JPH0666501B2 - Multi-wavelength synchronous pulsed laser oscillation method - Google Patents

Description

The present invention relates to a method of oscillating a multi-wavelength synchronization pulsed laser.

[Conventional technology]

Figure 4 shows, for example, the magazine "OPTICS LETTERS" Vol.10, No12, P6.
FIG. 3 is a cross-sectional configuration diagram showing a conventional multi-wavelength synchronous CO ₂ laser described in 03 (1985), where (1) is a laser chamber (2) is a high voltage laser gain region, and (3) is a high voltage laser gain region ( Main electrode pair for generating excited discharge to form 2), (4) is a discharge excitation circuit for applying pulse high voltage to the main electrode pair (3), and causes discharge there, (5) is discharge A switching element for switching the excitation circuit (4), (6) a first low-pressure discharge tube, (7) a first low-voltage laser gain region for making the laser light into a single longitudinal mode, (8) Is a first low voltage electrode pair for generating an excitation discharge for forming a first low voltage laser gain region (7), (9) is a second low voltage discharge tube, (10) is a second low voltage laser gain region , (11) is the second low-voltage electrode pair, (12) is the first diffraction grating for selecting the wavelength of the laser light, (13)
Is the second diffraction grating, (14) is the first partial reflection mirror, (15) is the second partial reflection mirror, and (16) is the first diffraction grating (12) and the first partial reflection mirror. And the distance to the wavelength of laser light is λ / 10
The first PZT that can be changed strictly with an accuracy of about 0
Element, (17) is the second PZT element, (18) is the first diffraction grating (1
The oscillation optical axis (first oscillation optical axis) of the optical resonator composed of 2) and the first partial reflecting mirror (14), (19) is the second diffraction grating (1
The oscillation optical axis (second oscillation optical axis) of the optical resonator configured by 3) and the second partial reflection mirror (15), (20) is a total reflection mirror for bending the second oscillation optical axis, (21) is inserted in the first oscillation optical axis, the first aperture for making the laser light a single transverse mode, (22) is the second aperture, (23) is the first pulsed laser light, (24) is the second pulsed laser light.

Next, the operation will be described. The first low pressure discharge tube (6) and the second low pressure discharge tube (7) have an appropriate mixing ratio of CO ₂ , N ₂ and H.
_The laser gas composed of _e is flown at a low pressure of 50 torr or less. A pulse voltage is simultaneously applied to the first low-voltage electrode pair (8) and the second low-voltage electrode pair (9) to perform pulse discharge between the respective electrodes, and the first low-voltage laser gain region
(7) A second low-voltage laser gain region (10) is formed. At this time, by setting the angles of the first and second diffraction gratings (12) and (13) with respect to the first and second oscillation optical axes (18) and (19), the first and second low-pressure laser gains are set. CO _{2 in} each of the areas (7) and (10)
It is possible to selectively amplify only the light of a specific wavelength from the many oscillation lines existing in the laser. Further, the distance between the first and second diffraction gratings (12) and (13) and the first and second partial reflecting mirrors (14) and (15) is set to the first and second PZT elements (1
By adjusting 6) and 17), the light in a specific single longitudinal mode can be amplified by strictly changing it in the order of λ / 100. When the first and second low-voltage laser gains have risen sufficiently, a trigger is sent to the switching element (5) to operate the discharge excitation circuit (4). As a result, a pulsed high voltage is generated between the main electrode pair (3). The laser chamber (1) usually has atmospheric pressure or higher CO
The _2, N _2, H gas mixture has been placed consisting of _e, a high voltage applied to the main electrode pairs (3), a pulse discharge is performed, the high-pressure laser gain region (2) is formed. Here, only the light of a specific line generated in the first and second low-voltage laser gain regions (7) and (10) is amplified, and the light is amplified from the first and second partial reflecting mirrors (14) and (15), respectively. First and second pulsed laser light with different wavelengths and extremely high peak power (23), (2
4) is obtained. These laser lights are made into a single transverse mode by the first and second apertures (21) and (22) installed in the optical resonator, and the first and second low-voltage laser gain regions ( Due to the existence of 7) and (10), it is a single longitudinal mode, and the laser beam has extremely good beam quality.

