JP2654728B2 - Optical wavelength converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical wavelength converter for shortening a wavelength of a laser beam, and more particularly, to generating a second harmonic by irradiating a laser beam on a crystal of a first nonlinear optical material. Further, the present invention relates to an optical wavelength converter for generating the sum frequency of the second harmonic and the laser beam by making the laser beam incident on a crystal of a second nonlinear optical material.

[0002]

2. Description of the Related Art As disclosed in, for example, Japanese Patent Application Laid-Open No. Sho 62-189783, a laser diode pumped solid laser in which a solid laser rod doped with a rare earth such as neodymium is pumped by a semiconductor laser (laser diode) is known. ing. In this type of solid-state laser, a bulk single crystal of a nonlinear optical material is disposed in the resonator to convert the solid-state laser oscillation beam into a second harmonic in order to obtain a laser beam having a shorter wavelength. Things have also been done.

Further, in order to obtain a laser beam having a shorter wavelength, for example, in an ultraviolet region, a technical digger has been developed.
est of Conference on Lasers and Electro-Opt
ics, 1991. As shown on page 218, attempts have been made to make a solid-state laser oscillation beam and its second harmonic incident on a crystal of a second nonlinear optical material to generate a sum frequency thereof. This optical wavelength conversion device, more specifically,
A YAG crystal, which is a solid laser medium, is pumped with lamp light to obtain a solid laser beam having a wavelength of 1064 nm. The solid laser beam is made incident on a KTP crystal, which is a first nonlinear optical material crystal, to produce a second harmonic having a wavelength of 532 nm. A second harmonic and the solid-state laser beam
Is incident on a BBO crystal as a non-linear optical material crystal to obtain a sum frequency having a wavelength of 355 nm.

In this type of optical wavelength converter, a crystal of a first nonlinear optical material is arranged in a resonator of a solid-state laser so that a solid-state laser beam is incident on the crystal in a state of resonance. If this is done, the solid-state laser beam will be incident on this crystal at a high output, which is advantageous in achieving high wavelength conversion efficiency. Similarly, it is preferable that the second harmonic generated from the crystal of the first nonlinear optical material is incident on the crystal of the second nonlinear optical material in a state of resonance. Therefore, in the above-mentioned conventional apparatus, the first resonator mirror of the first and second resonator mirrors for the solid-state laser is also used for the second harmonic, and the first resonator mirror is disposed between the resonator mirrors. A third resonator mirror for the second harmonic is arranged, and the first and second nonlinear optical material crystals are placed between the first and third resonator mirrors. The solid state laser beam is incident on the crystals of the first and second nonlinear optical materials, and the second resonating second harmonic is incident on the crystal of the second nonlinear optical material.

[0005]

This optical wavelength converter can obtain a laser beam of an extremely short wavelength, but has a very low wavelength conversion efficiency on the other hand. Therefore, only a pulsed laser beam capable of increasing the internal power was obtained, and a continuous operation laser beam having a low internal power was not obtained. As a specific example, when the output of a pumping lamp is set to 5 kW, a solid-state laser is oscillated by Q-switch, its internal power is increased, and phase matching of type I is performed between two fundamental waves and a sum frequency. Reported that the sum frequency output was 100 mW.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to obtain a laser beam of extremely short wavelength by continuous operation by generating a second harmonic and a sum frequency. It is an object of the present invention to provide an optical wavelength converter capable of realizing efficiency.

[0007]

According to the present invention, there is provided an optical wavelength conversion apparatus comprising: a first nonlinear optical material in which a laser beam obtained by pumping a solid laser medium is disposed in a solid laser resonator; Into the crystal of the second
In an optical wavelength conversion device for generating a harmonic, making this second harmonic and the laser beam incident on a crystal of a second nonlinear optical material, and generating a sum frequency thereof, one of solid-state laser resonators is formed. The mirror is also used as one mirror of the second harmonic resonator, the outer end face of the solid-state laser medium is coated with the other mirror of the solid-state laser resonator, and the inner end face of the solid-state laser medium is The second harmonic resonator is coated with a coating that serves as the other mirror of the second harmonic resonator.

