JPH04255283A - Two-wavelength oscillation q switch co2 laser device - Google Patents

Abstract

PURPOSE:To obtain Q switch pulse CO2 laser rays which are coaxially oscillated in two wavelengths in the same discharge excitation space using a single CO2 laser discharge tube. CONSTITUTION:In a Q switch CO2 laser device, a two-color coating mirror 3 which transmits laser rays of first wavelength but reflects laser rays of second wavelength is inserted in a laser resonator which is composed of a total reflection mirror 1 and a partial reflection mirror 2 (output mirror) and oscillates in first wavelength, and a resonator of second wavelength is composed of the mirror 3 concerned and the mirror 2 of the resonator of first frequency, whereby pulse laser rays coaxially oscillated in two wavelengths in the same excitation space can be obtained. Simultaneous irradiation with two-wavelength pulse laser ray required in a photochemical process such as a laser isotope separation process can be realized through a simple method by the use of a single laser oscillator.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention applies pulsed CO2 coaxially oscillated at two wavelengths from the same excitation space, which is required in photochemistry using a laser, typified by laser isotope separation.
The present invention relates to a Q-switched CO2 laser device for obtaining laser light.

0002

BACKGROUND OF THE INVENTION With the dramatic progress of CO2 laser technology in recent years, its application fields are not limited to conventional simple material processing, but are expanding into new fields. Typical examples include light sources used in photochemical processes such as laser isotope separation using pulsed CO2 laser light, and light sources for optical excitation of far-infrared lasers. When applying CO2 lasers to such fields, an infrared multiphoton excitation process is generally used, so the target substance is often molecules, and the laser has a high peak output. A pulse waveform is required. Furthermore, the gap between the excited levels of a substance becomes narrower as it goes to higher excited levels, so
When performing infrared multiphoton excitation, it is known that the excitation efficiency is significantly improved by excitation with multiple wavelengths including the resonant wavelength rather than by resonant excitation with a single wavelength.

0003

[Problems to be Solved by the Invention] Conventionally, as a CO2 laser compatible with such applications, a pulsed TEA (Transversely Ex
Cited Atmospberic Pressur
e) There is a CO2 laser. As a method to obtain oscillation pulses at multiple wavelengths from a single TEA laser oscillator, Sov
．． J. Quantum Electronics Magazine V
ol. 15 No. 5 p689-691 (1985
), a method has been proposed in which a discharge excitation space is divided into three locations and each space is caused to resonate at different wavelengths using a diffraction grating to obtain oscillation pulses at three wavelengths. TEA
In a laser, since the laser medium is at near atmospheric pressure, the probability of collision between the laser media is high, and rotational level relaxation within the laser excitation level and lower level occurs rapidly due to this, and the time constant is It is typically 1/10 or less of the laser pulse width. Therefore, when trying to obtain multiple wavelength oscillation from the same discharge excitation space using a TEA laser,
Similar to the phenomenon in dye lasers, there is a problem in that competition occurs between the respective oscillation wavelengths and the output becomes unstable. In the above example, in order to avoid such problems, separate discharge excitation spaces are used for each oscillation wavelength, but in this case, it is impossible to effectively use the entire discharge excitation space. Since this is not possible, there are problems in that the oscillation efficiency decreases and the oscillation optical axes are not the same. JP-A-1-96977 discloses a multi-wavelength synchronous TEACO2 pulse laser oscillation method. This method aligns the oscillation timing of multiple wavelength pulses by placing laser gases with different compositions in multiple laser excitation chambers that are synchronized by the same switching element, and is effective in obtaining laser pulses of multiple wavelengths at the same timing. However, it requires a plurality of laser excitation chambers, which increases the size of the device, and there are problems in that coaxial laser oscillation light cannot be obtained.

