JPH06273815A - Higher harmonic generator - Google Patents

Abstract

PURPOSE:To obtain stable output with simple constitution by forming the whole of higher harmonic generator by placing it on a pedestal consisting of material with specific linear expansion coefficient. CONSTITUTION:A second higher harmonic generator 9 is constituted by arranging an LD 2 as a laser beam source, a collimator lens 3, a mode matching lens 4, and a monolithic ring type resonator 5 on a base (pedestal) 6 of super- Invar material sequentially. Also, the holder (holding tool) of each element is manufactured by using the super-Invar material. The whole higher harmonic generator 9 is formed by placing on the pedestal 6 consisting of the material with linear expansion coefficient <=1.2X10<-6>. Also, the light source 2 of a fundamental wave, the collimator lens 3, and the mode matching lens 4 are formed to be holding with the holding tool consisting of the material with linear expansion coefficient <=1.2X10<-6>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a harmonic generator for converting a fundamental wave emitted from a laser light source into a harmonic in a resonator.

[0002]

2. Description of the Related Art In recent years, various devices have been proposed for obtaining a second harmonic wave or a third harmonic wave whose wavelength is converted by passing a fundamental wave emitted from a semiconductor laser or the like through a nonlinear optical material. In these devices, a nonlinear optical material is arranged in a resonator composed of a plurality of reflecting surfaces, and a fundamental wave is confined in the resonator to be amplified so that harmonics are efficiently generated.

As a resonator, a reflecting film is provided on the end face of a non-linear optical material, and a monolithic resonator for resonating inside the reflecting film and a plurality of mirrors are arranged to form the resonator. An external resonator in which a non-linear optical material is arranged is known. Recently, in order to downsize the device and improve the conversion efficiency to higher harmonics, the mainstream is shifting from the external resonator type to the monolithic type that resonates the fundamental wave inside the nonlinear optical material. I am doing it.

FIG. 2 shows, as an example of a conventional harmonic generator, a second harmonic generator using a monolithic ring type resonator.

This second harmonic generator 20 includes a semiconductor laser (hereinafter referred to as LD) 21, a collimator lens 22,
It is composed of a mode matching lens 23 and a non-linear optical material 24 made of KNbO ₃ crystal or the like. LD
21 emits a fundamental wave 25 having a wavelength of 860 nm, for example.

The left and right surfaces of the nonlinear optical material 24 in the figure are processed into spherical shapes. Of these, the surface on the left side of the drawing is the incident surface of the fundamental wave 25, and a spherical mirror 27 that partially transmits the fundamental wave 25 and reflects the second harmonic 26 is formed on this surface. The surface on the right side of the figure is the second harmonic 26
Is formed, and a spherical mirror 28 that reflects the fundamental wave 25 and transmits the second harmonic 26 is formed on this surface. Further, the lower surface of the nonlinear optical material 24 in the drawing forms a plane mirror 29 that reflects both the fundamental wave 25 and the second harmonic wave 26.

In the above structure, the fundamental wave 25 having a wavelength of 860 nm emitted from the LD 21 is collimated by the collimator lens 2.
The light is collimated by 2 and reflected by the mirror 30 attached to the PZT 31 and then passes through the mode matching lens 23 and enters from the point A of the spherical mirror 27 of the nonlinear optical material 24. At this time, the fundamental wave 25 is incident on the crystal axis a at a specific angle θ so that the fundamental wave 25 incident on the point A travels in parallel with the crystal axis a of the nonlinear optical material 24.

This fundamental wave 25 is generated by the two spherical mirrors 2
The light is reflected and amplified in a ring shape at points A, B, and C in the ring resonator constituted by 7, 28 and the plane mirror 29.
Then, the fundamental wave 25 passes through the crystal axis a in the nonlinear optical material 24.
When passing in the direction of, a part of the light is converted into the second harmonic wave 26 having a wavelength of 430 nm and emitted from the point B of the spherical mirror 28.

The nonlinear optical material 24 is temperature-controlled by a Peltier element or the like in order to meet the phase matching condition and stabilize the conversion efficiency to higher harmonics. Mirror 30
Is finely moved by the PZT 31 in order to adjust the optical path length so that the LD and the ring resonator form a composite resonator. In particular, since the optical path length between the LD and the ring resonator changes due to the thermal expansion due to the change of the temperature environment, the PZT 31 is adjusted so that the second harmonic output is monitored and the output becomes constant in order to cancel it. By using such a harmonic generator, the fundamental wave can be efficiently converted into a harmonic.