Here, the energy level of the CO ₂ laser will be described. As shown in FIG. 5, the CO ₂ molecule has a symmetrical expansion and contraction ν ₁ , 2
It has three vibration modes of a degenerate bending ν ₂ and an asymmetric expansion and contraction ν ₃ , and its energy level is (ν ₁ , ν ₂ ⁿ ,
ν ₃ ). The laser oscillation is performed between two rotational levels included in two different vibration levels. Ordinary (00 ° 1) level is upper level, (10 ° 0) or (02
° 0) 10.4 μm band or 9.4 μm with lower level as lower level
Band laser oscillation is performed. Discharge selectively (0
N ₂ is usually added to the laser gas so that the excitation to the 0 ° 1) level takes place. As a result, about 80% of the discharge energy is used for excitation to the N ₂ V = 1 level, and this energy is rapidly transferred to the CO ₂ molecule due to vibration and vibrational transition to the (00 ° 1) level. The selective excitation of is realized.

As described above, the laser oscillation transition is a transition between vibration and rotation levels and is involved in laser oscillation (0
A large number of rotational levels exist in each vibration level of 0 ° 1), (10 ° 0), and (02 ° 0). This is shown in FIG. The thermal relaxation time of the rotational level is much shorter than the life of the vibrational level, and it can be considered that the thermal relaxation time normally has the Boltzmann distribution at the gas temperature T. Rotational quantum number J ′ of the upper level, “If the lower level is J, the only permissible transitions are J′-J = ± 1. At this time, the transition of -1 is p branch, +1. Is called the R branch, and J '= 2m-1 in the 10.4μm band.
Transition from J to 2m to 10p (2m), J '= 2m + 1 to J = 2m
The transition to is described as 10R (2m) (where m is a positive integer). Similarly, for the 9.4 μm band, it is described as 9p (2m) and 9R (2m). The number of lines capable of oscillating in the wavelength region of 9 to 11 μm is about 100, and one of them can be arbitrarily selected by the diffraction grating incorporated in the optical resonator as shown in the conventional example. .

Here, the gain of the laser in each oscillation line will be considered. The gain αδJ in a certain oscillation line is αδJ = σδJ · ΔNδJ (1) It is represented by. Here, σδJ: Stimulated emission cross section ΔNδJ: Inverted particle number density Nu: Particle number density of vibrational level in upper level Nl: Particle number density of vibrational level in lower level ΨJ: Distribution function of rotational level P, K , CHEO (Lasers, Vol.3, MARCEL DEKKER, In
c, New York, author of 1971), ΨJ is given by the following equation.

Here, B: rotation constant h: Planck's constant k: Boltzmann's constant C: speed of light T: gas temperature. From equation (3), the distribution of rotational levels in the upper level of CO ₂ is as shown in Fig. 7. However, T = 400 ° K. The rotational quantum number Jmax that gives the maximum number of particles at a certain temperature is given by the following equation (3).

For example, at T = 400 ° K, J'max = 19.

Due to the distribution of the rotational levels, the gain is completely different depending on the selected branch and J value even in the transition between certain vibrational levels.
Further, even in the 10.4 μm band in which the vibration levels of the lower levels are different, the gains are naturally different because the particle number densities distributed in the vibration levels are different. 10P under normal gas temperature conditions
The highest gain is obtained near the (20) line.

The laser device shown in the conventional example is used for the purpose of simultaneously irradiating two or more laser beams having different wavelengths in a certain application.

[Problems to be solved by the invention]

However, in the conventional multi-wavelength synchronous pulsed laser oscillation method, the gain is different depending on the oscillation wavelength, so that the time until the oscillation threshold is reached is different. Therefore, as shown in FIG. 8, the high gain line starts oscillation earlier in time, and a time delay Δt of oscillation occurs between the high gain line and the low gain line,
There was a problem that the two-wavelength synchronous oscillation was not possible. In order to correct this, the gas pressure in the low pressure gain region is controlled, and thereby the rise time of the laser light in the high voltage gain portion is controlled. However, with this method, the gas pressure in the low-pressure gain section must be controlled very strictly, and the time delay cannot be corrected when the gains of the two laser beams are extremely different. It was

The present invention has been made to solve the above problems, and an object thereof is to realize a multi-wavelength synchronous pulse laser oscillation capable of simultaneous oscillation in different oscillation lines.

