RU2032259C1 - Excimer laser based on chlorides of noble gases - Google Patents

Abstract

FIELD: laser equipment. SUBSTANCE: excimer laser has HCl generator placed into gas stream after getter as source of gaseous hydrogen chloride. Getter is used for preliminary pumping out of laser chamber which enables it to be free from all other systems of exhaust and regeneration. Getter is made on base of alkaline metals (Ba, Ca, Mg, Li, K, Na) or on their mixture. Lack of large supplies of gaseous haloide in cylinders of gas bleeding-in system enhances safety of operation of attending personnel and diminishes risk of ecological pollution of atmosphere. EFFECT: enhanced operational safety and diminished risk of ecological pollution. 3 dwg

Description

 The invention relates to the field of quantum electronics, in particular, to excimer lasers with a closed system for regenerating a gas mixture.

 A known system for the regeneration of a gas mixture of an excimer laser on noble gas chlorides I using zeolite.

 A disadvantage of the known device is its low performance due to the rapid poisoning of the zeolite with halogen residues and the need for its frequent replacement, as well as the high cost of using the laser due to the high consumption of noble gases and the high cost of the systems themselves. In addition, the presence of a cylinder with a clean halogen creates the risk of poisoning the operating personnel in the event of a gas leak and requires additional measures.

 The closest in technical essence to the invention is an excimer laser based on noble gas fluorides and chlorides in the regeneration system of which successively high-temperature and cryogenic purification of the gas mixture is carried out [2]. For high-temperature cleaning, a getter based on titanium (for fluoride lasers) or on the basis of calcium (for chloride lasers) is used. In the getter, chemical interaction of the degradation products of the active medium with Ca or T takes place. Cryogenic purification allows adsorption of impurities remaining after passing through the getter gas mixture. To ensure complete cleaning, the process is repeated three times, passing the gas mixture through similar links. Everything, including basic halogen, halogen-containing compounds are filtered out, as they have increased chemical activity. Therefore, it is necessary to carry out an additional inlet of halogen into the working volume, and its quantity is strictly dosed. Halogen is often mixed with a noble gas (Ne or He), which leads to an increase in the pressure of the active medium, and starting from a certain pressure, additional pumping is required, as a result of which part of the noble gases are released into the atmosphere, i.e. the system is quasi-closed.

The disadvantage of this system is the high cost of laser operation due to the increased consumption of expensive noble gases. In addition, during the operation of cryogenic treatment, liquid nitrogen is consumed, which also increases the cost of operation. Another disadvantage of the system is the need to work with pure halogens (F ₂ , Cl ₂ , gaseous НСl) or their mixtures with noble gases (He or Ne), therefore there is always a danger of poisoning the operating personnel in the event of a gas leak, the total amount of which can be significant for providing the necessary laser time. Therefore, appropriate safety measures should be taken, for example, the use of expensive chemical resistant gas fittings, ventilation of adsorbents, which leads to an even higher cost of the system.

 The aim of the invention is to reduce the cost of operation of an excimer laser on noble gas chlorides by saving noble gases, increasing the safety of laser operation, as well as reducing the cost of an excimer laser by simplifying the design of the gas inlet system.

 This goal is achieved by the fact that as a source of gaseous hydrogen chloride, a controlled single-chamber or two-chamber HCl generator is used, which is turned on in the gas stream after the getter, and also that the use of a getter for preliminary pumping of the laser chamber allows you to completely abandon other pumping and regeneration systems.

The getter is made on the basis of alkali and alkaline earth metals (Ca, Ba, Mg, K, Na, Li) or their mixtures, which interact with most of the decay products of the excimer laser gas environment, as well as with all atmospheric components (except Ar) with N ₂ , O ₂ , CO ₂ and H ₂ O. This allows the use of getter as a fore-vacuum pump for preliminary pumping of the laser chamber of an excimer laser. The remaining one percent of argon weakly affects the kinetics of the excimer laser. Moreover, in the case of an ArCl laser, atmospheric argon can serve as the source gas for generating lasing. Operating temperature range of the getter lies in the range from 20 to 600 ^{° C,} depending on the metal used. For example, higher temperatures are needed when using Ca and Mg, which are practically inactive without heating.

A controlled generator of gaseous HCl is added to the regeneration system after the getter by the gas current, which is added to the gas mixture, which at the outlet from the getter consists mainly of a mixture of noble gases (Ne: Ar, He: Xe, Ne: Kr, etc.). Unlike a multi-stage regeneration system, unreacted impurities will re-interact with the getter during subsequent passes of the gas mixture through the getter. In the proposed design of the HCl generator, chemical reactions are selected in which gaseous HCl is formed inside the working volume as a result of a controlled chemical reaction initiated by heating one or more chemical components to a temperature of 30 to 600 ^about . The rate of HCl production depends on the temperature of the reagents. At the same time, in the inoperative state (at room temperature), the HCl release rate is practically equal to zero, and even during depressurization of the system there is no danger of poisoning the operating personnel. In addition, since large volumes of toxic gases have been eliminated, there is no need to use expensive chemical absorbers.

