JPH06164044A - Tunable laser apparatus - Google Patents

Abstract

PURPOSE:To provide a tunable laser apparatus wherein it utilizes an optical parametric oscillation and it can convert a wavelength up to a wider wavelength region. CONSTITUTION:A laser apparatus is constituted fundamentally of an excitation source 1, of a nonlinear optical element 2 for optical parametric oscillation and of one pair of reflectors 3 which are arranged on the incident side and the radiant side of the nonlinear optical element 2 for optical parametric oscillation use. In the laser apparatus, the nonlinear optical element 2 is constituted of a plurality of nonlinear optical elements 4 which have been cut out to be respectively prescribed orientations, of a crystal holder 5 which holds the optical elements 4 and of a shaft 6 which is used to turn the crystal holder 5, and it is constituted in such a way that the nonlinear optical elements 4 are situated in the light path of a laser beam resonated between the reflectors 3 when the holder 5 is turned. Thereby, when a plurality of crystals whose orientation is different are used as the nonlinear optical elements, a tunable region can be expanded easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical parametric oscillator using a nonlinear optical crystal, and more particularly to an optical parametric oscillator capable of varying the wavelength of laser light emitted by rotating the nonlinear optical crystal.

[0002]

2. Description of the Related Art 1 / λp = 1 / λs + 1 / λi (1) np / λp = ns / λs + ni / Λi (2) coherent light having different wavelengths (λs and λi, λs is a signal, λi is an idler, λs <λi,
Optical parametric oscillation for generating np, ns, and ni are known. This oscillator is generally composed of an excitation light source, a nonlinear optical element, and a pair of reflecting mirrors arranged on the incident side and the emission side of the nonlinear optical element. Then, the light emitted from the excitation light source resonates between the reflecting mirrors provided on both sides of the nonlinear optical element, the wavelength is converted, and the light is emitted. Conventionally, KTiOPO ₄ (KTP) and RbTiOPO ₄ (RTP) have been used for this kind of optical parametric oscillator.
A non-linear optical crystal such as 1.047-1.0 is used.
Nd: YLF, Nd: YAG, N oscillating at 796 μm
Solid-state lasers such as d: GSGG and Nd: YAP are often used as excitation light sources.

By the way, the laser light is characterized by a narrow wavelength distribution and good straightness, and its wavelength is specified by the material used. However, in recent years, there has been a demand for a laser device capable of oscillating laser light of various wavelengths from a single device while maintaining the narrow wavelength distribution and good straightness. For example, it is used for analysis of various components in the atmosphere. In addition, there is a case where a laser beam having a wavelength in a region that cannot be obtained with the current material is required, and a problem has arisen as to how to obtain such a laser beam.

Various studies have been made to meet such requirements and problems. One of the studies is KTP and RTP.
There is a method of changing the propagation angle of laser light in a nonlinear optical crystal in the optical parametric oscillator using the. This is because optical parametric oscillation using KTP or RTP is a-cut 90 ° phase matching (φ = 0 °, θ =
Around 90 °), the spectrum width is as narrow as several Angstroms, and according to this method, theoretically, the propagation angle of the laser beam is within the range of 40 to 90 degrees (the maximum variation of the propagation angle is 50 degrees). By changing the above wavelength 1.047 ~
Laser light of 1.0796 μm wavelength 1.08 to 3.3 μm
This is because the wavelength can be converted into the laser light in the range.

However, the size of a nonlinear optical crystal for optical parametric oscillation that is usually used is 5 × 5 × 10.
The range is about 20 mm, and the range in which the nonlinear optical crystal can be rotated is about 20 ° within a range in which the emitted light of sufficient intensity can be obtained, and it is difficult to perform sufficient wavelength conversion. Particularly in the vicinity of 90 ° phase matching, even if the element is rotated by 20 °, the wavelength of the laser light of 1.047 to 1.0796 μm can be converted to the wavelength of 1.622 to 1.652 μm.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a wavelength tunable laser device utilizing optical parametric oscillation and capable of wavelength conversion to a wider wavelength range.

[0007]

The apparatus of the present invention for solving the above-mentioned problems comprises an excitation light source (1), a nonlinear optical element for optical parametric oscillation (2), and a nonlinear optical element for optical parametric oscillation (2). In a laser device basically composed of a pair of reflecting mirrors (3) arranged on the entrance side and the exit side of the non-linear optical element (2), a plurality of non-linear optical elements (2) are cut so as to have a predetermined azimuth. A nonlinear optical element (4), a crystal holder (5) for holding the optical element (4), and a rotation shaft (6) for rotating the crystal holder (5), the holder (5) Is rotated so that the non-linear optical element (4) can be positioned in the optical path of the laser beam resonating between the reflecting mirrors (3).

[0008]

The laser device of the present invention is basically an optical parametric oscillator, and the advantages that the obtained laser light has a narrow wavelength distribution and good straightness are not lost. In the present invention, a plurality of nonlinear optical elements cut out so as to have a predetermined orientation are attached to a crystal holder, and the crystal holder is rotated to position the predetermined nonlinear optical element in the optical path of laser light resonating between reflecting mirrors. This is done in order to increase the amount of change in the propagation angle of the laser light and increase the conversion width of the laser term.

