JP2992548B2 - Gas phase photochemical reactor using laser light - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactor for performing a photochemical reaction such as isotope separation using a laser beam, and in particular, most of the laser energy that can be extracted from a laser medium is effectively used for the photochemical reaction. The present invention relates to a gas phase photochemical reaction device that can be used.

[0002]

2. Description of the Related Art In recent years, the increase in output power and the diversification of oscillation wavelengths in laser technology have promoted research for utilizing lasers for photochemical reactions. The most typical example of the application of lasers to photochemical reactions is the isotope separation and enrichment technology of various elements ranging from hydrogen to uranium, which utilizes the isotope shift of the light absorption characteristics of the raw material to achieve the desired effect. This is because the chemical reaction of only the substance containing the isotope is promoted. Conventionally, various methods and apparatuses have been proposed for such isotope separation / concentration reactions using a laser beam. For example, the apparatus disclosed in FIG. 1 of Japanese Patent Application Laid-Open No. Sho 60-132,629 discloses a method in which a pulsed carbon dioxide laser beam is condensed by a long focal length lens and introduced into a reactor. A reaction is performed. In a photochemical reaction using such infrared multiphoton absorption, the reaction efficiency generally increases exponentially with increasing laser energy density up to a certain value, and the reaction efficiency is saturated at higher values. Fluence exists. For this reason, the laser beam is converged by a focusing lens having a focal length at which the critical fluence is obtained at the focused position, and the reaction proceeds near the focal point. Therefore, in such a reactor, the laser power is effectively used only in a part of the reactor, and the laser energy is absorbed without contributing to the reaction in the region where the critical fluence is less than the inside of the reactor. Further, since the remaining energy is dissipated from the exit end of the reactor, there is a problem that only a few to 20% of the laser power actually output from the laser oscillator is effectively used for the chemical reaction.

In the photochemical reaction process using a laser beam, the ratio of the laser is the highest in both the initial cost and the running cost. In order to realize a low-cost laser photochemical reaction process, the laser power must be reduced. Effective utilization technology is an essential requirement. In order to cope with such a problem, a series multi-stage light condensing system as shown in FIG. 3 of Japanese Patent Application Laid-Open No. 59-123,517 has been proposed. However, in this method, as the number of condensing stages increases, the utilization rate of the laser power increases as compared with the above method, but the reactor becomes enormous in length, and it is difficult to secure the stability of the optical axis. In addition, there are problems such as a large loss of laser energy that does not contribute to the reaction due to absorption of the raw material before and after the focal point of each stage. In order to cope with the former problem, as a method in which the length of the reactor is short and the laser power can be used effectively, a multiple reflection mirror pair as shown in FIG. 1 of JP-A-54-12290 is used. There is an example of a reactor provided with. In this case, the superposition is repeated without focusing in the multiple reflection of the beam. Therefore, when the required critical fluence is a low value of about 1 J / cm ² , this is a very effective method.
For example, when 5 to 6 J / cm ² is required, it is difficult to realize this over the entire overlapping area. Furthermore,
Since the surface shape of the reflecting mirror becomes complicated and a reaction occurs near the reflecting mirror, the surface of the reflecting mirror is stained by a reaction product, and there is a problem that a stable reaction cannot be realized for a long time.

