JPH04192577A - Laser frequency sweeping apparatus - Google Patents

Abstract

PURPOSE:To sufficiently ensure the frequency sweeping amount of a laser beam by using a voltage signal having a low voltage value by a method wherein a frequency sweeping means is provided with a plurality of power amplifiers used to apply a plurality of voltage signals to a crystal and the action timing operation of the plurality of power amplifiers is controlled individually by using a timing control means. CONSTITUTION:Voltage signals Ea to Ec from power amplifiers 32a to 32c which are actuated by a frequency from an oscillator 40 are applied to a crystal 31; a laser beam L1 which is passed through the crystal 31 is phase-modulated by a change in the refractive index of the crystal 31; a frequency is swept. The amplification timing operation of a laser beam L2 by an excitation source 52 for amplification use and by a laser amplification medium 51 is adjusted by a delay circuit 60d. When a plurality of voltage signals Ea to Ec are applied to the crystal 31 at a frequency sweeping means 3OA in this manner, a frequency sweeping amount can be ensured sufficiently by a comparatively low voltage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser frequency sweep device in which the oscillation spectrum of laser light covers the light absorption spectrum width of particles to be irradiated (hereinafter simply referred to as irradiation target). In particular, the present invention relates to a laser frequency sweep device that can ensure a frequency sweep amount (frequency change amount) using a voltage signal with a low voltage value. □ [Prior art] Laser light using a dye laser medium is generally used in the field of spectroscopy because its wavelength can be changed continuously in the ultraviolet and near-infrared regions around 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 can create an adiabatic inversion in the energy state of the irradiation target by covering the light absorption spectrum of the irradiation target, which enables particularly highly efficient selective excitation and isotope separation. , used for uranium enrichment, etc.

FIG. 8 is a block diagram illustrating a conventional laser frequency sweep 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).

(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) consists of an electro-optical element, for example L!
NbO3, LiTa0:+, KDP, ^DP, DKD
It is composed of P, DADP, etc. In addition, a power amplifier (3
2) is made of a semiconductor element and is capable of direct switching. The power amplifier (32) determines the amplitude EO, frequency ω, etc. of the voltage signal E.

(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

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 laser frequency sweep device shown in FIG. 8 will be described with reference to the voltage signal waveform diagram in FIG. 9 and the frequency variation waveform diagram in FIG. 10.

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).
Accordingly, a voltage signal E having a predetermined amplitude EO and a predetermined frequency ω is applied. Therefore, the refractive index of the crystal (31) changes, and as a result, the laser beam L1 undergoes phase modulation and frequency is swept, becoming a laser beam L2 that covers the light absorption spectrum of the irradiation target. The frequency sweep amount (frequency change amount ΔΩ) of the laser beam L2 at this time is proportional to the size of the crystal (31) 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.

For example, if the voltage signal E applied to the crystal (30) is
When the voltage signal E'(
t) is E (t) = −Eo ・cos(ωt)
-Represented by ■. However, Eo is the amplitude of the voltage signal E (t), and ω is the angular frequency of the voltage signal E (t). At this time, the frequency change amount ΔΩ of the frequency-swept laser beam L2 is given by ΔΩ(t)=dE(t)/dt=ωEo−sin(ωt)−■ as a function of time t, and FIG. become that way.

Therefore, by adjusting the excitation timing of the amplification excitation source (52) using the detector (60), only the frequency change region from time t1 to t2 can be amplified and extracted as the final laser beam L3.

[Problem to be solved by the invention] As described above, the conventional laser frequency sweep device uses a crystal (3
Since a single voltage signal E is applied to 1), in order to ensure a sufficient frequency sweep amount of the laser beam L3,
It is necessary to increase the amplitude Eo and angular frequency ω of the voltage signal E, or to increase the size of the crystal (31), resulting in a problem that the device becomes larger.

This invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a laser frequency sweep device that can secure a sufficient frequency sweep amount of laser light using a voltage signal with a low voltage value. .

[Means for Solving the Problems] A laser frequency sweep device according to the present invention is provided with a plurality of power amplifiers for applying a plurality of voltage signals to a crystal.

