JPH0513890A - Dye laser oscillator - Google Patents

Abstract

PURPOSE:To obtain a dye laser oscillator having a high efficiency and a narrow band by using a prism as a coupler so as to produce a laser output, operating a transmitted light of the prism at a diffraction grating or an etalon as a wavelength selecting element, and producing a reflected light as a laser output. CONSTITUTION:An optical amplifier is formed of a dye cell 1, a reflecting element for constituting a resonator is formed of a diffraction grating 3, other reflecting element is formed of a totally reflecting mirror 4, a prism 5 for producing a laser light, and an etalon 9 having an operation for narrowing a wavelength width. Since a reflected light on the surface of a prism is used, which was heretofore a larger loss as a beam width is increased more in prior art, its efficiency is enhanced more as compared with that of the prior art, and since an absolute amount of an operating light 7 which contributes to narrowing in the band, is increased, it can be narrowed more as compared with that of the prior art. Thus, higher efficiency than that of the prior art can be obtained, and narrower wavelength width can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a narrow band dye laser device, and more particularly to a dye laser oscillator suitable for use in uranium isotope separation.

[0002]

2. Description of the Related Art Generally, a device for irradiating a dye solution in a dye cell with light to cause laser oscillation is known as a dye laser oscillator. Many applications are being made by utilizing the characteristics that the oscillation wavelength range is wide and the band can be narrowed. Among them, isotope separation of uranium and the like (French Patent No.
2,311,432 and JP-A-1-220878).
This utilizes the difference in the spectroscopic spectrum between isotopes to selectively ionize one isotope and apply an electric field or magnetic field to it to separate it from other isotopes in the neutral state. Is the way to do it. For example, uranium 235 and uranium 238 utilize their spectral difference of about 8Å.
In this case, the wavelength width of the separation dye laser needs to be narrowed to a few Å or less. As a typical structure for narrowing the wavelength width of the dye laser, the Hensch type shown in FIG. 2 is known. This is to narrow the wavelength band by inserting a wavelength selection element such as a prism 5 or an etalon 9 into a kind of Fabry-Perot resonator configured by providing a semitransparent mirror 10 and a diffraction grating 3 at both ends of a dye cell 1. Is intended. The laser output is taken out through the semi-transparent mirror 10.

[0003]

In order to narrow the band of the laser output, it is necessary to widen the beam width to act on the diffraction grating or the etalon which is the wavelength selection element. However, in such a conventional configuration, since the reflection on the prism surface, which is lost as the beam width is expanded, increases, it is inevitable that the efficiency is lowered.

An object of the present invention is to eliminate the above drawbacks and to provide a highly efficient narrow band dye laser oscillation device.

Conventionally, the ratio (coupling ratio) of the amount of light extracted from the resonator to the outside and the amount of light returned to the inside has been adjusted by a semi-transmissive mirror. However, this has different transmittances prepared in advance. It is necessary to select an appropriate one from a plurality of semi-transmissive mirrors and replace them each time adjustment is performed, which is troublesome to prepare a large number of semi-transmissive mirrors for precise adjustment.

A second object of the present invention is to provide a dye laser oscillating device which eliminates the above drawbacks and which can continuously change the value of the coupling ratio with one optical element and which can be easily adjusted. is there.

A third object of the present invention is to provide a highly efficient dye laser oscillation device when a prism is used for the coupler.

A fourth object of the present invention is to provide a narrow band dye laser oscillation device when a prism is used for the coupler.

A fifth object of the present invention is to provide a dye laser oscillating device in which, when a prism is used as a coupler, it is easy to monitor the oscillation wavelength and wavelength width during operation.

A sixth object of the present invention is to use an ASE (Amplif) included in the laser output when a prism is used for the coupler.
An object of the present invention is to provide a dye laser oscillating device having a small amount of ied spontaneous emission.

A seventh object of the present invention is, when a rotatable prism is used for the coupler, a dye laser oscillation which can correct an optical axis changed by rotating the prism and can always maintain a constant optical axis. To provide a device.

[0012]

A prism is used as a coupler for extracting a laser output, and light transmitted through the prism is caused to act on a diffraction grating, an etalon, or the like, which is a wavelength selection element, and reflected light is extracted as a laser output.

By this means, the prism can be rotated.