As a method of realizing reflection and superimposition using a simple optical system, the applicants of the present invention have made the focusing positions of the forward and backward beams coincide with each other, and superimpose two or more beams near the focal position. Japanese Patent Application Laid-Open No. 2-251,227 discloses an example of two-pass superposition, and Japanese Patent Application No. 2-126,836 discloses an example of multi-pass reflection superposition. In these methods, any desired fluence can be realized by appropriately selecting the curvature of the reflecting mirror, and the reflected beam optical axis and the laser oscillation optical axis are set so as to finally coincide with each other. Superimposition beyond the beam is reliably realized. However, in these methods, when the number of reflection paths is increased to improve the efficiency of using laser energy and the laser propagation distance is increased, there is a problem that it is difficult to maintain the alignment of the reflecting mirror stably.
Furthermore, in the multiple reflection system, the laser convergence profile changes gradually due to the beam divergence caused by diffraction in the laser oscillator and the self-focusing / diffusion effect of the laser beam due to the reactant, so the number of reflection paths naturally has a maximum value. And it was not possible to use all the energy extracted from the laser oscillator for the reaction. In addition, the residual laser energy that did not contribute to the reaction returns to the laser oscillator side, but since the spatial mode of this reflected beam generally does not match that of the laser oscillator, even if the reflected beam returns inside the laser oscillator, it will cause diffraction loss. Lost. In a severe case, there is a possibility that optical components related to the laser oscillator may be damaged.

To cope with such a problem, US Pat. No. 4,072,590 discloses a laser beam in which a laser resonator is constituted by a total reflection mirror at both ends and a reaction vessel is inserted into the laser resonator. Discloses an isotope separation method. In this method, all the energy that can be extracted from the laser medium is confined in the resonator, so that the energy can be effectively coupled to the reaction medium. However, in this method, the laser resonator is simply composed of only two total reflection mirrors, and the reaction vessel is inserted between them. Therefore, once the conditions of the laser resonator are determined, the laser cavity is not used. The laser energy density cannot be changed.
Here, in the laser photochemical reaction, an energy density near the critical fluence is required as described above, but this value is generally in the range of several to several tens J / cm ² . However, the breakdown threshold of a multilayer coating generally used for a mirror for a laser resonator is about 1 J / cm ² , and a much higher fluence is required in a reaction vessel than the laser energy density on a total reflection mirror. Will be. In order to satisfy such a condition, it is necessary to use a resonator mirror having a considerably small radius of curvature. In this case, however, the beam mode in the laser medium changes at the same time. It becomes difficult to remove.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of inserting a reaction vessel into a resonator constituted by two pairs of total reflection mirrors. By realizing a simple device that can obtain high laser light intensity in the reaction vessel without deteriorating the extraction efficiency, the photochemical reaction efficiency for the energy that can be extracted from the laser medium will be significantly higher than that of the conventional method. It is an object of the present invention to provide a reactor which can realize an improved and inexpensive process.

[0007]

According to the present invention, a laser beam is introduced into a reaction region in a reaction vessel in which a gaseous source material is present, and a desired chemical reaction is performed using the light absorption characteristics of the source material. In the device, the laser resonator is composed of a total reflection mirror pair,
In a gas-phase photochemical reaction device using laser light that inserts a reaction vessel into a laser resonator, a telescope consisting of a pair of focusing optics is provided inside the laser resonator, and the reaction vessel is placed at the laser focusing position between them. A gas-phase photochemical reaction apparatus using laser light, which is installed and controls the laser light intensity in the reaction vessel by changing the focal length of the telescope optical system, which can be extracted from the laser medium. An object of the present invention is to provide a device capable of effectively utilizing almost all of laser energy for a photochemical reaction.

[0008]