The present invention will be further described with reference to the drawings.
1 is a configuration diagram of one embodiment of a wavelength tunable laser device using optical parametric oscillation according to the present invention, and FIG. 2 is an external view of a nonlinear optical element for optical parametric oscillation used in FIG. This apparatus comprises an excitation light source (1) and a nonlinear optical element (2) for optical parametric oscillation, which is a feature of the present invention.
And a pair of reflecting mirrors (3) (rear mirror (7), output mirror (8)), and a nonlinear optical element (2) for optical parametric oscillation is provided as shown in FIG. The non-linear optical element (4) (4 '), the crystal holder (5), and the rotating shaft (6), and the rotating shaft (6)
The crystal holder is rotated around the center so that the predetermined nonlinear optical element (4) is positioned in the optical path of the laser beam resonating between the rear mirror (7) and the output mirror (8). Two non-linear optical elements (4) (4 ') in FIG.
Are two different azimuth type-2 ((θ = 6
5 °, φ = 0 °) and (85 °, φ = 0 °) cut KTP crystals (where φ and θ are z (= c) and x (=
a) Angle portion of polar coordinates measured from the axis).

In the apparatus of the present invention, the nonlinear optical element (4)
Even if the crystal holder is rotated about the rotation axis and replaced with another non-linear optical element (4 '), the wavelength can be tuned without changing the resonance state. The axial direction of and the axial direction of the rotating shaft (6) are aligned.

In this embodiment, the excitation light source (1) is
Although Nd: YAG was used and a KTP crystal was used as the nonlinear optical element, Nd: YLF, N was used as the other pumping light source.
A solid-state laser such as d: GSGG or Nd: YAP can be used, and RTP can be used as the nonlinear optical element.

The rear mirror (7) used in this embodiment is either signal light (wavelength shorter than twice the wavelength of the pump laser light) or idler light (wavelength longer than twice the wavelength of the pump laser light). The output mirror (8) is a dichroic mirror having a reflectance of 50-98% for either signal light or idler light.

In order to obtain a laser beam by the apparatus of this embodiment, for example, the wavelength of the excitation light source (1) is 1.064 μm.
Using the Nd: YAG laser oscillating at 1, the nonlinear optical element is rotated with respect to the laser optical axis together with the crystal holder (5) so that the nonlinear optical crystal (4) has a required output light wavelength. It is sufficient to adjust the incident angle of the laser light on the incident end face of. When the variable range of one nonlinear optical crystal (4) is exceeded, the rotation axis (6) in FIG.
The holder (5) is rotated by to replace the nonlinear optical crystal (4 ′). As a result, the wavelength variable range can be expanded.

[0014]

EXAMPLES Next, examples of the present invention will be described. (Example 1) Nd: YAG laser was used as a pumping light source, and a nonlinear optical element was cut out with θ = 68 °, φ = 0 °, and an optical path length of 10 mm, and formed. Using the RTP crystal obtained in the above, and the RTP crystal obtained by cutting and molding at θ = 85 °, φ = 0 ° and an optical path length of 10 mm, 1.6 to 1.
A device having the same configuration as the wavelength tunable laser device shown in FIG. 1 was constructed by using as the rear mirror and the output mirror those capable of resonating in the range of 8 μm, and optical parametric oscillation was performed using this device.

First, a crystal of θ = 85 ° was used, and this crystal was rotated so that the output did not fall below a predetermined value with respect to the optical axis, and the oscillation wavelength was measured. As a result, 1.622
It was possible to change the wavelength in the range of -1.68 μm. Next, the same oscillation experiment was conducted by replacing the crystal with θ = 68 °. As a result, it was possible to vary in the range of 1.66-1.8 μm. From this result, it was found that by using the device used in this example, the laser beam having the wavelength of 1.064 μm can be changed within the range of 1.622 to 1.8 μm without causing the output reduction.

[0016]

The wavelength tunable laser device of the present invention can easily widen the wavelength tunable range by using a plurality of crystals having different directions for the nonlinear optical element used.

[Brief description of drawings]

FIG. 1 is a configuration diagram of one embodiment of a wavelength tunable laser device using optical parametric oscillation according to the present invention.

FIG. 2 is an external view of a nonlinear optical element for optical parametric oscillation used in FIG.

[Explanation of symbols]

1 --- Excitation Light Source, 2 --- Nonlinear Optical Element for Optical Parametric Oscillation, 3 --- Reflecting Mirror, 4,4 '--- Nonlinear Optical Element, 5 --- Crystal Holder, 6 --- Rotation Axis , 7
--- Rear mirror, 8-- Output mirror

Claims (2)

[Claims] 1. A pumping light source (1), a nonlinear optical element for optical parametric oscillation (2), and a pair of reflecting mirrors arranged on the incident side and the emitting side of the nonlinear optical element for optical parametric oscillation (2). In a laser device basically composed of 3) and 3), a nonlinear optical element (2) for optical parametric oscillation is cut into a plurality of nonlinear optical elements (4) each having a predetermined azimuth, and the nonlinear optical element. It is composed of a crystal holder (5) for holding the element (4) and a rotation shaft (6) for rotating the crystal holder (5), and by rotating the holder (5), a nonlinear optical element (4) ) Is arranged in the optical path of the laser light resonating between the reflecting mirrors (3). 2. The wavelength tunable laser device according to claim 1, wherein the non-linear optical element (4) is either KTP or RTP.