JP2634312B2 - Phase conjugate mirror and laser resonator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a self-excitation type phase conjugate mirror and a laser resonator using the same.

[Conventional technology]

In a normal laser oscillator, the non-uniformity of the beam generated in the amplification medium is reflected and amplified by the laser resonator as it is, so that the liquid level of the output beam becomes non-uniform. On the other hand, in a system in which one mirror of the laser resonator is a self-excitation type phase conjugate mirror, the wavefront of the output beam becomes clean due to the phase distortion compensation of the phase conjugate.
Such a system is disclosed in, for example, Japanese Patent Publication No. 59-500888 (International Publication No. WO83 / 04144).

FIG. 4 shows a conventional system using a phase conjugate mirror. As shown, a normal reflection mirror 2 is provided on one side of an amplification medium 1 such as an argon gas, and a phase conjugate mirror 4 is provided on the other side with a lens 3 interposed therebetween. Here, as the phase conjugate mirror 4, for example, a BTO (BaTiO ₃ ) crystal or the like is used.

[Problems to be solved by the invention]

The reflectivity of the phase conjugate mirror 4 used in such a system is generally lower than that of a normal mirror, such as about 40%. Therefore, in order to obtain a high laser output, a medium having a large amplification factor is required as the amplification medium 1, which is not suitable for practical use.

Therefore, an object of the present invention is to provide a self-excitation type phase conjugate mirror having a high reflectance and a laser resonator capable of realizing a laser output having a clean wavefront with high efficiency.

[Means for solving the problem]

A self-excitation type phase conjugate mirror according to the present invention includes: an optical member made of an optical nonlinear medium; and a modulation unit that supplies energy for temporally modulating the refractive index of the nonlinear medium to the optical member. And

Further, a laser resonator according to the present invention is characterized in that the above-described phase conjugate mirror is used as one mirror of the laser resonator.

[Action]

According to the present invention, the refractive index of the optical non-linear medium is temporally modulated by the modulating means, so that the reflectivity of the medium increases and the reflectivity as a mirror improves. Therefore, when this phase conjugate mirror is used in a laser resonator, the efficiency of laser output is improved and the wavefront of laser output light is clear.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

Prior to the description of specific examples, a brief description of the circumstances leading to the completion of the present invention will be given in the literature by WB Whitten et al. (“OPTICS LETTERS / Vol.9, No.
According to P.44-46 "etc., in four-wave mixing used to generate a phase conjugate wave, one of the writing lights is slightly shifted in frequency, and the reflectance is improved by moving interference fringes on the crystal. In the self-excited phase conjugate optical system according to the present invention, it is considered that the reflectivity is increased because the signal light is passively subjected to the frequency shift in the crystal. It is difficult to control the effect, so the present invention relates to a method of controlling the reflectivity of a mirror in addition to a refractive index modulation to a nonlinear optical material, which is a phase conjugate mirror, from the outside in a self-phase conjugate mirror and a laser resonator having the same. It is to make it even larger and control it.

FIG. 1 is a configuration diagram of a phase conjugate mirror according to the first embodiment and a laser resonator using the same. As shown in the figure, in this embodiment, the phase conjugate mirror 4 includes a BTO crystal 41, electrodes 42a and 42b attached to both ends of the BTO crystal 41, and a voltage applied between them to apply an AC electric field to the BTO crystal 41. Power supply to be applied 43
And Here, the modulation means is configured to apply an external electric field to the BTO crystal 41, but may be configured to apply an ultrasonic compression wave as in a second embodiment described later.

In the laser device of FIG. 1 having such a phase conjugate mirror, laser oscillation starts and argon laser light is emitted.
When incident on the BTO crystal 41, B
The refractive index distribution is modulated in the crystal of the TO crystal 41. At this time, the light in the BTO crystal 41 undergoes frequency modulation of about 1 Hz or less, and the reflectance as a phase conjugate mirror increases due to the passive frequency shift. In addition, in the present embodiment, the electric field applied to the BTO crystal 41 from the power supply 43 via the electrodes 42a and 42b is time-modulated, and the refractive index is time-modulated in accordance with the electric field. The refractive index grating formed inside is time-modulated. As a result, it is possible to further increase the reflectance as compared with the above-described passive reflectance shift.