[0004] As a configuration for obtaining pulse oscillation light of multiple wavelengths from a Q-switch CO2 laser, J. Phys. Che
m. Magazine Vol. 18 No. 1 p86-94 (198
In 5), a configuration has been proposed in which a rotating mirror is used as a Q-switch device and is shared by two resonators. With this method, it is possible to obtain temporally synchronized pulsed light with multiple wavelengths, but it requires multiple discharge tubes, which increases the size of the device, and because two resonators share one rotating mirror. , the optical axis adjustment becomes extremely complicated, making it difficult to ensure long-term oscillation stability, and the oscillation pulses are obtained from separate resonators, so they cannot be obtained as coaxial pulsed laser light. There is.

An object of the present invention is to increase the size of the device in order to coaxially obtain pulsed CO2 laser light of two wavelengths with high peak output required in the photochemical field such as laser isotope separation from the same space. With a simple configuration without becoming complicated,
An object of the present invention is to provide a Q-switched CO2 laser device that is inexpensive and has high reliability that can withstand long-term stable operation.

[0006]

[Means for Solving the Problems] The present invention provides a device for generating pulsed laser light from a CO2 laser using a Q-switch, in which a first wavelength light beam is composed of an output mirror consisting of a total reflection mirror and a partial reflection mirror. A mirror coated with a dichroic coating having wavelength selectivity that transmits a first wavelength and reflects a second wavelength is inserted into a laser resonator that oscillates at This is a Q-switched CO2 laser device that can extract pulsed laser light that coaxially oscillates at two wavelengths from the same excitation space by configuring a second wavelength resonator with an output mirror.

[0007]

[Operation] The present invention will be explained in detail below. Figure 3 shows CO2
FIG. 2 is an explanatory diagram showing only the laser excitation level and lower level in a simplified manner to explain the energy level of the laser. The CO2 molecule has three vibrational modes: symmetric stretching mode n1, bending mode n2, and asymmetric stretching mode n3, and its energy level is (n1 n m2 n
3). Oscillation in the 10.4 μm band and 9.4 μm band, which are typical oscillation lines of CO2 laser, is (0
The rotational level among the 00 1) levels is set as the upper level, and laser oscillation is obtained as a transition to the rotational levels among the (1 000) and (0 20 0) levels, respectively. Since each vibrational level has a large number of rotational levels, a large number of oscillation lines exist. Here, the relaxation speed of the rotational level is considerably faster than the relaxation speed of the vibrational level, and increases in proportion to the pressure of the laser gas. Therefore, in a laser that operates near atmospheric pressure, such as a TEA laser, relaxation between rotational levels occurs at the rise of the laser pulse, which results in efficient operation when oscillating at a single wavelength, but from the same space. If you try to obtain transitions of multiple wavelengths, competition will occur between each transition, making oscillation unstable. However, the laser gas pressure used for Q-switch oscillation is about several tens of torr. If you try to perform continuous wave operation even under pressure conditions of this level, competition between multiple transitions similar to the above will occur.
Typical Q-switch pulse width (100-300nsec
), rotational level relaxation does not complete completely, making it possible to stably extract a plurality of wavelengths due to different transitions from the same space.

FIG. 4 is a schematic diagram for explaining the configuration of the present invention. In the same figure (a), the first wavelength (for example, 9.4μ
This is a configuration diagram of a resonator for obtaining oscillation at one wavelength in the m band.The diffraction grating 1 operates as a total reflection mirror for selecting the wavelength, and the output mirror 2 consisting of a partial reflection mirror selects the first wavelength. The oscillation laser beam 9 is extracted. Same figure (b)
is the second wavelength (for example, one wavelength in the 10.4 μm band)
This is a configuration diagram of a resonator for obtaining oscillation with a mirror 3 coated with a dichroic coating having wavelength selectivity that transmits a first wavelength and reflects a second wavelength as a total reflection mirror for the second wavelength. The oscillation laser beam 10 of the second wavelength is extracted from the output mirror 2 which is a partially reflecting mirror. Figure (c) is a schematic diagram illustrating the configuration of the present invention by combining (a) and (b). In the resonance of the first wavelength, mirror 3 with dichroic coating is inserted compared to that shown in FIG.
Since the reflectance for the first wavelength is suppressed as much as possible, oscillation is maintained with only a slight loss. The resonance of the second wavelength is exactly the same as the resonator configuration shown in FIG. 3(b), and as described above, there is no competition with the first wavelength, so stable oscillation can be obtained. As described above, since the resonant systems for the two wavelengths share the same output mirror 2, it is possible to obtain pulsed laser beams 9 and 10 coaxially oscillated at two wavelengths from the same excitation space. .