When the prism is used as a coupler, the other reflecting element constituting the resonator is a total reflection mirror, a diffraction grating, a semi-transmission mirror or a narrow band reflection mirror.

When a rotatable prism is used as the coupler, a pair of folding reflecting mirrors are provided to further reflect the reflected light (extracted light) on the prism surface.

[0016]

In the present invention, the prism is used as a coupler instead of the conventional semi-transmissive mirror by utilizing the property that a part of the light incident on the prism surface is reflected and the rest is transmitted. Since the reflected light on the prism surface, which was conventionally discarded, is used here, high efficiency can be achieved.

If the prism is rotatable, the ratio of the transmitted light and the reflected light (coupling ratio) can be continuously changed by changing the incident angle of the light on the prism surface.
Easy to adjust.

Further, in the present invention in which the prism is used as the coupler, the other reflection element constituting the resonator is a total reflection mirror, so that the optical loss in the resonator is minimized, so that high efficiency can be obtained. .

Further, in the present invention, the other reflecting element constituting the resonator is a diffraction grating, so that the resonator can be constituted by a pair of diffraction gratings. In this case, the light in the resonator is doubled. Since it interacts with the diffraction grating at a frequency of, a narrow wavelength width can be obtained.

Further, in the present invention, the other reflecting element constituting the resonator is a semi-transmissive mirror, whereby a part of the light in the resonator can be extracted to the outside under the condition that the optical axis is constant. Therefore, it is possible to monitor the wavelength and the wavelength width with a fixed-position monitor device at any time even during operation.

Further, in the present invention, if the other reflecting element constituting the resonator is a narrow band reflecting mirror, the narrow band reflecting mirror acts as a total reflecting mirror only in a wavelength region near the oscillation wavelength, and therefore, from the oscillation wavelength. The ASE component with the deviated wavelength escapes from this end to the outside. Therefore, the amount of ASE contained in the laser output taken out from the prism at the other end is reduced.

Further, in the present invention in which the rotatable prism is used as the coupler, it is necessary to correct the optical axis which changes due to the rotation of the prism which is the coupler. Therefore, a pair of folding reflecting mirrors are provided, one is fixed to a support that can be rotated and translated, and the other is fixed to a support that is rotatable. Translated so that the extracted light is irradiated on the rotation axis of the former reflection mirror,
The rotation of the former folding reflecting mirror is adjusted so that the reflected light is irradiated onto the rotation axis of the latter folding reflecting mirror. The latter reflecting mirror has a fixed position, and the extracted light is always radiated on the rotation axis, so that a constant optical axis can be maintained by adjusting the rotation.

[0023]

The present invention will be described with reference to FIG. As a light amplification part, a dye cell 1, a reflection element for forming a resonator, a diffraction grating 3, another reflection element for a total reflection mirror 4, a prism 5 for extracting a laser output, and a function for narrowing the wavelength width. Composed of etalon 9. Excitation light 2 is applied to the dye cell 1 to generate reciprocating light 6. The reciprocating light 6 is split by the prism 5 into operation light 7 and extraction light 8, and the extraction light 8 is used as a laser output.

The specifications of the constituent materials used here are as follows.

Dye cell 1 Fused silica glass diffraction grating 3 Lattice line density 600 lines / mm Total reflection mirror 4 Reflectivity 99.9% Prism 5 Fused silica glass etalon 9 Free spectrum range 10GH
z, finesse 20 Next, the operation will be described. Rhodamine 6
A solution in which the G dye was dissolved in ethanol having a purity of 90% or more at a ratio of 0.4 millimoles per liter was passed through the dye cell 1, and the excitation light 2 (wavelength 510 nm, output 1
A 1.8 watt copper vapor laser) was irradiated from the side. In this case, the Rhodamine 6G dye was excited, and the round-trip light 6 was generated in the resonator formed by the diffraction grating 3 and the total reflection mirror 4. However, the reciprocating light 6 is P-polarized and is divided into the operation light 7 and the extracted light 8 by the prism 5. The ratio can be expressed as follows according to the law of optics, where θ is the angle with respect to the normal to the prism surface.