Further, a laser frequency sweep device according to another aspect of the present invention is provided with a plurality of control circuits for driving a crystal with a plurality of voltage signals.

[Operation] In this invention, a plurality of voltage signals with relatively low voltage values are applied to the crystal to control the frequency sweep amount and sweep speed of the laser beam, and cover the light absorption spectrum of the irradiation target within a predetermined time. ensure sufficient frequency sweep amount.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1st
The figure shows the constituent countries of an embodiment of this invention (30A
) corresponds to the frequency sweep means (30), and (10)
, (31), (40) and (50) to <bz> are the same as described above.

(20A) is a laser excitation source corresponding to the excitation laser (20), for example, copper vapor laser, argon laser, krypton laser, excimer laser, nitrogen laser, YAG
It consists of harmonics of lasers, flash lamps, etc. Here, a case is shown in which the laser excitation source (20A) emits excitation laser light LO.

(32a) to (32c) are a plurality of power amplifiers provided in the frequency sweep means (30A), and are adapted to apply individual voltage signals Ea to Ec to the crystal (31).

Delay circuits (60a) to (63d) serve as timing control means, and are synchronously driven and controlled by an oscillator (40). Among these, delay circuits (60a) to (60c
) also controls the application timing of the voltage signals Ea to Ec, and the delay circuit (60d) is used for excitation for amplification. The operation timing of the source (52), that is, the amplification timing of the laser beam L2 is controlled.

Note that although a case in which there are three power amplifiers is shown here, any number of power amplifiers may be provided, and a number of delay circuits corresponding to the number of power amplifiers may be similarly provided.

Next, the operation of the embodiment of the present invention shown in FIG. 1 will be explained with reference to the waveform diagrams of FIGS. 2 to 5.

The laser oscillator (10) excited by the excitation laser beam 1.0 from the laser excitation source (20A) emits, for example, a single longitudinal mode laser beam L1 with a narrow spectral width as described above.

On the other hand, the crystal (31) is applied with voltage signals Ea to Ec from power amplifiers (32a) to (32c) that operate according to the frequency of the oscillator (40), and the laser beam L1 passing through the crystal (31) is applied to the crystal (31). undergoes phase modulation due to the change in the refractive index of the crystal <31), and the frequency is swept. At this time, the frequency sweep amount (frequency change amount Δω) and frequency sweep speed (frequency sweep time) of the laser beam L2 are controlled by the voltage signals Ea to Ee from the respective power amplifiers (32a) to (32c).

For example, from each power amplifier (32a) to (32c)
When a voltage signal E similar to that shown in the figure is generated and applied to the crystal (31) as Ea=Eb=Ec=E, the frequency sweep amount of the laser beam L2 becomes three times that of the conventional one. Therefore, the amplitude Eo of each voltage signal E may be 1"/3 of the conventional value, and the required sweep amount can be secured with the low voltage signals Ea to Ec.

Furthermore, when two power amplifiers (32a) and (32b) are used to generate voltage signals Ea (broken line) and Eb (-dotted chain line), respectively, as shown in FIG. 2, each voltage with respect to time t The signals Ea(t) and Eb(t) are E a
(t)= −E o°C05(ωt)E b(t)=
E o −cos(2ωt)/2. in this case,
The voltage signal E actually applied to the crystal (31) is a voltage signal Eab (solid line) that is a combination of the voltage signals Ea and Eb, and as a function of time t, E ab(t) = -Eo・
cos(ωt)+Eo・cos(2ωt)/2...
■ Represented by.

Therefore, the frequency change amount ΔΩab(t) of the laser beam L2 after frequency sweeping in this case is ΔΩab(t)=ΔΩa(t)+ΔΩb(t)=ωEO
°5in(ωt) -ωE olsin(2ωt)...
・■, which is expressed as the waveform diagram in Figure 3. In FIG. 3, the frequency change amount ΔΩa (broken line) corresponds to the voltage signal Ea, and the frequency change amount ΔΩb (−dot-dashed line) corresponds to the voltage signal Ea.
Corresponding to b, the frequency change amount ΔΩab (solid line) corresponds to the voltage signal Eab.

