FR2622060A2 - Gas laser with separate electron excitation and generation, by destabilising servocontrol of the metastable levels - Google Patents

Abstract

Enhanced high-efficiency gas laser device. The invention is linked with each of Claims 1 and 4 of the main patent. It makes it possible to boost the effectiveness of the device according to the said claims. The gas medium 1 is composed of three gases T, G, D. G is the principal gas from which arises the gas of the active centres C. D plays the fundamental role, it serves to deexcite the metastable level of C with the energy from which it generates the electrons by ionisation. The gas T is an auxiliary gas serving to boost the excitation of C. The present invention is characterised in that the partial pressure PD of the gas D is greater than a minimum reference value. The device according to the invention makes it possible to enhance the applications in industry, science, artisanship and artistry.

Description

 The present invention relates to an improvement to the national registration patent 8702325 dated FEBRUARY 23, 1987. The content of said patent relates to a gas laser device with population inversion and generation of electrons by destruction of metastable levels, thanks to the introduction into the gaseous medium of an auxiliary gas fulfilling the de-excitation function of said metastable levels by ionization.

 It is attached to each of claims (1) and (4) of said main patent.

According to claim (1) of the main patent, the gaseous medium is composed of three gases (T, G, D) such as:
-G is the main gas such as the gas designated by C of the active centers t defining itself cam being the particles whose energy levels are responsible for the emission of laser radiation by transition) is produced therefrom, and this in three forms possible according to practical cases, either in the natural state ie G itself as such, or in the form of G in the ionized state, or finally in the form of a product of chemical reaction or dissociation.

 - T is a make-up gas which serves to reinforce the excitation of C by energy transfer by collision or by the intermediary of photons. It can be made up of a single element or a mixture of several elements, atoms or molecules.

 - D plays an essential central role in the device, it serves to de-excite the active centers being in the metastable state and to simultaneously supply the electrons by ionization by collision with C or by 1 through photons (in the case where the metastable is a false metastable by imprisonment of the resonance photons). To this end, it is made up either of a single element, or of a mixture of several elements, atoms or molecules, the energy of first ionization of which is either less than the energy of the metastable, or. is fairly close (in the latter case the metastable level of C is located in the interval between the ionization level and the metastable level of the element or elements concerned).

 According to claim (4) of the main patent, the partial pressure of T is zero.

 The extensive systematic research work made it possible to strengthen the structure of the device according to each of the said claims of the main patent in order to obtain maximum efficiency.

To this end, according to the fundamental characteristic of the present invention, the partial pressure PD of D, brought to the reference temperature of zero degrees celsius, is relatively sufficient greater than a minimum pressure measured in millimeters of mercury) Po defined by :
Po = (gj.ai.Aji.760.22400) / (gi.aj.swN)
- gj being the statistical weight of the level j whose emission transition to the metast level, able i is chosen as the laser transition in order to trigger the latter and, if desired and if the spectroscopic and excitation characteristics of the levels of C are favorable, to trigger the stimulated transitions in cascade passing by j.

 - ai being the excitation rate (per cubic centimeters and per second) of level i, resulting both from direct electronic excitation and by cascade.

 - Aji being the spontaneous emission speed (per second) from j to i.

 - gi being the statistical weight of the metastable level i.

 - aj being the resulting excitation rate of level j.

 - s being the cross section of destruction of the metastable of C in the collision with D (in square centimeters).

 - w being the relative speed (in centimeters per second) of D compared to C calculated according to the kinetic theory of gases.

 - N being the number of AVOGADRO.

 - the dots and the bar / symbolize the arithmetic multiplication and division, respectively.

 In the case where D is a mixture, Po will be equal to the sum corresponding to each of the elements of the mixture, each of the terms of the sum being affected by its respective percentage.

 The partial pressure of G brought to the same reference temperature is chosen in a relatively wide range of values and in suitable proportion with PD, according to the criteria of efficiency of excitation of C, of interdiffusion of the mixture (G, D) , and laser amplification gain imposed by the type of optical resonator used. In practice and in general, it is several times greater than the value of PD.