[Means for solving problems]

In the multi-wavelength synchronous pulsed laser oscillation method according to the present invention, the laser chamber containing the high-pressure laser gas is independent for each optical resonator, and the laser gas mixing ratio in the high-voltage laser gain region is independently controlled. .

[Action]

In the multi-wavelength synchronous pulsed laser oscillation method according to the present invention, the laser gain at each oscillation wavelength can be greatly adjusted by independently controlling the gas mixture ratio of the high-voltage laser gain region in each optical resonator. It is possible to adjust the time until the oscillation between wavelengths greatly different from each other is reached.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
In the figure, (25) is the second laser chamber, (26) is the second high voltage laser gain region, (27) is the second main electrode pair, (28)
Is a second discharge excitation circuit, (29) is a first laser gas mixing ratio adjusting mechanism, and (30) is a second laser gas mixing ratio adjusting mechanism.

Next, the operation of the above embodiment will be described. The operations of the first and second low-pressure discharge tubes (6) and (9) are the same as in the conventional example. When the first and second low-voltage laser gains have risen sufficiently, a trigger is sent to the switching element (5) to simultaneously operate the first discharge excitation circuit (4) and the second discharge excitation circuit (28). . As a result, a pulse high voltage is generated between the first main electrode pair (3) and the second main electrode pair (27).

First Laser Chamber (1), Second Laser Chamber
(25) a gas mixture consisting of CO _{2, N 2,} H _e of different mixing ratios in the first, second laser gas mixture ratio adjusting mechanism (2
According to 9) and (30), the pressure is around atmospheric pressure or higher. The first main electrode pair by applying high voltage
(3) A main discharge occurs between the second main electrode pair (27). At this time, since the main discharges performed at the two places are operated by one switching element (5), there is no jitter associated with the switching, and the discharges are almost simultaneous in time. In the first high voltage laser gain region (2) and the second high voltage laser gain region (26) formed by these main discharges, the first and second low voltage laser gain regions (7), (10) Only the light of a specific line generated in 1 is amplified, and the first and second partial reflectors (1
From 4) and 15), it is possible to obtain the first and second pulsed laser light (23) and (24) having different peak wavelengths and extremely high peak power.

First Laser Chamber (1), Second Laser Chamber
The gas mixture ratio in (25) is CO ₂ , N ₂ on the high gain line side.
It is set to reduce the absolute amount of. At this time, since the number density Nu of particles excited in the upper level (00 ° 1) of the laser decreases, the inverted particle number density ΔNδJ decreases and the gain in that line is decreased. As a result, the rise time of the gain until the oscillation threshold is reached is increased, and simultaneous oscillation with the low gain line is realized as shown in FIG. FIG. 3 is a block diagram showing a laser gas mixture ratio control mechanism for automatically controlling the gas mixture ratio in the laser chamber. In the figure, (31) and (32) are the first and second lasers. An optical sensor that detects the light (23) (24), (33) is a digitizer that measures the times t ₁ and t ₂ showing the peak values of the two laser lights (23) (24), and (34) is t ₁ and t _A comparator for measuring the difference Δt between ₂ and (35) is a Δt obtained by the comparator (34) based on the data in the memory (36) which stores the relationship between the gas amount and Δt.
An arithmetic circuit for determining the amount of gas with respect to the value of (37) is a gas control circuit for driving the gas valve (38) based on the data obtained by the arithmetic circuit (35).

