mode into a single wavelength, and a spiral coil rotating unit 1.
QPM wavelength conversion element 4a (for example, lithium tantalate (LiTaO ₃ ) crystal or lithium niobate (LiNbO ₃ ) crystal) for wavelength conversion, which is attached to No. 6 and generates a second harmonic by a nonlinear optical effect, and a laser. A spiral coil rotating part 16 for changing the angle between the light incident angle and the periodic direction of the QPM wavelength conversion element 4a by thermal expansion / contraction by temperature control, a solid-state laser crystal 3, a spiral coil rotating part 16, an etalon 5, and an output mirror 6. A holder 8 equipped with an optical element such as, and equipped with a cooling Peltier element 10,
A holder 7 equipped with a semiconductor laser 1 and a lens 2 and equipped with a Peltier element 9 for cooling, a detector 12 for capturing and detecting a part of laser output light with a splitter 11, and a signal from the detector 12 as set values. A comparator 13 that outputs a signal to be compared and increased / decreased and fed back, and a drive controller 14 that controls the driving of the semiconductor laser 1 by the signal from the comparator 13.
And the signal from the comparator 13 causes the Peltier elements 9, 10
And a temperature controller 15 for controlling.

The laser device of the present invention is different from the conventional device in that the wavelength conversion element of the nonlinear optical crystal 4 for generating the second harmonic in FIG. Therefore, the QPM wavelength conversion element 4a, which requires the manufacturing accuracy of the wavelength conversion element, is used. The QPM wavelength conversion element 4a is attached to the spiral coil rotating portion 16, and the spiral coil rotating portion 16 is connected to the Peltier element 10.
When the laser beam is rotated by thermal expansion and contraction under the temperature control by, the rotation angle θ between the laser light incident direction and the period direction of the QPM wavelength conversion element 4a is changed, the inversion layer period is changed, and the oscillation wavelength of the resonator is changed. This is because the QPM wavelength conversion element 4a can be matched with the conversion center wavelength.

FIG. 2A shows a state in which the laser light is incident in the same direction as the inversion layer periodic direction of the QPM wavelength conversion element 4a. The inversion layer period at this time is Δ, and as shown in (b), when the QPM wavelength conversion element 4a rotates by the rotation angle θ with respect to the laser light, the inversion layer period becomes Δcos θ. In this way, the QPM wavelength conversion element 4
When a is rotated, the inversion layer period changes with cos θ. This rotation is performed by the spiral coil rotating unit 16.

As shown in FIG. 3, the rotating mechanism (helical coil rotating portion 16) of the QPM wavelength converting element 4a includes a fixed base 16b attached to the holder 8 cooled by the Peltier device 10 and a fixed base 16b thereof. A rotary base 16a which is fitted in the bearing part and has the QPM wavelength conversion element 4a mounted on the upper part and which is freely rotatable horizontally. One end is fixed to the rotary base shaft 16e below the rotary base 16a and the other end is a fixing pin of the holder 8. The spiral coil 16c is fixed to 16d and is made of a metal material having a large thermal expansion coefficient. Since the spiral coil 16c has a spiral shape, it can be designed to have an appropriate length depending on the expansion coefficient of the metal used and the temperature control range of the Peltier element 10. And holder 8
Is cooled by the Peltier element 10, and by the cooler mechanism,
The spiral coil 16c expands and contracts, the generated rotational force is transmitted to the rotary base shaft 16e, the rotary base 16a rotates, and the attached QPM wavelength conversion element 4a rotates in the horizontal direction by a rotation angle θ according to the cooling temperature. .

Usually, the holder 8 and the holder 7, which are the base of the resonator of the laser device, are made of a material having a small expansion coefficient, and are made of a Peltier element 10 and a Peltier element 9 so as not to largely change with respect to changes in environmental temperature. For example, the temperature is kept constant. Similarly, the solid-state laser crystal 3,
Spiral coil rotating unit 16 (QPM wavelength conversion element 4a),
Optical elements such as the etalon 5 and the output mirror 6, the semiconductor laser 1 and the lens 2 are fixed to the holder 8 and the holder 7,
Not only the ambient temperature, but also expansion due to temperature changes due to the excitation light for laser oscillation and the fundamental wave once oscillated.
The effective resonator length changes due to the influence of the refractive index change, and the oscillation wavelength shifts.
Optical elements are attached so as to suppress or prevent wavelength shift due to temperature change. Then, through the holder 8, the entire resonator is controlled by the heat control including the heater and the cooler using the Peltier element 10 or the like so that the temperature becomes constant. In particular, the etalon 5 may be temperature-adjusted separately from other optical elements in order to suppress the fluctuation of the transmission peak position. Further, the spiral coil rotating unit 16 to which the QPM wavelength conversion element 4a is attached may be cooled by individual temperature adjustment.

Next, the operation of the laser device shown in FIG. 1 will be described. Excitation light (809 nm) output from the semiconductor laser 1 passes through the lens 2 and is focused on the solid-state laser crystal 3 (Nd: YAG crystal). The fundamental wave (94) output by the solid-state laser crystal 3 (Nd: YAG crystal)
6 nm) on the concave surface of the surface 3a of the solid-state laser crystal 3 (Nd: YAG crystal) and the surface 6a of the output mirror 6 (94 nm).
6 nm) is confined in a resonator constituted by applying a highly reflective coating, and laser oscillation occurs. A QPM wavelength conversion element 4a (LiT
aO ₃ crystal, LiNbO ₃ crystal, etc.) are fixed on the spiral coil rotating part 16 by an adhesive or the like and inserted into the laser beam, and the spiral coil rotating part 16 is connected to the Peltier element 10 via the holder 8 by the temperature controller 15. Temperature controlled.