Furthermore, using the third power amplifier (32c), a voltage signal Ec (double-dashed line) as shown in FIG. 4 is generated, and this voltage signal Ec(t) is expressed as E c(t)−E If o-cos(3ωt)/3, then the voltage signal Eab actually applied to the crystal (31)
c (solid line) is obtained by combining each voltage signal Ea to Ec. At this time, a voltage signal Eab consisting of a function of time t
c(t) is E abc(t) = −Eo−cos(ωt)+E
o-eos(2ωt)/2-Eo-cos(3ωt)
/3 - Expressed as ■.

Therefore, the frequency change amount ΔΩabc(t) of the laser beam L2 after frequency sweeping in this case is ΔΩabc(t)−ΔΩa(t)+ΔΩb(t)+ΔΩ
c(t)=ωEO°5in(ωt) −ωEo−sin
(2ωt)+(11Eo-sin(3ωt)...■, and is expressed as the waveform diagram in Fig. 5. In Fig. 5, the frequency change amount ΔΩC (two-dot chain line) is the voltage signal E
The frequency change amount ΔΩabc (solid line) corresponds to the voltage signal E abc.

The laser beam L2 frequency-swept in this way is pumped by a laser amplification medium (52) excited by an amplification excitation source (52).
1), is amplified, and is emitted as the final laser beam L3. At this time, the excitation source for amplification (52) No. 1 is connected to the 17-4 Buddhist monk 17-4. Since the beam timing is adjusted by the delay circuit (60d), the laser amplification means (50) amplifies the nearly linear sweep portion of the laser beam L2 in synchronization with the sweep timing.

Also in this case, by adjusting the amplification timing, it is possible to obtain laser light L3 in which only the frequency change region from time t1 to t2 is amplified.

In this way, the crystal (
By applying a plurality of voltage signals Ea to Ec to 31), a sufficient frequency sweep amount can be secured with a relatively low voltage. Furthermore, by controlling the frequency sweep speed, it is possible to cover the light absorption spectrum of the irradiation target within a predetermined time and create an adiabatic inversion state in the energy state of the irradiation target.

In the above embodiment, a plurality of voltage signals Ea to Ec are applied to one crystal (31), but as shown in FIG. Crystals (31a) to (31c) are provided, and each crystal (31
Voltage signals Ea to Ec may be applied individually to a) to (31c). Here, three crystals (31a) to (31c
), but any number of crystals can be installed, not limited to three, and the power amplifiers and delay circuits can be added accordingly.

By using a plurality of crystals in this manner, each of the voltage signals Ea to Ec is applied in a distributed manner, so that the burden on each crystal (31a) to (31c) is reduced compared to the case of one crystal.

Moreover, since the frequency sweep amount by phase modulation of each crystal (31a) to (31c) is combined by the series arrangement, the final frequency sweep amount is the same as in the case of one crystal (31). Therefore, by applying the same voltage signal as in FIG. 2 or 4, the same frequency change amount ΔΩab or ΔΩabc as in FIG. 3 or 5 can be obtained, and the same effect as in the above embodiment can be obtained. play.

Furthermore, although a plurality of power amplifiers (32a) to (32c) were used as means for applying a plurality of voltage signals Ea to Ec, a plurality of control circuits were individually installed between a single power amplifier and the crystal. and send voltage signals Ea to E to each control circuit.
It may also include the waveform shaping function and timing control function of c.

Next, another embodiment of the present invention will be described in which individual voltage signals are generated from a single power amplifier via a plurality of control circuits.

FIG. 7 is a configuration diagram showing an embodiment of another invention of the present invention, in which the frequency sweeping means (30C) includes a plurality of crystals (31a) to (31c) arranged in series, and a plurality of crystals arranged in series. A single power amplifier (32) for applying a voltage signal to (31a) to (31c), and a single power amplifier (32) for applying a voltage signal to A plurality of control circuits (
33a) to (33c).

In this case, the power amplifier (32) is driven by the oscillator (40) and transmits the voltage signals Ea to Ec via the control circuits (33a) to (33c) to each crystal (31m) to (31c).
) are applied to each separately.