FIG. 2 shows a configuration of a phase conjugate mirror according to the second embodiment and a laser resonator using the same. In this embodiment, the phase conjugate mirror 4 has a BTO crystal 41, transducers 44a and 44b attached to both ends thereof for generating ultrasonic waves perpendicular to the C-axis, and a power supply 43 for driving these. According to this, the compression wave is generated by the ultrasonic wave in the BTO crystal 41, and the amplitude and the cycle of the ultrasonic wave are temporally changed. Then, the refractive index of the BTO crystal 41 is temporally modulated,
The refractive index grating formed there is changed over time. As a result, the reflectance as a phase conjugate mirror is improved.

In the laser device of the embodiment shown in FIG. 2, such a phase conjugate mirror is used as one of the mirrors to constitute a laser resonator, and a dye cell 11 such as rhodamine 6G is used as a laser medium. Then, the dye cell 11 is irradiated with an argon ion laser beam or the like as pump light to amplify fluorescence generated by excitation, thereby causing laser oscillation. This embodiment is characterized in that the oscillation spectrum of the dye cell 11 is narrowed and the oscillation wavelength is scanned without permission. Therefore, by temporally modulating the refractive index of the BTO crystal 41, not only can the power of the laser light output be improved, but also the wavelength and speed of scanning of narrow-band laser light can be controlled. For this reason,
Applications in the field of spectroscopy can be expected. Note that a similar laser device can be realized when a YAG crystal is used as a laser amplification medium.

FIG. 3 is a configuration diagram of a phase conjugate mirror according to a third embodiment and a laser resonator using the same. In this example,
Pump light whose intensity is represented by a function of time I (t) and whose frequency is also represented by a function of time f (t) is incident on the BTO crystal 41, thereby realizing the phase conjugate mirror 4. As described above, when the pump light whose intensity and frequency change over time is incident on the BTO crystal 41, the refractive index grating is modulated over time, and the reflectance as a phase conjugate mirror increases. Therefore, even when the laser device shown in FIG. 3 is configured using the phase conjugate mirror 4, high-power laser light having a clear wavefront can be obtained.

〔The invention's effect〕

As described above in detail, according to the present invention, the refractive index of the optical nonlinear medium is temporally modulated by the modulating means, so that the reflectivity of the medium increases and the reflectivity as a mirror improves. . Therefore, when this phase conjugate mirror is used for a laser resonator, there is an effect that the power efficiency of the laser output is improved and the wavefront of the laser output light is clear.

[Brief description of the drawings]

FIG. 1 shows a phase conjugate mirror according to a first embodiment of the present invention,
FIG. 2 is a diagram showing a configuration of a laser resonator using the same, FIG. 2 is a diagram showing a configuration of a phase conjugate mirror according to a second embodiment of the present invention and a laser resonator using the same, and FIG. The third
FIG. 4 is a diagram showing a configuration of a phase conjugate mirror according to an embodiment and a laser resonator using the same, and FIG. 4 is a diagram showing a configuration of a conventional phase conjugate mirror and a laser resonator using the same. 1 ... Amplifying medium, 2 ... Reflection mirror, 3 ... Lens, 4
… Phase conjugate mirror, 41… BTO crystal.

Claims (3)

(57) [Claims] An optical member comprising an optical nonlinear medium;
A self-excitation type phase conjugate mirror, comprising: a modulation unit that supplies energy for temporally modulating the refractive index of the nonlinear medium to the optical member. 2. The phase conjugate mirror according to claim 1, wherein the energy supplied to said optical member is a temporally modulated ultrasonic wave, electric field or light. 3. A laser resonator comprising a pair of mirrors provided with a laser amplifying medium interposed therebetween, wherein one of the pair of mirrors is an optical member made of an optical nonlinear medium and the refractive index of the nonlinear medium is time-dependent. A laser resonator comprising: a modulation unit that supplies energy to be optically modulated to the optical member.