The present invention will be described below in detail. FIG. 2 shows an example of the arrangement of optical components according to the present invention. A laser resonator for laser medium consists of a total reflection mirror M ₂ which is installed in a total reflection mirror M ₁ and therewith a position facing consisting of Bragg gratings disposed Ritorou type to select the lasing wavelength. The total transmission window W is a window that shuts off the gas laser medium and the atmosphere and allows the entire laser beam to pass through. The lenses L ₁ and L ₂ constitute a telescope, and their focal length is determined from a fluence value required in a photochemical reaction. The reaction vessel 2 is installed at a point where a desired fluence value is obtained between telescopes. In the above configuration, the stimulated emission light extracted from the laser medium resonates between the total reflection mirror pair M ₁ and M ₂ , leading to laser oscillation. Here, the threshold condition for laser oscillation is that the gain obtained from the laser medium during one round trip of the laser light in the resonator exceeds other losses. The loss due to the reactant varies depending on the laser wavelength, the pressure of the reactant gas, and the type, but the loss in one pass is at most a few percent at most. On the other hand, considering that the transmittance of the output mirror of a general laser oscillator is at least 10% or more, the laser gain in one round trip in the resonator is 1 / 0.9 or more. In the configuration of the present invention, the output mirror is replaced by a total reflection mirror (transmittance ０0%), and instead of reducing this loss, the above-described loss due to the reactant is introduced, which is compared with the laser gain. Therefore, the laser oscillation threshold condition is sufficiently satisfied. Here, the non-reflective coating is applied to the laser oscillation wavelength of the total transmission window W and the telescope lenses L ₁ and L ₂ existing in the laser resonator.
Also, since the laser light introduction window of the reaction vessel 2 is set at a Brewster angle to prevent reflection loss, the loss in the laser resonator is caused by the reflection loss of the total reflection mirrors M ₁ and M ₂ and the reaction medium. Only the energy loss absorbed by the A desired laser fluence is obtained in the reaction vessel 2 by the telescope, and all of the energy extracted from the laser medium, except for the component lost by the total reflection mirror, is injected into the reaction medium. The photochemical reaction efficiency per laser pulse can be dramatically improved. FIG. 3 shows an example of the arrangement of another optical component based on the same principle as that of FIG. 2, in which the telescope lenses L ₁ and L ₂ are changed to total reflection spherical mirrors M ₃ and M _4. Yes, the operation is exactly the same as in FIG.

Next, a method for realizing a desired laser fluence in the reaction vessel without changing the spatial mode of the laser beam in the original laser oscillator by inserting a telescope will be described. FIG. 4 schematically shows one form of the original laser oscillator, and the partially transmitting mirror OC operates as a laser output mirror. FIG. 5 shows that in the optical component arrangement of FIG. 4, l ₁ = 2800 mm R ₁ = ∞ (planar), R ₂ = 15000 mm (concave), R
FIG. 6 shows the results of analyzing the spatial propagation profile of a Gaussian beam in a resonator by the ray tracing method using an ABCD matrix under the condition of ₃ = ∞ (plane). In order to extract laser energy from the laser medium most efficiently, it is necessary to match the space of the excited laser medium in the resonator with the spatial mode of the laser beam that can be generated in the resonator.

In the following description, the optical component arrangement of FIG. 4 will be considered as an originally optimized laser resonator, and the discussion will proceed assuming that the spatial profile of FIG. 5 matches the spatial profile of the excitation medium. In the following, since the comparison of the spatial profiles is the main point, when the analysis results are shown in the format of FIG. 5, both the vertical and horizontal axes are represented by the same scale.

FIG. 6 shows that in the optical component arrangement of FIG. 2, l ₁ = 2800 mm, l ₂ = 500 mm, and l ₃ = 159.
0 mm, l ₄ = 210 mm f ₁ = 800 mm, f ₂ = 800 mm R ₁ = R ₂ = R ₃ = ∞ (flat), R ₄ = 15000 m
In the condition of m (concave surface), when the total reflection mirror pair M ₁ , M ₂ is considered as a mirror for a laser resonator, a ray tracing result of a spatial propagation profile of a Gaussian beam generated in the resonator is shown. is there. Spatial profile of the laser beam between the contrasting this figure and FIG. 5 and the total reflection mirror M ₁ to the total transmission window W are almost identical both, and the laser beam is condensed in between the telescope lenses L _1, L ₂ It is shown that the laser power density is increased.