[0026]

[Equation 1] [Ratio of extracted light 8] = [(cos θ · sin θ−cos α · sin α) / (cos θ · sin θ + cos α · sin α)] ² [Ratio of operation light 7] = 1- [strength of extracted light 8] {where α = arcsin [(sin θ) / n], n is the refractive index of the fused silica glass of the prism 5} The prism 5 for the round trip light 6 Was fixed by an optical element support having an angle adjusting mechanism, and the angle was changed to examine the relationship between the increase and decrease in the ratio of the extracted light 8 and the wavelength width. As a result, they have found that there is an optimum ratio that minimizes the wavelength width. That is, if the ratio of the extracted light 8 is increased, the efficiency is increased, but the amount of light acting on the diffraction grating 3 or the etalon 9 which is the wavelength selection element is decreased, so that the wavelength width is increased. On the contrary, if the ratio of the extracted light 8 is reduced, the amount of the extracted light decreases (on the other hand, the size of ASE is always almost constant), the influence of ASE becomes strong, and the wavelength width also becomes large. In the experiment, the minimum wavelength width of 0.75 GHz was obtained when the angle θ was about 85 degrees. In this case, the ratio of the extracted light 8 can be calculated to be about 50% (having the same physical meaning as the transmissivity of the semitransparent mirror) from the above-mentioned law. The laser output (extracted light 8) at this time was 450 milliwatts (efficiency: 0.45 /
11.8 = 3.8%), and the absolute wavelength was 593 nanometers.

Further, for comparison with the conventional system, the total reflection mirror 4 was replaced with a semi-transmission mirror having a transmittance of 96%, and oscillation was made with the configuration of FIG. As a result, the wavelength width is 5.5 GHz, the laser output (extracted light 8) is 96 mW (efficiency: 0.096 / 1).
The value was 1.8 = 0.8%). The transmissivity of 96% of the semi-transmissive mirror was experimentally selected so that the laser output (extracted light 8) was maximized.

In the present invention, since the reflected light on the prism surface, which has been a large loss as the beam width is widened in the past, is used, the efficiency can be improved by 4.7 times compared with the conventional one, and the band narrowing can be achieved. Since the absolute amount of the operation light 7 that contributes to the increase becomes large, the band can be narrowed to about 1/7 of the conventional wavelength width.

By the way, even if the transmissivity of the semi-transmissive mirror is set to 50% in the conventional structure, the minimum wavelength width obtained in the present invention cannot be obtained. The reason is that the intensity of the reciprocating light 6 is different from that of the present invention because the reflection at the prism 5 is lost as the lost light 11. The optimum value of this transmittance generally changes depending on the intensity of the excitation light 2. In the conventional configuration,
Each time, it was necessary to reselect and replace a semi-transmissive mirror having an optimum transmittance, but in the present invention, if the angle of the optical element supporting member to which the prism 5 is fixed is readjusted, it is clear from the above law. Thus, the ratio (coupling ratio) between the operation light 7 and the extracted light 8 can be continuously changed. This operation only requires the operation of the angle adjusting screw, and is easier than the work of replacing the semi-transparent mirror, which was necessary in the past.

A second embodiment of the present invention is shown in FIG. The other reflecting element forming the resonator is the diffraction grating 12, and the resonator is formed by a pair of diffraction gratings. Once the optical axes are aligned, the light inside the resonator is diffracted at both ends by the diffraction gratings 3, 12
Therefore, a narrower wavelength width can be obtained. The total reflection mirror 4 in FIG.
As a result of oscillating under the above-mentioned experimental conditions by substituting it with 2, a wavelength width of 0.55 GHz and a laser output (extracted light 8) of 6 milliwatts were obtained.

A third embodiment of the present invention is shown in FIG. The other reflective element constituting the resonator is a semi-transmissive mirror 13. Therefore, a part of the light inside the resonator can be extracted as the monitoring light 14 under the condition that the optical axis is constant. The total reflection mirror 4 in FIG. 1 was replaced with a semi-transmission mirror 13 having a transmittance of 0.2%, and the wavelength and wavelength width were constantly monitored by the position-fixed monitor device 15 during operation. In this case, the effect of replacing the total reflection mirror 4 with the semi-transmission mirror 13 was not observed in the observation values of the laser output and the wavelength width.

A fourth embodiment of the present invention is shown in FIG. The other reflection element constituting the resonator is a narrow band reflection mirror 16. The reflectance is about 80% over the wavelength range of 1000 GHz near the oscillation wavelength, and the narrowband reflector 16 having a reflectance of 5-10% in other wavelength ranges is replaced with the total reflection mirror 4 in FIG. As a result of oscillating, 29
It was observed that milliwatts of ASE light 17 exited the narrow band reflector 16. Therefore, laser output (extracted light 8)
Of the AS included in the wavelength width of the
E minutes were reduced by approximately 30%.