[0008]

In the above configuration, the second
Since the higher harmonic wave is incident on the crystal of the second nonlinear optical material in a state of resonance, the second harmonic wave can be incident on the crystal with high output. In this configuration, since the resonator mirror for the second harmonic is not inserted in the resonator of the solid-state laser, loss due to the passage of the solid-state laser beam through the resonator mirror is eliminated, and high wavelength conversion is achieved. Efficiency is realized.

In the above configuration, the solid-state laser medium is used as the second harmonic resonator. However, since a coating for this is formed on the inner end face of the laser medium, the solid-state laser medium extends to the inside of the solid-state laser medium. The second harmonic rarely reaches. Therefore, the second harmonic is not absorbed by the solid-state laser medium, the temperature rises, and the efficiency of solid-state laser oscillation does not decrease.

Furthermore, in the above configuration, the number of parts is reduced because there is no resonator mirror dedicated to the second harmonic, and in addition, the adjustment of the resonator mirror does not occur. The performance is also improved.

As described above, the inner end face of the solid-state laser medium serving as the resonator mirror surface for the second harmonic needs to transmit the solid-state laser beam satisfactorily. Will be done. Here, it is generally easy to polish the solid-state laser medium in a state in which both end faces have extremely high parallelism (for example, an error of about 30 seconds or less). When the laser beam is adjusted so as to be vertically incident on its outer end face in order to resonate satisfactorily, this laser beam is naturally also vertically incident on the inner end face of the solid-state laser medium with high precision. Therefore, even if the characteristics of the anti-reflection coating are deteriorated, the reflection loss of the solid-state laser beam at the inner end face of the solid-state laser medium becomes almost negligibly low, and the wavelength conversion efficiency is also improved from this point. Become.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. FIG. 1 shows an optical wavelength converter according to a first embodiment of the present invention. This optical wavelength conversion device is, for example, incorporated in a laser diode pumped solid-state laser. The laser diode pumped solid-state laser includes a semiconductor laser (phased array laser) 11 that emits a laser beam 10 as pumping light, and the laser beam 10 that is divergent light.
Condenser lens 12 composed of, for example, a rod lens
And a YVO ₄ rod (hereinafter referred to as Nd: YVO ₄ ) which is a solid-state laser rod doped with neodymium (Nd).
A rod 13), and a resonator mirror 14 disposed in front of the Nd: YVO ₄ rod 13 (to the right in the figure). A KTP crystal 15 as a crystal of the first nonlinear optical material and a BBO crystal 16 as a crystal of the second nonlinear optical material are provided between the Nd: YVO ₄ rod 13 and the resonator mirror 14. Nd: YVO ₄ is disposed from the rod 13 side in this order. A phase compensator 17 acting as described later is disposed between the two crystals 15 and 16. The KTP crystal 15 can be controlled to a desired temperature by a Peltier element 18, a temperature sensor 19 for detecting the crystal temperature, and a temperature control circuit 20 receiving the output of the temperature sensor 19.

The components described above are mounted and integrated on a common housing (not shown). The temperature of the phased array laser 11 is controlled to a predetermined temperature by a Peltier device and a temperature control circuit (not shown).

As the phased array laser 11, a laser that emits a laser beam 10 having a wavelength λ ₁ = 809 nm is used. On the other hand, the Nd: YVO ₄ rod 13 emits a linearly polarized laser beam 21 having a wavelength λ ₂ = 1064 nm by exciting the neodymium atoms by the laser beam 10. This laser beam 21 is a KTP crystal
Incident on 15, is converted into the second harmonic wave 22 having a wavelength _{λ 3 = λ 2/2 =} 532 nm. Then, the second harmonic 22 and the laser beam 21 enter the BBO crystal 16 and have a wavelength λ ₄ =
The wavelength is converted to a sum frequency 23 of 355 nm. 1 / λ ₂ +
1 / λ ₃ = 1 / λ ₄ .

