Coherent light generators – Particular pumping means – Electrical
Reexamination Certificate
1998-03-18
2001-03-06
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular pumping means
Electrical
C372S055000, C372S082000, C372S081000
Reexamination Certificate
active
06198762
ABSTRACT:
TECHNICAL FIELD
The present invention relates to supersonic and subsonic lasers which have a gaseous active medium, a nozzle, an RF discharge region, a laser active region, an optical resonator and a diffuser in order to produce a small, lightweight and closed gas system which is lightweight and very efficient. The laser of the present invention uses radio frequency (RF) excitation to generate a non-equilibrium plasma in the area of the sonic/subsonic or supersonic/subsonic gas flow. The high frequency discharge excitation may occur within the critical area of the supersonic nozzle or downstream from the critical area and may be enhanced by RF, electrical or UV pre-ionization of the gaseous active medium in the pre-critical area of the supersonic nozzle.
BACKGROUND OF THE INVENTION
Known gas laser systems use electrical discharges between DC or AC electrodes within transfer or axial flows. However, utilization of DC or AC electrodes, within fast subsonic and especially supersonic flows, creates unstable and non-uniform plasma discharges. These non-uniform discharges produce aerodynamic instability of the gas flow. This instability, characterized by wave shocks and turbulence, is proportional to the static pressure of the flow and volume in the discharge region between DC or AC electrodes. These limitations prevent creation of a stable, uniform and continuous plasma. In addition, AC/DC discharges create aerodynamic resistance for gas flows which requires a higher power gas pump. The aerodynamic instability of the supersonic and subsonic flows generated in the known gas lasers produce regions of increased temperature, related to the wave shocks, as well as temperature pulsation's, related to the turbulence. These factors are responsible for reduction of the laser inversion population, efficiency of the laser and optical quality of the flow within the resonator region.
Gas medium excitations utilizing glow DC or AC discharges are also well known. These laser designs, however, have other fundamental problems. The ARC plasma regions or those areas exhibiting sparking instability create a high atomic temperature of the laser gas which is therefore free from laser inversion population required for generating lasing activity and causes a breakdown in optical quality. Additionally, such sparking instability can lead to chemical composition breakdown of the gas active medium. Relative to the RF glow discharges, DC or AC glow discharges have a reduced energy contribution to the same volume of stable non-equilibrium plasma. Typically RF density requirement for excitation has a range from 10 to 100 watt per cubic cm., depending on RF frequency and type of RF plasma (Alpha or Gamma). In the case of DC and AC glow discharges for identical gas conditions the range of maximum possible densities is only from 1 to 5 watt per cub. cm. above which the sparking-plasma instability has taken place.
There is also a principle difference between natures of RF and DC/AC plasma structures. DC or AC discharges are based on the direct current of electrons and ions between an anode and a cathode. RF or High Frequency Discharge excitation is based on the high frequency oscillation of electron's boundaries located on the RF electrodes and stimulation of a “Positive Column” of ions and negative electrons between RF electrodes with the help of high frequency ionization by collision mechanisms. This means that DC and AC discharges are much more capable of the disintegration of chemical stability of the laser gas medium based on the dissociation, for example, of CO
2
molecules to molecules of CO and atoms of O. That is why RF discharges are superior to DC/AC type of discharges in the following respects: chemical stability of the laser gas; energy contribution to the volume of plasma; optical quality of the active medium; and level of power of gas pump required for providing gas medium flow.
SUMMARY OF THE INVENTION
The present invention is for a supersonic or subsonic laser having a radio frequency (RF) discharge excitation and utilizing a gaseous flow of active medium. The laser consists of a gas supply line which provides the gaseous medium through a cooling section into a receiver area. The gas may be supplied into the laser at a predefined pressure, depending upon the specific type of gas utilized. The gas passes through the supply line, cooling section and receiver at slow subsonic speeds.
Downstream of the receiver area is located a supersonic nozzle which opens into an optical resonator region and which also contains a localized excitation area. Downstream of the optical resonator region is located a diffuser which causes the deceleration of the supersonic or subsonic gas medium flow across the entire transverse cross-section of the supersonic nozzle. The laser of the present invention has a classic two-dimensional nozzle interior.
The laser device of the present invention provides for a high output power of laser generation and highly efficient use of the gaseous active medium in order to generate an extremely efficient laser while utilizing a simplistic design and relatively low energy supply. The laser can use various gases or mixtures of gases in combination with radio frequency discharge excitation between large square and flat RF electrodes in the area of sonic/subsonic or supersonic/subsonic flow of the gas active medium. The laser of the present invention utilizes a radio frequency (RF) discharge which creates a non-equilibrium “Alpha” or “Gamma” plasma through ionization and electron excitation of high states of atoms, molecules or ions in order to achieve a high inversion population necessary to generate lasing activity in the optical resonator region. The laser can utilize an open or closed loop system, said closed loop system enhanced by the ability of the laser to maintain the circulated gas at a low static temperature.
The laser of the present invention has a high frequency discharge region between wide linear RF electrodes in the area of the sonic/subsonic (M=1/M<1) or supersonic/subsonic (M>1/M<1) flow of the gaseous active medium. Radio frequency (RF) discharge creates a near uniform distribution of ions and electrons between plane electrodes. The radio frequency discharge region is located between RF electrodes and can be located within the critical area of the supersonic nozzle or downstream of the critical area within the supersonic area of the nozzle. The excitation region of the laser may have a more extensive area relative to the discharge region, depending upon the active medium or the pressure of the gas and may occur within the critical and supersonic areas of the nozzle up to the beginning of the optical resonator area. Alternatively, the location of RF electrodes and discharge region can be coextensive with the optical resonator region.
Within the optical resonator region is located the laser active region. This region is traversed by the resonator beam phases thereby taking advantage of the maximum level of laser inverse (inversion population) present and generating resonance photon amplification. The lasers generated by Radio Frequency excitation of the present invention are within the wavelength range from 2.03 mkm to 10.6 mkm.
Additionally, pre-ionization of the gaseous medium may take place in the pre-nozzle receiver area or within the critical area of the nozzle in order to aid in the creation of high frequency plasma required for ionization and electron excitation of the gaseous active medium in the excitation region. Such pre-ionization may be generated by a pre-ionization RF grid through which the gaseous medium passes. Alternatively, pre-ionization may be generated using ultraviolet bulbs or other UV sources as RF or AC plasma. The pre-ionization of the gaseous medium may be further enhanced by adding some portion of light ionization gas or vapor to the gaseous active medium.
Located downstream and at the end of the receiver area is a supersonic nozzle. The two-dimensional supersonic nozzle has an optimal logarithmic profile to insure a quiet
Arroyo Teresa M.
Inzirillo Gioacchino
Krasnov Yuri
Middleton & Reutlinger
Salazar John F.
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