FIG. 7 shows that, in the optical component arrangement of FIG. 2, l ₁ = 2800 mm, l ₂ = 500 mm, and l ₃ = 308.
0 mm, l ₄ = 520 mm f ₁ = 1600 mm, f ₂ = 1600 mm R ₁ = R ₂ = R ₃ = ∞ (flat), R ₄ = 15000 m
The condition of m (concave surface), that is, the focal lengths of the telescope lenses L ₁ and L ₂ are respectively doubled and the distances l ₃ and l ₄ are increased as compared with FIG. It shows the result of ray tracing. As in FIG.
Spatial profile of the laser beam between the total reflection mirror M ₁ to the total transmission window W is substantially the same as that of FIG. 5, and from a comparison with the results of Figure 6, the focused beam diameter of between telescope lens Since the laser power density is approximately doubled, it can be seen that the laser power density is reduced to approximately 1/4. The examples described above merely show the analysis results under the two conditions as the focal length of the telescope. However, since these focal lengths can be changed arbitrarily, according to the present invention, a focal length appropriately selected according to the required fluence is provided in the laser resonator constituted by the total reflection mirror pair M ₁ and M ₂ . It can be seen that by inserting a telescope, an arbitrary laser power density can be realized between telescopes without breaking the matching condition between the laser beam spatial profile and the spatial profile of the laser excitation medium.

Next, the difference between the prior art and the present invention will be described. Figure 8 is shows the arrangement of the optical components based on U.S. Patent 4,072,590 discloses the indicated prior art, the surface of the total reflection mirror M ₁ which constitute the laser oscillator as compared with FIG. 2 The shape is concave and there is no telescope. Note that the total transmission window W in the figure is shown for unification with FIG. 2, but is a plane that is flat on both sides and completely transmits the laser power, so that it does not exist as far as the spatial profile of the laser beam is concerned. Is equivalent to In the above arrangement, l ₁ = 2800 mm, l ₂ = 2800 mm R ₁ = 10000 mm (concave surface), R ₂ = R ₃ = R ₄ = ∞
FIG. 9 shows the results of ray tracing the spatial propagation profile of a Gaussian beam generated in the resonator when the total reflection mirror pair M ₁ and M ₂ are considered as a mirror for a laser resonator under the condition of (plane). Spatial profile of the laser beam between the contrasting this figure and FIG. 5 and the total reflection mirror M ₁ to the total transmission window W is greater by the total reflection mirror M ₁ near Naturally,
If there is a diffraction loss factor that restricts the laser beam diameter between M _{1 and} W, it becomes difficult to sufficiently extract energy from the laser medium. Further, a large laser power density cannot be expected in the vicinity of the reaction vessel 2.

[0014] In the reaction vessel 2, in order to achieve a relatively large power density, the total reflection mirror M ₂ As an example of the concave mirror, the optical component arrangement of Figure _{8, l 1 = 2800mm, l} 2 = 1200mm R FIG. 10 shows the results of ray tracing similar to FIG. 9 under the conditions of ₁ = 4200 mm (concave surface), R ₂ = R ₃ = ∞ (planar surface), and R ₄ = 6000 mm (concave surface). In this case, the reaction vessel 2 near, or beam profile among all transmission window W and the total reflection mirror M ₂ becomes smaller than that of FIG. 9, it is possible to increase the laser power density. However, as in FIG.
Spatial profile of the laser beam between the total reflection mirror M ₁ to the total transmission window W is greater by the total reflection mirror M ₁ near
On the other hand, in the vicinity of the all-transmission window W, the size becomes smaller as compared with that of FIG. In the above example, only the calculation results for the two types of condition settings are shown. However, realizing a laser power density higher than that on a reflecting mirror in a reaction vessel without impairing the laser energy extraction efficiency is conventionally known. It is clear that the law is difficult.