Next, dichroic mirror coating will be explained. Figure 5 shows that by coating the ZnSe substrate, it has a high reflectance near 10.6 μm and a thickness of 9.5 μm.
This figure shows the calculated value of the wavelength dependence of the light transmittance of a mirror designed to achieve high transmittance in the vicinity. As is clear from the figure, at 9.5 μm, which corresponds to the first wavelength, 99
It is possible to achieve a transmittance of 90% or more, and a reflectance of 90% or more at 10.6 μm corresponding to the second wavelength. In this design, the reflectance for the second wavelength was limited to this level. This is 10% from the dichroic mirror 3 to the diffraction grating 1 in the oscillation of the second wavelength.
This means that there is the following loss, but this loss is sufficiently low compared to the transmittance of the output mirror 2 (30% to 70%) in a general CO2 laser, so it is a factor that inhibits the oscillation of the second wavelength. Must not be.

Although FIG. 4 shows an example in which the diffraction grating 1 is used as a total reflection mirror for the first wavelength, the transmission characteristics of the dichroic mirror 3 in the vicinity of the first wavelength are as shown in FIG. In steep cases, it is also possible to replace it with a simple total reflection mirror without wavelength selectivity, such as a metal mirror or a coated mirror. In addition, in FIG. 5, the two wavelengths are 10.6 μm and 9.6 μm.
Although an example has been shown in which a value of 5 μm is selected, it goes without saying that any combination can be used within the range where dichroic mirror coating can be realized. As a Q-switch device, a rotary chopper type is most preferable because it has a fast Q-switching speed to shorten the laser pulse width as much as possible, is highly durable, and can ensure long-term stability of resonator alignment. Elements that utilize electro-optic effects such as commonly used CdTe,
It may be either a rotating mirror or a Fabry-Perot etalon. Furthermore, the discharge excitation source may be either a commonly used DC power supply or a high frequency AC power supply, and the discharge form is preferably a pulse discharge synchronized with the Q switch from the viewpoint of shortening the Q switch pulse width. Continuous wave discharge may also be used.

[0011]

Embodiment FIG. 1 shows an embodiment of a two-wavelength oscillation Q-switched CO2 laser device according to the present invention. discharge tube 4
is a high-speed axial flow high-frequency AC discharge type, and C
A total pressure of 50 ton consisting of a mixed gas of O2, N2, and He
rr laser gas is circulated in the laser optical axis direction at a linear velocity of 200 m/sec by a roots blower (not shown). The inner diameter of the discharge tube is 18 mm, glow discharge occurs in a direction perpendicular to the optical axis, and the maximum value of discharge injection power is 1.
0kW, maximum repetition frequency of discharge pulse modulation is 10k
It is Hz. The two condensing lenses 6 are ZnSe lenses with a focal length of 200 mm and coated with a broadband anti-reflection coating in the wavelength band of 10 μm, and are installed under confocal conditions to operate as a telescope. The rotary chopper 7 is a Q-switch device that has 12 notches with a width of 2 mm on the circumference of a disc with a diameter of 160 mm, and has a maximum rotation speed of 70,000 rpm.
It rotates at m and is installed at the confocal position of the telescope. The ZnSe all-transmissive window 5 is a window material provided to block the low-pressure laser gas from the atmosphere, and is coated with a broadband anti-reflection coating in the wavelength band of 10 μm. The diffraction grating 1 is blazed at 150 gratings/mm, and is adjusted to resonate with the output mirror 2 at a wavelength of 9.54 μm (9P(18)). The output mirror 2 has a wavelength of 9.
It has a reflectance of 35% at both 54 μm and 10.6 μm. The dichroic mirror 3 is a ZnSe mirror manufactured based on the design shown in FIG.
The transmittance at μm is 95%, and the reflectance at a wavelength of 10.6 μm is 92%. The dichroic mirror 3 is installed on the end face of the discharge tube 4 and also serves as a window material to block the low-pressure laser gas from the atmosphere. tuned to resonate. As a result of performing Q-switch oscillation at a pulse repetition frequency of 10kHz in the above configuration,
Laser pulses with approximately the same output ratio were stably obtained with the two oscillation lines of 9P (18) and 10P (20) with a total energy of 40 mJ and a pulse width at half maximum of 100 nsec. FIG. 2 shows another embodiment of the two-wavelength oscillation Q-switched CO2 laser device according to the present invention. In this embodiment, the diffraction grating 1 in FIG. 1 is replaced with a copper mirror 8 coated with gold, and the other configurations are exactly the same as in FIG. 1. As a result of performing Q-switch oscillation at a pulse repetition frequency of 10 kHz with this configuration, the first wavelength is 9P (20), (9.55 μm), which has the highest transition probability in the 9P branch.
), but as a result of eliminating the loss due to the diffraction grating, the laser pulse with almost the same output ratio in the two oscillation lines of 9P (20) and 10P (20) is stable, with a total energy of 50 mJ and a pulse half It was obtained with a value width of 100 nsec.

