JPH04192574A - Frequency-sweep laser apparatus - Google Patents

Abstract

PURPOSE:To enhance the efficiency of a laser amplification operation and to ensure the output of a laser beam by a method wherein a polarization element is inserted between a frequency sweeping means and a laser amplification means and the polarization characteristic of the laser beam which is incident on the laser amplification means is set to be optimum. CONSTITUTION:A laser beam L2 which has been frequency-sweep is passed through a polarization element 70 which has been inserted between a crystal 31 inside a frequency sweeping means 30 and a laser amplification medium 51 inside a laser amplification means 50. Thereby, its polarization direction is corrected and its polarization characteristic is set to be optimum. The laser beam L2 whose polarization characteristic has been adjusted in this manner is passed through the laser amplification medium 51 inside the laser amplification means 50; it is amplified; it is radiated as a final laser medium L3. At this time, the polarization characteristic of the laser beam L2 which is incident on the laser amplification means 50 is corrected so as to be optimum with reference to the laser amplification medium 51. Thereby, the amplification efficiency of the laser amplification means 50 is enhanced, and the large-output laser beam L3 can be obtained by the small number of amplification stages.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a frequency sweep laser device in which the oscillation spectrum of laser light covers the light absorption spectrum width of irradiation target particles (hereinafter simply referred to as irradiation target). In particular, the present invention relates to a frequency swept laser device with improved amplification efficiency of laser light after frequency sweeping.

[Prior Art] Generally, laser light using a dye laser medium is used in the field of spectroscopy because its wavelength can be changed continuously in the ultraviolet and near-infrared regions before and after the visible region. For example, it is used for selective excitation or isotope separation of an irradiation target by utilizing the light absorption effect of the irradiation target.

At this time, the light absorption characteristics of the irradiation target have a certain range with respect to the frequency of light, so in order to perform highly efficient selective excitation, it is necessary to have an oscillation spectrum that sufficiently covers the light absorption spectrum of the irradiation target. A laser beam consisting of

Conventionally, frequency-swept dye laser light covers the light absorption spectrum of the irradiation target as shown in Figure 2.
It is used for uranium enrichment because it can create adiabatic inversion in the energy state of the irradiation target and can perform particularly highly efficient selective excitation and isotope separation.

FIG. 3 is a block diagram illustrating a conventional frequency swept laser device, as described, for example, in U.S. Pat. No. 4,636,287 by Pike et al.

In the figure, (10) is the laser beam L1 with a narrow spectrum width.
It is a laser oscillator that emits, for example, a CW (continuous wave) type dye laser medium (11) and a wavelength selection element (12) arranged coaxially with the dye laser medium (11).
, a dye laser medium (11) and a wavelength selection element (12)
A total reflection mirror (1
3) and a partially reflecting mirror (14).

The wavelength selection element (12) is composed of, for example, a birefringence filter, an etalon, a diffraction grating, etc., and is provided as necessary.

(20) is an excitation laser for exciting the laser oscillator (10), and is adapted to emit excitation laser light LO, such as an excimer laser or an argon laser, to the dye laser medium (11). Furthermore, the excitation laser (20) is
Any device that can excite the single dye laser medium (11), such as a copper vapor laser, a nitrogen laser, a harmonic of a YAG laser, or a flash lamp, may be used.

(30) is a frequency sweeping means for sweeping the frequency of the laser beam L1 emitted from the laser oscillator (10), and is a crystal (31) arranged so that the laser beam L1 passes through.
) and a power amplifier (32) for applying a voltage signal E to the crystal (31).

The crystal (31) is made of an electro-optical element, for example, Li
Nb0. , LiTaO5, KDP, ^DP, DKDP
, DADP, etc. In addition, a power amplifier (32
) is made of semiconductor elements and is capable of direct switching.

(40) is an oscillator that generates a frequency signal for driving the power amplifier (32).

(50) is the laser beam L passing through the frequency sweeping means (30).
It is a laser amplification means for amplifying the laser beam L.
The laser amplification medium (51) made of a dye solution or the like is arranged so that the laser amplification medium (51) passes through the laser amplification medium (51), and an amplification excitation source (52) for exciting the laser amplification medium (51).

The amplification excitation source (52) is composed of, for example, a copper vapor laser, an excimer laser, an argon laser, a krypton laser, a nitrogen laser, a harmonic of a YAG laser, a flash lamp, etc., and the laser amplification medium (51) Anything that can excite can be used.

L3 is a laser beam that is frequency swept, amplified, and finally output.

(60) is a detector connected to the oscillator (40),
Together with the oscillator (40), it constitutes a timing control means, and synchronizes the amplification timing of the laser beam L2 with the frequency sweep timing.

Next, the operation of the conventional frequency sweep laser device shown in FIG. 3 will be described with reference to the explanatory diagram of FIG. 2 showing the frequency sweep state.

The dye laser medium (11) in the laser oscillator (10) is
It is excited by the excitation laser beam LO from the excitation laser (20), and oscillates in a single longitudinal mode spectrum by the wavelength selection element (12), the total reflection mirror (13), and the partial reflection mirror (14).

The laser beam L1 emitted from the laser oscillator (10) is
It passes through the crystal (31) in the frequency sweep means (30).

At this time, the crystal (31) is equipped with a power amplifier (32) driven by the frequency (for example, several kHz) of the oscillator (40).
A voltage signal E having a predetermined amplitude and a predetermined frequency is applied. Therefore, the refractive index of the crystal (31) changes, and as a result, the laser beam L1 undergoes phase modulation, the frequency is swept as shown by the arrow in Figure 4, and the light absorption spectrum of the irradiation target (see Figure 2). ) becomes a laser beam L2 that covers the area. The frequency sweep amount of the laser beam L2 at this time is crystal (3
1) and the rising speed of the voltage signal E, that is, the capacity of the power amplifier (32).