Here, coatings 30 and 31 are provided on the rear (outer) end face 13a and the front (inner) end face 13b of the Nd: YVO ₄ rod 13, respectively, and the rear end face 15 of the KTP crystal 15 is provided.
a, a coating 32 is provided on the rear end face 17 a of the phase compensator 17.
And coatings 33 and 34 on the front end face 17b, respectively.
However, coatings 35 and 36 are provided on the rear end face 16a and the front end face 16b of the BBO crystal 16, respectively, and a resonator mirror is provided.
The coating 37 is applied to the concave mirror surface 14a of the fourteenth embodiment. The wavelength λ ₁ of these coatings 30-37
= 809 nm, λ ₂ = 1064 nm, λ ₃ = 532 nm and λ
_The characteristics for ₄ = 355 nm are as follows. AR indicates non-reflection (transmittance of 99% or more), and HR indicates high reflection (reflectance of 99.9% or more).

Λ ₁ λ ₂ λ ₃ λ ₄ Coating 30 AR HR AR-〃 31-AR HR-〃 32-AR AR-〃 33-AR AR-〃 34-AR AR-〃 35-AR AR HR 〃 36- AR AR AR 〃 37-HR HR AR The laser beam 21 resonates between the end surface 13 a of the Nd: YVO ₄ rod 13 and the mirror surface 14 a because of the coatings 30 and 37 described above. Since the laser beam 21 is incident on the KTP crystal 15 in a state of resonance, the laser beam 21 is incident on the KTP crystal 15 with a high output, thereby generating the second harmonic 22 efficiently. This second harmonic 22 is also
Nd: YVO ₄ coated 31 and 37 respectively
It resonates between the end face 13b of the rod 13 and the mirror surface 14a, and enters the BBO crystal 16 together with the laser beam 21 which is also resonating as described above. As a result, the laser beam 21 and the second harmonic 22 also have a high output and a BBO crystal 16
May be incident. Then, the sum frequency 23 is reflected directly or on the end face 16 a of the BBO crystal 16 coated with the coating 35, and transmits through the resonator mirror 14.

As described above, in the present apparatus, the second harmonic
Although the resonator 22 is resonated, the resonator mirror for the second harmonic 22 is not inserted in the resonator of the laser beam 21, so that a loss occurs when the laser beam 21 passes through such a mirror. Absent. Therefore, a laser beam 21 having a higher intensity is incident on the KTP crystal 15 and the BBO crystal 16, so that high wavelength conversion efficiency can be obtained.

The Nd: YVO ₄ rod 13 has an end face 13
It is sufficiently possible to perform polishing so that the error in the parallelism between a and 13b is about 30 seconds or less. Like that Nd: YV
If the O ₄ rod 13 is polished, when the laser beam 21 is adjusted so as to be perpendicularly incident on the end face 13a in order to resonate the laser beam 21 well, the laser beam 21 naturally has a high accuracy on the rod end face 13b. At normal incidence. Therefore, even if the non-reflection property of the coating 31 with respect to the laser beam 21 deteriorates, the reflection loss of the laser beam 21 at the rod end face 13b becomes negligibly low,
This point also contributes to the improvement of the wavelength conversion efficiency.

As described above, since the resonator mirror for the second harmonic 22 is not inserted in the resonator of the laser beam 21, the number of parts can be reduced, and adjustment of the resonator mirror can be prevented. This does not occur, and the reliability of the device is also improved.

In the KTP crystal 15, a type II phase matching is established between the laser beam 21 and the second harmonic 22. Then, the polarization direction of the second harmonic 22 rotates about 45 ° with respect to that of the laser beam 21. In the BBO crystal 16, a type I phase matching is achieved between the laser beam 21 and the second harmonic 22 as the fundamental wave and the sum frequency 23. The phase compensator 17 adjusts the phases of the laser beam 21 and the second harmonic 22, and changes their polarization directions, which have been shifted by about 45 ° as described above before being incident thereon,
Align in almost the same direction. In this manner, the laser beam 21 and the second harmonic 22
When the light is incident on the BO crystal 16, the type I phase matching can be satisfactorily achieved, so that they can be efficiently summed.
Is converted to In this embodiment, when the output of the phased array laser 11 is 500 mW, a sum frequency 23 of 1 mW is taken.