 In fairly frequent practical cases, the value adopted for PD could be much lower than Po, thanks to many favorable physical factors such as the diffusion of metastable particles towards the walls, the ionizing collision of metastable particles between them, and especially thanks to external conditions when operating in periodic pulsed mode.

 According to another possible characteristic of the present invention, the value of PD can be low.

The present invention will be better understood on reading the following description of an embodiment given by way of experimental test in relation to the corresponding appended drawings, in which:
FIG. 1 represents the diagram of a resonator-telescope of confocal configuration known as unstable, with as ratio of the diameters of the large concave mirror and of the small convex mirror M = 1.5.

There are:
(1) the gaseous medium.

 (2) the electrodes for transverse excitation.

(3) the large silver concave mirror
(4) the small silver convex mirror
(5) the outgoing laser radiation.

 FIG. 2 represents the diagram of the laser transitions between the singlet levels 24P and 24S on the one hand, and between 34P and 24S on the other hand; the arrows represent the laser transitions that the present invention proposes to operate continuously. e) symbolizes the destruction of the 2S level.

The wavelengths of the transitions are as follows
- 34P - 24S: 501.56799 nanometers.

 - 24P - 24S: 2058.09 nanometers.

 Level 2S is metastable. Level 1 S is the fundamental level.

 The gaseous medium is a mixture of helium (He) and xenon (Xe); He plays the role of C, Xe plays the role of D.

The partial pressures Po are estimated as follows
- 3P-2S: Po = 42 millimeters of mercury.

 - 2P-2S: Po = 2 millimeters of mercury.

The present invention proposes the following values for the partial pressures PG of G and PD
- PG = 200 millimeters of mercury.

- PD = 60 millimeters of mercury
The present invention proposes, for the value of the parameter X / p, where X is the mean electric field in volts per centimeter and p is the total pressure of the mixture (He, Xe), the following mean value
- X / p = 15 volts per centimeter per millimeter of mercury.

 The present invention makes it possible to improve the efficiency of the device according to claims (1) or or (4) of main patent n-8702325 dated 23 FEBRUARY 1987. It makes it possible to strengthen the scientific, industrial and artisanal applications of said device.

Claims (1)

 1) Gas laser device with population inversion by destruction of the lower metastable level, with generation of electrons by slaving of said metastable according to claims (1) oA (4) of patent n8702325 date 23 FEBRUARY 1987, characterized in that the pressure partial PD of D, brought back to the reference temperature of zero degrees celsius, is relatively sufficient higher than a minimum pressure (in mm-Hg) of reference Po defined by  Po = (gj.ai.Aji.760.22400) / (gi.aj.s.w.N)  - gj being the statistical weight of the level j whose emission transition to the metastable level i is chosen as a laser transition in order to trigger the latter and, if desired and if the spectroscopic and excitation characteristics of the levels of C y are favorable, to trigger the stimulated cascade transitions passing through the level j.  - Aji being the spontaneous emission speed (per second) from j to i.  - ai being the excitation rate (per cubic centimeters and per second) of level i, resulting both from direct electronic excitation and by cascade.  - gi being the statistical weight of the metastable level i.  - aj being the resulting excitation rate of level j.  - s being the cross section of destruction of the metastable of C in the collision with D (in square centimeters).  - w being the relative speed (in centimeters per second) of D compared to C, calculated according to the kinetic theory of gases.  - N being the number of AVOGADRO.  - the dots ()) and the bar (/) represent the arithmetic multiplication and division respectively.  and in that in the case where D is a mixture, Po is equal to the sum corresponding to each of the elements of said mixture, each of the terms of the sum being affected by its respective percentage. PD can be much weaker than Po.  and in that in the case where the physical conditions are favorable and also in the case of operation in periodic pulsed mode, the value of  and finally in that the partial pressure PG of G can be chosen within a fairly wide range of values.