FIG. 11 shows another example of the arrangement of optical components according to the present invention. In this example, to reduce the number of optical components as compared to the arrangement of FIG. 2, Therese
A pair of condensing optical systems constituting the co-op includes a lens L ₂ ,
By a total reflection mirror M ₂ one constituting a laser resonator
It is configured. As the spatial mode behavior in this arrangement, as conditions equivalent to FIG. 6, l ₁ = 2800 mm, l ₂ = 500 mm, l ₃ = 1630 mm f ₁ = 800 mm R ₁ = R ₂ = R ₃ = ∞ (plane), R ₄ = 800 mm (concave surface) FIG.
Further, as conditions equivalent to FIG. 7, l ₁ = 2800 mm, l ₂ = 500 mm, l ₃ = 3210 mm f ₁ = 1600 mm R ₁ = R ₂ = R ₃ = ∞ (flat surface), and R ₄ = 1600 mm (concave surface) FIG. 13 shows the result of ray tracing calculation of a Gaussian beam. Referring to these figures, this configuration also provides
And similar to the results obtained in FIG. 7, the laser beam spatial profile between the total reflection mirror M ₁ to the total transmission window W while maintaining the same as that of FIG. 5, freely laser power in the reaction vessel 2 near It can be seen that the density, ie, the laser fluence, can be controlled.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a gas phase photochemical reaction apparatus using laser light according to the present invention will be described in detail based on embodiments. FIG. 1 shows an example of a gas phase photochemical reaction device according to the present invention. In the figure, a laser excitation unit 3 is an atmospheric pressure operated lateral excitation (TEA) CO ₂ laser tube. The laser total reflection mirror M1 is a planar grating arranged in a Littrow type in order to select _one of a large number of oscillation lines of a CO ₂ laser, and its angle is set to an oscillation wavelength of 9.57 μm. It is set as follows. The total transmission window W is a ZnSe window having flat surfaces on both sides and coated with a non-reflection coating, and is a window that shields the laser medium from the atmosphere and allows the entire laser beam to pass therethrough. When the laser excitation unit 3 is used as a normal laser oscillator, as shown in FIG.
An output mirror composed of a partial transmission mirror is installed at a position where the total transmission window W is installed. Laser excitation director, ie the distance between the total reflection mirror M ₁ to the total transmission window W is 2.8 m. When operated as a laser oscillator, the capability of the laser excitation section 3 is such that the pulse half width is about 80 nsec. , Capable of outputting a laser pulse having a pulse energy of 8 J / pulse.
At a position 50 cm to the right of the total transmission window W, a focal length of 160
nonreflective coating of cm is installed ZnSe condenser lens L ₁ which has been subjected, a position of 3.21m from there, concave total reflection mirror M ₂ gold coating is subjected curvature radius 1.6m installation with copper Have been. The above conditions are the same as the calculation conditions in FIG. The reaction vessel 2 is a cylindrical glass vessel, and a NaCl substrate whose incident angle is set to a Brewster angle is installed at both ends as a window for introducing a laser beam. The reaction substance 4 is configured to be introduced from one end of the reaction vessel 2, receive laser irradiation, and then discharged from the other end.

Using the above-described system, carbon 13 isotope enrichment was performed using CHClF ₂ as a raw material gas. As a result, C ₂ carbon 13 is concentrated 50-fold of a natural concentration
F ₄ was obtained as product, per laser pulse 13C
An efficiency of 8 × 10 ⁻⁷ mol / pulse was obtained as the separation efficiency. For comparison, a similar enrichment experiment was performed with the system changed to the condition of FIG. 10 corresponding to the conventional method, and as a result, an efficiency of 5 × 10 ⁻⁸ mol / pulse was obtained as the 13C separation efficiency per laser pulse. Was. Therefore, according to the present invention, the photochemical reaction efficiency per unit laser pulse energy has been improved more than ten times as compared with the prior art.

In the above embodiment, the TEA laser, which is a representative of the pulse CO ₂ laser, has been described as an example.
The present invention relates to other pulse CO ₂ by Q switch technology or the like.
Needless to say, the present invention can be applied to other lasers such as a laser, a continuous wave laser, and a solid-state laser or a dye laser.