The fifth embodiment of the present invention is shown in FIG. Since the rotatable prism 5 is used as a coupler, when the prism 5 is rotated, it is necessary to correct the optical axis that changes each time. Therefore, the pair of folding reflecting mirrors 18, 1
9, the folding reflecting mirror 18 is fixed to a support that can be rotated and translated, and the folding reflecting mirror 19 is fixed to a rotatable support. The correction procedure is as follows. First, the extracted light 8 is reflected by the reflecting mirror 1.
It is moved in parallel so that it is irradiated onto the rotation axis of 8, and secondly, the rotation of the reflection mirror 18 is adjusted so that the reflected light 20 is irradiated onto the rotation axis of the reflection mirror 19. Thirdly, the rotation of the folding reflecting mirror 19 is adjusted. Folding mirror rotation 19
Can be fixed in position, and the reflected light 20 can be always radiated onto this rotation axis, so that the optical axis of the laser output (irradiation light 21) can be kept constant by adjusting the rotation angle.
Note that this adjustment can be performed manually or by a computer in which the prism 5 and the folding reflecting mirrors 18 and 19 are linked.

Up to this point, the case where the number of the prism 5 is one has been described, but the same applies to a combination of a plurality of prisms. Although the etalon 9 is extremely effective for narrowing the wavelength band, it is not an essential component of the present invention and can be omitted depending on the situation.

[0035]

According to the present invention, since the reflected light on the prism surface, which has been a large loss as the beam width is widened in the past, is used in reverse, a higher efficiency can be obtained as compared with the conventional one.

Further, the value of the coupling ratio can be continuously changed by adjusting the angle of the optical element supporting member to which the prism 5 is fixed, which facilitates the adjustment.

Further, since the other reflection element constituting the resonator is a total reflection mirror, the optical loss in the resonator can be minimized, so that high efficiency can be obtained.

Further, since the other reflection element forming the resonator is a diffraction grating, the light in the resonator acts on the diffraction grating twice as often, so that a narrow wavelength width can be obtained.

Further, by using a semi-transmissive mirror as the other reflecting element constituting the resonator, a part of the light in the resonator can be taken out and the monitor device can monitor the wavelength and the wavelength width at any time during operation. Become.

If the other reflection element constituting the resonator is a narrow band reflector, the ASE component having a wavelength outside the oscillation wavelength will escape to the outside from this end, so the ASE component contained in the laser output. Decreases.

A fixed optical axis can be maintained by providing a pair of folding reflecting mirrors and adjusting their relative positions.

[Brief description of drawings]

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

FIG. 2 is a side view showing a conventional example.

FIG. 3 is a side view showing a second embodiment of the present invention.

FIG. 4 is a side view showing a third embodiment of the present invention.

FIG. 5 is a side view showing a fourth embodiment of the present invention.

FIG. 6 is a side view showing a fifth embodiment of the present invention.

[Explanation of symbols]

1 ... Dye cell, 2 ... Excitation light, 3 ... Diffraction grating, 4 ... Total reflection mirror, 5 ... Prism, 6 ... Reciprocating light, 7 ... Operation light, 8 ... Extracted light, 9 ... Etalon.

Claims (7)

[Claims] 1. A dye laser oscillating device comprising a dye cell, a reflecting element, a prism, a diffraction grating and an etalon, wherein reflected light of the prism is taken out of a resonator. 2. The dye laser oscillating device according to claim 1, wherein the prism is rotatable, and the ratio between the operation light and the extracted light is continuously changed by rotating the prism. 3. The dye laser oscillator according to claim 1, wherein the reflecting element is a total reflection mirror. 4. The dye laser oscillator according to claim 1, wherein the reflective element is a diffraction grating. 5. The dye laser oscillator according to claim 1, wherein the reflective element is a semitransparent mirror. 6. The dye laser oscillator according to claim 1, wherein the reflecting element is a narrow band reflecting mirror. 7. The dye laser oscillator according to claim 2, wherein a pair of folding reflecting mirrors for reflecting the extracted light are provided.