The deviation of the polarization direction of the second harmonic 22 from the laser beam 21 is about 45 ° as described above, and the value changes according to the temperature of the KTP crystal 15. Therefore,
By adjusting the temperature of the KTP crystal 15 by the above-mentioned temperature control means so that the deviation of the polarization direction exactly matches the compensation by the phase compensating plate 17, the laser beam 21 and the second The harmonics 22 are in a state where the polarization directions are exactly aligned, and the type I phase matching can be achieved very well.

Next, a second embodiment of the present invention will be described with reference to FIG. In FIG. 2, the same elements as those in FIG. 1 are denoted by the same reference numerals, and redundant description thereof will be omitted.

In the apparatus of the second embodiment, a BBO crystal 40 is used instead of the KTP crystal 15 used in the apparatus of the first embodiment, and a phase compensator 41 is used instead of the phase compensator 17. I have. Front end face 40a of BBO crystal 40, phase compensator
Coatings 32, 33, and 34 similar to those in the first embodiment are applied to both end surfaces 41a and 41b of 41, respectively.

[0024] In this device, the resonator mirror 14 is also used for the laser beam 21 and the second harmonic wave 22, and Nd: YVO ₄ resonator mirror surface outer end surface 13a of the laser beam 21 of the rod 13, at the same Since the inner end surface 13b formed in parallel is a resonator mirror surface for the second harmonic 22, the same operation and effect as in the first embodiment can be obtained.

In the BBO crystal 40 as a crystal of the first nonlinear optical material, a type II phase matching is established between the laser beam 21 and the second harmonic 22, and the polarization of the second harmonic 22 Direction is about 45 for that of laser beam 21
° rotate. Then, the phase compensating plate 41 adjusts the phases of the laser beam 21 and the second harmonic 22 so as to eliminate the shift of the polarization direction of 45 °. So in this case too,
In the BBO crystal 16, the type I phase matching between the laser beam 21 and the second harmonic wave 22 and the sum frequency 23 is favorably achieved, and the sum frequency 23 can be obtained efficiently.

Also in this case, by adjusting the temperature of the BBO crystal 40, the polarization directions of the laser beam 21 and the second harmonic 22 incident on the BBO crystal 16 can be accurately matched.

As described above, the BBO crystal 40 or the first
Means for adjusting the temperature of the KTP crystal 15 of the embodiment is not necessarily required, but providing such a means is more advantageous in realizing high conversion efficiency as described above.

In place of the BBO crystal, an LBO crystal or the like may be used. Further, as a laser medium, Nd:
Instead of _{YVO 4 Nd: YLF, Nd:} YAG, NA
B, Nd: LiNbO ₃ , NYAB, LNP, or the like can be used.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a first embodiment of the present invention.

FIG. 2 is a schematic side view showing a second embodiment of the present invention.

[Explanation of symbols]

10 Laser beam (pumping light) 11 Semiconductor laser 13 Nd: YVO ₄ rod 13 a Nd: YVO ₄ rod outer end face 13 b Nd: YVO ₄ rod inner end face 14 Resonator mirror 15 KTP crystal 16, 40 BBO crystal 17, 41 Phase Compensator 18 Peltier element 19 Temperature sensor 20 Temperature control circuit 21 Laser beam (solid laser oscillation beam) 22 Second harmonic 23 Sum frequency 31, 32, 33, 34, 35, 36, 37 Coating

Claims (2)

(57) [Claims] A laser beam obtained by pumping a solid-state laser medium is incident on a crystal of a first nonlinear optical material disposed in a solid-state laser resonator to generate a second harmonic. In a light wavelength conversion device for generating a sum frequency by making a harmonic and the laser beam incident on a crystal of a second nonlinear optical material, one mirror constituting a solid-state laser resonator has a second harmonic resonator. The outer end face of the solid-state laser medium is coated with the other mirror of the solid-state laser resonator, and the inner end face of the solid-state laser medium is resonated with the second harmonic. An optical wavelength conversion device, wherein the optical wavelength conversion device is provided with a coating to be the other mirror of the vessel. 2. The optical wavelength converter according to claim 1, wherein an outer end face and an inner end face of the solid-state laser medium are formed parallel to each other.