0012

Effects of the Invention As explained above, according to the two-wavelength oscillation Q-switched CO2 laser device of the present invention, a single laser discharge tube is used and a simple configuration is used to generate two wavelengths of CO2.
Since laser pulses can be extracted coaxially using the same discharge excitation space, there is an advantage that an oscillation device with high performance and high reliability can be constructed at low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of a two-wavelength oscillation Q-switched CO2 laser device of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining the energy level of a CO2 laser.

FIG. 4 is a schematic diagram for explaining the configuration of the present invention (a)
is a resonator configuration diagram for oscillation of the first wavelength, (b) is a resonator configuration diagram for oscillation of the second wavelength, and (c) is a configuration diagram of the resonator for oscillation of the second wavelength.
, (b) is shown.

FIG. 5 is an explanatory diagram showing the results of calculating the wavelength dependence of the light transmittance of a dichroic coated mirror.

[Explanation of symbols]

1 Diffraction grating 2 Output mirror 3 Dichroic coating mirror 4 Discharge tube 5 Fully transparent window 6. Condensing lens 7 Rotating chopper 8 Total reflection metal mirror 9 Laser beam of first wavelength

Claims (5)

[Claims] Claim 1: A device for generating pulsed laser light from a CO2 laser using a Q-switch, in which a laser resonator that oscillates at a first wavelength is comprised of an output mirror consisting of a total reflection mirror and a partial reflection mirror. , a mirror coated with a dichroic coating having wavelength selectivity that transmits a first wavelength and reflects a second wavelength is inserted, and the output mirror of the resonator for the first wavelength transmits the second wavelength. A dual-wavelength oscillation Q-switched CO2 laser device characterized in that it obtains pulsed laser light coaxially oscillated at two wavelengths from the same excitation space by configuring a resonator. 2. The two-wavelength oscillation Q-switch CO2 according to claim 1, wherein the total reflection mirror of the first wavelength resonator is a diffraction grating.
laser equipment. 3. The two-wavelength oscillation Q-switched CO2 laser device according to claim 1, wherein the total reflection mirror of the first wavelength resonator is a metal mirror or a coated mirror. 4. The Q-switch device placed in the laser resonator is any one of a rotating chopper, an electro-optical element, a rotating mirror, and a Fabry-Perot etalon.
Wavelength oscillation Q-switch CO2 laser device. 5. The two-wavelength oscillation Q-switch according to claim 1, wherein the power source used to excite the discharge of the CO2 laser is a DC or AC power source, and the discharge form is either continuous wave or pulsed discharge synchronized with the Q-switch. CO2 laser equipment.