[0010]

However, the above conventional method has the following problems. The mechanism for adjusting the PZT 31 is shown in FIG. The second harmonic output is monitored by the photodiode 32, a drive signal is generated by the AC power supply 33, the lock-in amplifier 34, and the PI controller 35, and the PZT driver 36 drives the PZT. As described above, many devices are required to suppress the adverse effects such as the change of the optical path length and the change of the resonance condition, and the second harmonic generation device becomes large, complicated and expensive.

[0011]

In order to solve the above problems, the present invention provides a fundamental wave light source, a nonlinear optical material as a monolithic resonator, and a light source disposed between the light source and the nonlinear optical material. A harmonic generator comprising a coupling optical system, characterized in that the entire harmonic generator is mounted on a base made of a material having a linear expansion coefficient of 1.2 × 10 ⁻⁶ or less. A harmonic generation device is provided.

In a preferred embodiment of the present invention, each of the fundamental wave light source, the nonlinear optical material, and the coupling optical system is a holder made of a material having a linear expansion coefficient of 1.2 × 10 ⁻⁶ or less. The present invention provides a held harmonic generator.

Examples of the material having a linear expansion coefficient of 1.2 × 10 ⁻⁶ or less include invariant steel such as Invar (trademark) and Super Invar (trademark), Zerodur glass (trade name, manufactured by Shot Co., Ltd.). 2) and the like can be used, and these are preferable because they are less susceptible to changes in thermal expansion and thermal contraction, and thus the optical path length is also less likely to change.

In the present invention, the low thermal expansion material is
The linear expansion coefficient is 1. in the temperature range where the harmonic generator is used.
It may be 2 × 10 ⁻⁶ or less, and usually 50 ° C. or less so as to satisfy the above range. When the linear expansion coefficient has anisotropy, it is desirable that the linear expansion coefficient in any direction is 1.2 × 10 ⁻⁶ or less.

[0015]

[Function] The coefficient of linear expansion of Super Invar is 0.1 × 10
^Since it is ^-6 , the optical path length between the LD and the ring resonator is 20.
mm, when the temperature change is 30 ° C, the change in optical path length is 0.0
Since it is only 6 μm and the composite resonance condition of the LD and the ring resonator does not change, a stable second harmonic output can be obtained.

[0016]

FIG. 1 shows an embodiment in which the present invention is applied to a second harmonic generation device. The present invention is not limited to the second harmonic generation device, but can be applied to the third harmonic generation device and the like.

In the second harmonic generator 9, an LD 2 as a laser light source, a collimator lens 3, a mode matching lens 4, and a monolithic ring resonator 5 are mounted on a base (base) 6 made of Super Invar (trademark) material. It is arranged in order. Also, a holder for each element
Was also manufactured using Super Invar material. In this embodiment, the LD2 has a wavelength of 860 nm, a single longitudinal mode and a single transverse mode.
A device that emits a fundamental wave with little astigmatism is used.

[0018]

As described above, according to the present invention, it is possible to manufacture a harmonic generator having a stable structure and a stable output.

[Brief description of drawings]

FIG. 1 is a side view showing an embodiment of a harmonic generator of the present invention.

FIG. 2 is a side view showing an example of a conventional harmonic generator.

FIG. 3 is a side view showing an example of a conventional harmonic generator.

[Explanation of symbols]

 2, 21: Semiconductor laser (LD) 3, 22: Collimating lens 4, 23: Mode matching lens 5: Monolithic ring resonator 6: Base (base) 7, 8: Peltier element 9, 20: Second harmonic generation Device 24: Nonlinear optical material 25: Fundamental wave 26: Second harmonic 27, 28: Spherical mirror 29: Plane mirror 30: Mirror 31: PZT 32: Photodiode 33: AC power supply 34: Lock-in amplifier 35: P-I Controller 36: PZT driver 37: Half mirror

Claims (2)

[Claims] 1. A harmonic generator comprising a light source for a fundamental wave, a nonlinear optical material as a monolithic resonator, and a coupling optical system arranged between the light source and the nonlinear optical material. The linear expansion coefficient of the entire wave generator is 1.
A harmonic generation device characterized by being mounted on a base made of a material of 2 × 10 ⁻⁶ or less. 2. The light source for the fundamental wave, the non-linear optical material, and each component of the coupling optical system are held by a holder made of a material having a linear expansion coefficient of 1.2 × 10 ⁻⁶ or less. Harmonic generator.