Then, by controlling the temperature, the spiral coil 16c of the spiral coil rotating portion 16 expands and contracts, and the rotary table 16
a rotates, the QPM wavelength conversion element 4a rotates in the horizontal direction, the inversion layer period changes, the conversion center wavelength is controlled, and the oscillation wavelength of the resonator matches the conversion center wavelength in the QPM wavelength conversion element 4a. Therefore, the second harmonic (473 nm) is efficiently induced from the QPM wavelength conversion element 4a. The output mirror 6 reflects the fundamental wave (946 nm) and transmits the second harmonic wave (473 nm) on the surface 6a.
Coating on the QPM wavelength conversion element 4
The second harmonic wave (473 nm) from a is transmitted through the output mirror 6 and output to the outside. Then, the etalon 5 is inserted to suppress the generation of noise such as output failure or mode hop caused by longitudinal mode competition when the second harmonic is generated in the resonator, and the oscillation longitudinal mode is a single wavelength. It has become.

A feedback circuit mechanism is provided outside the laser resonator, a part of the laser light output from the output mirror 6 side is reflected by the splitter 11 and captured by the detector 12, and the signal thereof is sent to the comparator 13. The input signal is compared with the set value, and the control signal according to the increase / decrease is fed back to the drive controller 14 and the temperature controller 15 of the semiconductor laser 1. Then, the output of the semiconductor laser 1 is controlled, and the temperature controller 15 controls the temperature of the optical element and the spiral coil rotating unit 16 to match the oscillation wavelength of the resonator with the conversion center wavelength of the QPM wavelength conversion element 4a. The
Further, the effective length of the resonator is adjusted, the QPM wavelength conversion element 4a is always used with high conversion efficiency, and a stable laser output can be obtained even if the resonance wavelength of the resonator deviates with time. .

Next, another embodiment of this laser device will be described with reference to FIG.
Will be described with reference to. FIG. 4 shows a QPM wavelength conversion element 4
The figure which looked at a from the upper part is shown. Instead of the spiral coil rotating part 16 shown in FIG. 1, two ends of an angle adjusting rod 17 of two metal rods having a large thermal expansion coefficient are directly attached to the holder 8 at two diagonal corners and the other end of the QPM wavelength conversion element 4a. To the QPM wavelength conversion element 4a by thermally rotating the angle adjusting rod 17 by controlling the temperature by connecting a rotary joint mechanism (a mechanism in which the force can be transmitted in any direction to the angle adjusting rod 17). Is rotated horizontally about the rotation center 16f.

Conventionally, it was difficult to strictly match the conversion wavelength of the QPM wavelength conversion element 4a and the resonator wavelength,
The laser device of the present invention uses the heat control method of the Peltier elements 10 and 9 which has been conventionally used as it is,
QPM by controlling the angle of the QPM wavelength conversion element 4a
The conversion wavelength of the wavelength conversion element 4a and the resonator wavelength can be easily matched.

[0027]

The laser device of the present invention is configured as described above, and the nonlinear optical crystal of the quasi phase matching wavelength conversion element is provided in the resonator of the semiconductor laser pumped solid-state laser device, and the thermal expansion by temperature control is performed. -The rotation mechanism that rotates due to contraction rotates the quasi-phase matching wavelength conversion element, changes the angle with the period direction of the quasi-phase matching wavelength conversion element with respect to the incident laser light, and the oscillation wavelength of the resonator and the quasi-phase The second harmonic laser oscillates so as to match the conversion center wavelength of the matching wavelength conversion element. Therefore, a quasi-phase-matching wavelength conversion element, which requires high manufacturing accuracy and has a small temperature dependence of the conversion center wavelength, can be wavelength-matched by controlling with a conventional temperature control system such as a Peltier element, and a stable laser can be obtained. You can get the output.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a laser device of the present invention.

FIG. 2 is a diagram for explaining a change in inversion layer period of the quasi phase matching wavelength conversion element according to the embodiment of FIG.

FIG. 3 is a diagram showing a spiral coil rotating portion of the laser device of the present invention.

FIG. 4 is a diagram showing another embodiment of the laser device of the present invention.

FIG. 5 is a diagram showing a conventional laser device.

FIG. 6 is a diagram showing conversion efficiency characteristics with respect to wavelength of a quasi phase matching wavelength conversion element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser 2 ... Lens 3 ... Solid-state laser crystal 3a, 6a ... Surface 4 ... Nonlinear optical crystal 4a ... Quasi phase matching wavelength conversion element (QPM wavelength conversion element) 5 ... Etalon 6 ... Output mirror 7, 8 ... Holder 9, 10 ... Peltier element 11 ... Splitter 12 ... Detector 13 ... Comparator 14 ... Drive controller 15 ... Temperature controller 16 ... Helical coil rotating part 16a ... Rotating base 16b ... Fixed base 16c ... Helical coil 16d ... Fixed pin 16e ... Rotation Base shaft 16f ... Rotation center 17 ... Angle adjustment rod

Claims (3)

[Claims] 1. A laser device which oscillates a second harmonic by a nonlinear optical effect of a quasi phase matching wavelength conversion element provided in a resonator, by a laser light of a fundamental wave oscillated by exciting a laser medium by the excitation light. In, a rotation means for changing the angle between the laser light incident angle and the period direction of the quasi phase matching wavelength conversion element by thermal expansion-contraction by temperature control is provided, and the oscillation wavelength of the resonator and the quasi phase matching wavelength conversion element. A laser device characterized by being matched with the conversion center wavelength in. 2. The laser device according to claim 1, wherein the rotating means has a spiral coil. 3. The rotating means has two angle adjusting rods having a large coefficient of thermal expansion.
The laser device described.