[0019]

As described above, according to the present invention, it is possible to effectively use the power of the laser beam, which occupies the highest price in the gas-phase photochemical reaction process using the laser beam, and it It is possible to improve the reaction efficiency and reduce various costs of laser, and has an advantage that a low-cost laser gas phase photochemical reaction process can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a gas phase photochemical reaction device using laser light of the present invention.

FIG. 2 is a schematic diagram showing an example of arrangement of optical components according to the present invention.

FIG. 3 is a schematic diagram showing another example of the arrangement of optical components of the present invention, in which a telescope lens is replaced by a total reflection concave mirror as compared with FIG.

FIG. 4 is a schematic diagram showing an example of arrangement of optical components when a laser excitation unit is used as an oscillator.

FIG. 5 is a diagram illustrating a result of analyzing a spatial mode of a Gaussian beam generated in the resonator by ray tracing in the configuration of FIG. 4;

FIG. 6 shows a result of ray tracing of a spatial propagation profile of a Gaussian beam generated in the resonator when the total reflection mirror pair M ₁ , M ₂ is considered as a mirror for a laser resonator in the optical component arrangement of FIG. FIG.

FIG. 7 is a diagram showing an analysis result similar to FIG. 6 when the condition of the optical component is changed in the same arrangement as in FIG. 6;

FIG. 8 is a schematic diagram showing an example of arrangement of optical components according to the related art.

9 shows an optical component arrangement in the conventional method of FIG.
FIG. 11 is a diagram illustrating a ray tracing result of a spatial propagation profile of a Gaussian beam generated in the resonator when the total reflection mirror pair M ₁ and M ₂ are considered as mirrors for a laser resonator.

FIG. 10 is a diagram showing an analysis result similar to FIG. 9 when the condition of the optical component is changed in the same arrangement as in FIG. 9;

11 is a schematic view showing an arrangement example of another optical component of the present invention, example in which the telescope lens L ₂ and the total reflection mirror M ₂ by the same total reflection mirror M ₂ as compared with FIG. 2 It is.

FIG. 12 shows a result of ray tracing of a spatial propagation profile of a Gaussian beam generated in a resonator when the total reflection mirror pair M ₁ and M ₂ are considered as mirrors for a laser resonator in the optical component arrangement of FIG. FIG.

FIG. 13 is a diagram showing an analysis result similar to that of FIG. 12 when the condition of the optical component is changed in the same arrangement as in FIG. 12;

[Explanation of symbols]

1: Laser beam 2: reactor 3: laser pumping unit 4: raw material gas M _1: total reflection mirror M _2: total reflection mirror W: total transmission window M _3: concave total reflection mirror M _4: concave front reflector L ₁ , L ₂ : lens

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tatsuhiko Sakai 5-10-1 Fuchinobe, Sagamihara City, Kanagawa Prefecture, Nippon Steel Corporation Electronics Research Laboratory (56) References JP-A-2-251227 (JP, A JP-A-2-214526 (JP, A)

Claims (3)

(57) [Claims] An apparatus for introducing a laser beam into a reaction region in a reaction vessel in which a gaseous source material is present, and performing a desired chemical reaction using light absorption characteristics of the source material. In a gas-phase photochemical reaction device using a laser beam, which is composed of a pair of reflecting mirrors and inserts a reaction vessel into a laser resonator, a telescope consisting of a pair of condensing optical systems is provided in the laser resonator, and the laser between them A gas-phase photochemical reaction apparatus using laser light, wherein a reaction vessel is installed at a focusing position and a laser beam intensity in the reaction vessel is controlled by changing a focal length of a telescope optical system. 2. A gas phase photochemical reaction apparatus using laser light according to claim 1, wherein the telescope inserted into the laser resonator comprises a pair of lenses or a condensing reflector. 3. A pair of focusing optical systems constituting a telescope , one of which constitutes a laser resonator.
2. The method according to claim 1 , wherein the total reflection mirror comprises one total reflection mirror.
A gas phase photochemical reaction device using the laser light described in the above.