Gasdynamic CO.sub.2 laser and method for operating such a laser

In a gasdynamic CO.sub.2 laser mixing of hot and cold gasses takes place simultaneously with causing an inversion. The cold gas is air supplied through a compressor at a pressure in the range of 1 to 10 bar into the combustion chamber. Preferably the compressor output is supplied to two points of the combustion chamber, namely a zone directly upstream of and adjacent to the Laval nozzle and a zone in the combustion chamber further removed from the Laval nozzle.

BACKGROUND OF THE INVENTION 
The present invention relates to a gasdynamic CO.sub.2 laser and to a 
method for operating such a laser. In such a laser an inversion may take 
place simultaneously with the mixing of a cold gas with the hot combusting 
gas. 
German Patent Publication (DE-OS) No. 2,022,876 discloses gasdynamic 
CO.sub.2 -lasers in which the hot gas production is accomplished by the 
combustion of a fuel such as gasoline or benzene and so forth with the 
addition of oxygen. This type of laser, however, has the disadvantage that 
the pressure in the combustion chamber is very high. Such pressure may be 
within the range of about 30 to 100 bar. As a result, it is necessary to 
provide powerful compressors capable of providing a high volume oxygen 
supply. Such compressors must have a high compression ratio which in turn 
makes such compressors bulky. 
It has been suggested to increase the power of such gasdynamic laser 
systems by mixing a cold gas with the hot gas simultaneously with the 
occurrence of the normal inversion, produced by the adiabatic expansion in 
the laval nozzles. 
OBJECTS OF THE INVENTION 
It is the aim of the invention to achieve the following objects singly or 
in combination: 
to further improve a laser system operating under the hot and cold gas 
mixing priciple so that it will function by using the fuel gases still 
more efficiently; and 
to mix the cold gas with the hot gas at relatively low pressures as 
compared to the prior art. 
SUMMARY OF THE INVENTION 
The gasdynamic CO.sub.2 laser according to the invention comprises, in 
addition to its conventional components, a low pressure cold air 
compressor which is operatively connected to the combustion chamber by two 
channels for mixing cold air at a pressure within the range of 1 to 10 bar 
with the hot fuel gas in the combustion chamber and in the nozzle zone 
just upstream of the nozzle which causes an amplifier production of an 
inversion of the hot lasing gas.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
The present laser system comprises a combustion chamber 10 operatively 
connected to a resonator 12 by means of a Laval nozzle 11. The output of 
the resonator is conventionally connected to a diffuser 19. Fuel supply 
means including a fuel tank 14 and a fuel conveying pump 13 are 
operatively connected to the combustion chamber 10. The fuel tank 14 holds 
liquid fuel, such as gasoline or benzene and so forth. Atmospheric air 16 
is compressed in the compressor 15 to a pressure range within 1 to 10 bar. 
The output of the compressor 15 supplies the compressed air 17 into the 
combustion chamber 10 through a duct means 20 and 21. The duct 20 has a 
bent open end 22 feeding the compressed cold air into a nozzle zone 11' 
immediately adjacent to and upstream of the nozzle 11. The open end 22 of 
the duct 20 directly faces the nozzle 11 in axial alignment with the 
nozzle axis. By means of this arrangement it is accomplished that the 
mixing of the hot gas and the cold air takes place simultaneously with the 
production of an inversion during the expansion in the laval nozzle 11, 
whereby an enhanced inversion is achieved. The branch duct 21 supplies its 
air portion into the combustion chamber 10 at a point upstream of the zone 
11' as viewed in the flow direction from left to right in the 
illustration. The air supplied through the duct branch 21 functions as an 
oxidating means for combusting the fuel supplied through the pump 13 and 
for maintaining the combustion in the chamber 10. 
The cold air 16 is taken directly from the atmosphere and its pressure is 
increased by the compressor 15 to the relatively low range of 1 to 10 bar 
as compared to the compression required according to the prior art in the 
range of 30 to 100 bar. Further, the cold air is preferably moistened by 
introducing water droplets through a supply pipe 23 into the air flow. The 
water droplets may be introduced upstream or downstream of the compressor 
15. 
It is an advantage of the invention that the ratio of the flow 
cross-sectional area F of the flow channel upstream of the Laval nozzle or 
nozzles 11 to the flow cross-sectional area F* of the nozzle neck may be 
relatively small so that F/F* is about 3 to 1. Such relatively small ratio 
has become possible because the present mixing method provides a cooling 
of the hot gas 18 in the nozzle neck zone 11' to which the compressed cold 
gas 17 is supplied through the branch conduit 20 and the outlet 22. This 
in turn has the advantage that the cold gas requires only a small 
compression as disclosed above. Another advantage is seen in the fact that 
the cold gas directly cools the Laval nozzle or nozzles 11. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated, that it is intended, to cover 
all modifications and equivalents within the scope of the appended claims.