 The system allows for high-quality regeneration of the gas mixture, which is not accompanied by an increase in pressure in the laser chamber. Therefore, additional pumping of the chamber is not required, which can significantly increase the saving of expensive noble gases.

 Figure 1 presents a General view of the regeneration system; Figures 2 and 3 show design options for a gaseous HCl generator.

 The system operates as follows.

The gas mixture pumped out of the laser chamber 1 by means of a pumping system 2 enters the getter 3, where impurities are removed as a result of chemical reactions. The control device 4 of the Hcl 5 generator supports the currently required concentration of Hcl in the laser mixture. By varying the temperature of the heater 6 in the range from 30 to 600 ^{° C} can control the amount and rate of production of hydrogen chloride.

In the Hcl generator with a single chamber volume shown in FIG. 2, a mixture of two components is heated: solid chloride and alkali metal bisulfate. Heating initiates a chemical reaction, resulting in the formation of gaseous hydrogen chloride:
MCl + MHSO ₄ = M ₂ SO ₄ + HCl (1) where M is one of the alkali metals (K, Li, Na, Rb, Cs).

The temperature can be brought up to 600 ^° C, which greatly increases the rate of the chemical reaction and, consequently, the rate of HCl production.

In the Hcl generator with a two-chamber volume shown in Fig. 3, only one chemical component is heated - sulfuric acid, which fills the lower chamber 7. The heating temperature is 20 - 200 ^° C. The sulfuric acid vapors resulting from heating penetrate through the lattice 8 into the upper chamber 9, in which solid alkali metal chloride is located.

2MCl + H ₂ SO ₄ = M ₂ SO ₄ + 2HCl (2) (pairs)
Sulfuric acid vapor pressure varies with temperature and increases to 1 atm with increasing temperature up to 200 ^C. The design of the device can be supplemented by a thermoregulator.

 In the device, gaseous hydrogen chloride is formed inside the volume as a result of a chemical reaction initiated by heating non-aggressive substances. In both cases, there is no need to store pure Hcl, which increases the safety of working with an excimer laser. The use of chemicals in one case in the solid phase, and in the other case in the solid and liquid phases allows to increase the specific capacity for hydrogen chloride in terms of 1 liter of the volume of the gas system by at least 5 times.

As an example, consider a getter based on Mg:
2Mg + O ₂ __ → 2MgO (3)
Mg + 2H ₂ O __ → Mg (OH) ₂ + H ₂ (4)
MgO + H ₂ O __ → Mg (OH) ₂ (5)
That is, not only magnesium itself reacts, but also the products of the primary reactions.

3Mg + N ₂ __ → Mg ₃ N ₂ (6)
MgO + CO ₂ __ → MgCO ₃ (7)
Mg + H ₂ __ → MgH ₂ (8)
Mg + 2HCl __ → MgCl ₂ + H ₂ (9)
This is the basis of the reactions occurring in the getter, as a result of which solid, non-volatile substances are formed. Reactions (3) to (7) show the possibility of using a getter as a pump of atmospheric air. Reactions (8) and (9) along with reactions (3) - (7) are important for the regeneration of the gas mixture. Similar reactions occur with other alkali metals and with other impurities.

 A hydrogen chloride gas generator can be made based on any of the above reactions: (1) or (2).

 Of great importance on the characteristics of an excimer laser is the purity of the gas mixture, which fills the laser volume. This is due to the fact that the excimer laser radiation lies in the ultraviolet region: ArCl - 175 nm, KrCl - 223 nm, XeCl - 30 M nm. Any impurity absorbing in this region reduces the energy of laser radiation and degrades the characteristics of the excimer laser. The composition of the gas mixture includes expensive noble gases such as Xe, Kr, Ne, He. During operation, the gas mixture has to be replaced periodically due to its rapid degradation.

 The device of an excimer laser based on noble gas chlorides, including a getter based on alkali and alkaline earth metals and a generator of gaseous hydrogen chloride included in the gas stream after the getter, provides high saving of noble gases. In addition, the absence of large stocks of gaseous halogen in the cylinders of the gas inlet system increases the safety of staff and reduces the risk of environmental pollution.

Claims (1)

NON-GAS CHLORIDE EXXIMER LASER containing a laser chamber, a closed gas mixture regeneration system including a pumping device, getter, noble gas inlet system and a source of gaseous hydrogen chloride, characterized in that, in order to increase the economy and safety of the laser operation, as a source hydrogen chloride gas it contains a single-chamber or two-chamber controlled HCl generator, respectively, based on the reaction of interaction of alkali metal chloride and bisul alkali metal veil, heated to 600 ^o C, or by reaction of alkali metal chloride interact with vapors of sulfuric acid heated to 200 ^o C, mounted in the recovery system downstream of the gas mixture after the getter performed based on alkali metals Ba, Ca, Mg , Li, K, Na, or a mixture thereof, heated to 600 ^{° C.} and used to clean the gas mixture and pre-pump the laser chamber.

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