The laser light L2 frequency-swept in this way then passes through the laser amplification medium (51) in the laser amplification means (50). At this time, the laser amplification medium (51) is excited by the amplification excitation source (52), and the amplification excitation source (52)
2), the light emission timing is controlled by the output of the detector (60) which detects the frequency signal of the oscillator (40). Therefore, in synchronization with the frequency sweep, a portion of the laser beam L2 that is close to a linear sweep is amplified by the laser amplification medium (51), and is output as the final laser beam L3.

By the way, the crystal (30) in the frequency sweep means (30) and the laser amplification medium (51) in the laser amplification means (50)
has polarization characteristics for the incident laser beams Ll and L2, respectively. Therefore, if the laser beams Ll and L2 are not set to optimal polarization characteristics, the crystal (31) and the laser amplification medium (51) cannot sufficiently achieve the frequency sweep function and the amplification function.

Therefore, a polarizing element (not shown) is usually placed on the laser beam incident side of the crystal (31), and is set so that the laser beam L1 has optimal polarization characteristics for the crystal (31). There is. However, since no measures have been taken on the incident side of the laser amplification medium (51), if the optimum polarization characteristics are not set due to installation errors of the laser amplification medium (51), the laser beam L2 may not be There is a possibility that it cannot be amplified. In particular, since the polarization direction of the laser beam L2 that has passed through the crystal (31) has been rotated, the laser beam L2
It is difficult to optimally install the laser amplification medium (51) for the laser amplification medium (51).

[Problems to be Solved by the Invention] As described above, the conventional frequency sweep laser device converts the laser beam L2 from the frequency sweep means (30) into the laser amplification means (
50), there was a problem in that the amplification efficiency decreased.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve the laser amplification efficiency and obtain a frequency swept laser device that can secure a sufficient output of laser light.

[Means for Solving the Problems] A frequency sweep laser device according to the present invention has a polarizing element inserted between a frequency sweep means and a laser amplification means.

[Operation] In the present invention, the polarization direction of the laser beam is rotated by the polarizing element to optimally set the polarization characteristics of the laser beam incident on the laser amplification means.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure is a configuration diagram showing one embodiment of the present invention, (10)
~(60) are similar to those described above.

The detector (60) that controls the amplification timing may be configured with a delay circuit.

(70) is a polarizing element inserted between the crystal (31) in the frequency sweep means (30) and the laser amplification medium (51) in the laser amplification means (50), such as a quartz plate or a mica plate ( It is composed of a combination of λ/4 plates that perform 1/4 rotational correction for the wavelength λ of the laser beam L2.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained.

The laser oscillator (10) excited by the excitation laser beam LO from the laser excitation source (20) emits, for example, a single longitudinal mode laser beam L1 with a narrow spectral width as described above, ) sweeps the frequency of the laser beam L1 through the crystal (31) as indicated by the arrow in FIG.

The frequency-swept laser beam L2 passes through a polarizing element (70), so that the polarization direction is corrected and the polarization characteristics are set to be optimal for the laser amplification medium (51). The laser light L2 whose polarization characteristics have been adjusted in this way passes through the laser amplification medium (51) in the laser amplification means (50), is amplified, and is emitted as the final laser light L3.

At this time, since the polarization characteristics of the laser beam L2 incident on the laser amplification means (5o) are corrected to be optimal for the laser amplification medium (51), the amplification efficiency of the laser amplification means (50) is is improved, and a high-output laser beam L3 can be obtained with a small number of amplification stages.

Therefore, by using a small laser amplification means (50), highly efficient selective excitation or isotope separation is performed on the irradiation target, and the optical absorption spectrum of the irradiation target is covered, so that the energy state of the irradiation target is in an adiabatic inversion state. can be produced.

[Effects of the Invention] As described above, according to the present invention, a polarizing element is inserted between the frequency sweeping means and the laser amplifying means to rotationally correct the polarization direction of the frequency swept laser beam, and the laser amplifying means Since the polarization characteristics of the laser beam incident on the laser beam are optimally set, the laser amplification efficiency is improved and a frequency swept laser device that is small and can emit a high-output laser beam can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, Fig. 2 is an explanatory diagram showing the light absorption spectrum of a general irradiation target, and Fig. 3 is an explanatory diagram showing the light absorption spectrum of a general irradiation target.
This figure is a configuration diagram showing a conventional frequency sweep laser device, and FIG. 4 is an explanatory diagram showing a general frequency sweep state. (10)...Laser oscillator (30)...Frequency sweep means (31)...Crystal (50)...
・Laser amplification means (51)...Laser amplification medium (7
0)...Polarizing elements L1 to L3...Laser light E
. . . Voltage signal plane. In the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] A laser oscillator that emits laser light with a narrow spectral width, and a crystal arranged so that the laser light passes through,
It includes a frequency sweeping means for sweeping the frequency of the laser beam by phase modulation when a voltage signal is applied to the crystal, and a laser amplification medium arranged so that the laser beam passed through the frequency sweeping means. , a frequency swept laser device comprising a laser amplifying means for amplifying the frequency swept laser light, a polarizing element being inserted between the frequency sweeping means and the laser amplifying means, and a polarizing element being inserted into the laser amplifying means. A frequency sweep laser device characterized by optimally setting the polarization characteristics of an incident laser beam.