The control circuits (33a) to (33c) output voltage signals Ea to E
It has a waveform shaping function as well as a timing control function similar to that of a delay circuit.

In the configuration shown in FIG. 7 as well, by applying the voltage signal shown in FIG. 2 or 4, a frequency change amount ΔΩab or ΔΩabc similar to that shown in FIG. 3 or 5 can be obtained. Effects similar to those of the embodiment are achieved.

Also in this case, the number of crystals can be set arbitrarily, and it may be four or more, or one crystal (31) as shown in FIG. 1 may be used.

In each of the above embodiments, the laser amplification means (50)
Although the case where the laser oscillator (10) is arbitrarily selected is shown, for example, a high output laser beam L by pulse oscillation is provided.
1, it is not necessary to provide a laser amplification means (50), and the frequency-swept laser beam L2
may be output directly.

[Effects of the Invention] As described above, according to the present invention, a plurality of power amplifiers are provided for applying a plurality of voltage signals to the crystal, and relatively low voltage signals are synthesized and applied to the crystal. Therefore, a sufficient amount of frequency sweep of the laser light can be secured with a low voltage signal, and the light absorption spectrum of the irradiation target can be covered within a predetermined time by controlling the sweep time, and as a result, an adiabatic inversion state can be created. This has the effect of providing a laser frequency sweeping device that can perform

According to another invention of the present invention, a plurality of control circuits are provided to drive the crystal with a plurality of voltage signals, and relatively low voltage signals are synthesized and applied to the crystal. A laser frequency sweep device that can secure a sufficient amount of frequency sweep of the laser beam, cover the light absorption spectrum of the irradiation target within a predetermined time by controlling the sweep time, and as a result, create an adiabatic inversion state. There are benefits to be gained.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing one embodiment of the present invention, and Fig. 2 is a block diagram showing an embodiment of the present invention.
Figure 3 is a waveform diagram showing the voltage signal obtained by combining two voltage signals, Figure 3 is a waveform diagram showing the frequency change amount obtained by combining the frequency changes due to two voltage signals, and Figure 4 is
5 is a waveform diagram showing the amount of frequency change obtained by combining the amount of frequency change due to three voltage signals, and FIG. 6 is a waveform diagram showing the amount of frequency change obtained by combining the amount of frequency change due to three voltage signals. 7 is a block diagram showing an embodiment of another invention of the present invention; FIG. 8 is a block diagram showing a conventional laser frequency sweep device; FIG. 9 is a block diagram showing a voltage signal by the conventional device. FIG. 10 is a waveform diagram showing the amount of frequency change by a conventional device. (10)... Laser oscillator (30^) ~ (30C)... Frequency sweep means (31)
, (31a) to (31c)...Crystal (32), (3
2a) to (32c)...Power amplifiers (33a) to (3
3c)... Control circuit (60a) to (60d)... Delay circuit (timing control means) L1 to L3... Laser light E, Ea to Ec... Voltage signal. Indicates the same or equivalent part.

Claims (3)

[Claims] (1) including a laser oscillator that emits laser light with a narrow spectral width, and a crystal arranged so that the laser light passes through;
A laser frequency sweeping device comprising 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 timing control means for controlling the operation timing of the frequency sweeping means. , the frequency sweeping means includes a plurality of power amplifiers for applying a plurality of voltage signals to the crystal, and the timing control means individually controls operation timings of the plurality of power amplifiers. Laser frequency sweep device. (2) including a laser oscillator that emits laser light with a narrow spectral width, and a crystal arranged so that the laser light passes through;
and a frequency sweeping means for sweeping the frequency of the laser beam by phase modulation when a voltage signal is applied to the crystal, the frequency sweeping means applying a voltage signal to the crystal. A laser frequency sweeping device comprising: a power amplifier for applying voltage; and a plurality of control circuits inserted in parallel between the power amplifier and the crystal to generate a plurality of voltage signals. (3) The laser frequency sweeping device according to claim 1 or 2, wherein the frequency sweeping means includes a plurality of crystals arranged in series and to which a plurality of voltage signals are individually applied.