In the above-mentioned embodiment, the simultaneous oscillation of two wavelengths is explained, but main discharge may occur simultaneously in three or more independent high voltage laser chambers. At this time, gas is generated in each chamber as in the above-mentioned embodiment. By controlling the mixing ratio, simultaneous oscillation of three or more wavelengths is realized. In the above embodiment has been described for the case of three mixed gas of _{CO 2,} N 2, _{H e} as the laser gas, _CO in order to suppress the CO ₂ gas is dissociated by discharge, H _{2, H} 2 O, for the case where gas X _e or the like is also added, it is needless to say that acts effectively.

Further, in the above-mentioned embodiment, the case of pulse discharge as the excitation discharge in the low-voltage laser gain region has been described, but continuous discharge may be used.

〔The invention's effect〕

As described above, according to the present invention, the laser chamber containing the high-pressure laser gas is independent for each optical resonator,
Since the laser gas mixing ratio in the high-voltage laser gain region is controlled independently, simultaneous oscillation in different oscillation lines is possible, and there is an effect that a stable multi-wavelength synchronous pulse laser can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional configuration diagram showing a multi-wavelength synchronous pulse laser according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing a temporal relationship between two laser beams according to an embodiment of the present invention. Three
FIG. 4 is a block diagram showing a laser gas mixing ratio control mechanism according to another embodiment of the present invention, and FIG. 4 is a conventional multi-wavelength synchronization type C
O ₂ cross-sectional view showing a laser, FIG. 5 is an explanatory view illustrating the energy level of the CO ₂ laser, Fig. 6 is an explanatory view for explaining the oscillation lines of the CO ₂ laser, Fig. 7 is rotational levels of FIG. 8 is a distribution diagram showing a distribution, and FIG. 8 is a waveform diagram showing a temporal relationship between two laser lights obtained by the conventional multi-wavelength synchronous pulsed laser oscillation method. In the figure, (1) is the first laser chamber, (2) is the first high-voltage laser gain region, (7) is the first low-voltage laser gain region, (7) is the first low-voltage laser gain region, (10) is the second low-voltage laser gain region, (12) is the first diffraction grating, (13) is the second diffraction grating, (14) is the first partial reflecting mirror, and (15) is the first Second partial reflection mirror, (23) a first laser beam, (24) a second laser beam, (25) a second laser chamber, (26) a second high-voltage laser gain region, ( 29) is a first laser gas mixture ratio control mechanism, and (30) is a second laser gas mixture ratio control mechanism. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Namba 2-1, Hirosawa, Wako-shi, Saitama, RIKEN (72) Inventor Yukio Sato 8-1-1 Tsukaguchihonmachi, Amagasaki-shi, Hyogo Sanryo Electric Co., Ltd. Company Applied Equipment Laboratory (72) Inventor Hideki Kita 8-1-1 Tsukaguchihonmachi, Amagasaki City, Hyogo Sanryo Electric Co., Ltd. Itami Works

Claims (3)

[Claims] 1. A laser chamber filled with a laser gas having a pressure of about atmospheric pressure or higher, a high-voltage laser gain region formed by pulse discharge performed in the laser chamber, and a laser gas of 50 torr or less. A plurality of low-voltage discharge tubes, a low-voltage laser gain region formed by continuous or pulse discharge performed in the low-pressure discharge tube, and a high-voltage laser gain region and the low-voltage laser gain region so as to face each other. In a multi-wavelength synchronous pulsed laser oscillation method comprising a plurality of sets of optical resonators composed of a partially reflecting mirror and a diffraction grating installed, and extracting laser light of a single longitudinal mode of different wavelengths from each of the optical resonators. The laser chamber has a plurality of independent high-pressure laser gain regions having different laser gas mixing ratios for each optical resonator. Laser Chillan consists bar, by adjusting the gas mixing ratio of the high-pressure laser gain region, multi-wavelength-locked pulsed laser oscillator wherein the taking time synchronization between different oscillation wavelengths. 2. A laser gas CO _2, N ₂ and multi-wavelength-locked pulsed laser oscillator method of Claims preceding claim, which is a 3-component mixture gas of H _e. 3. The multi-wavelength synchronous pulsed laser oscillation method according to claim 1 or ₂ , wherein the laser gas contains CO, H ₂ , H ₂ O, or X _e .