Method and apparatus for the production of pre-pulse-free, smooth laser radiation pulses of variable pulse duration

摘要

The pulse duration of an iodine laser is adjusted between 400 ps and 20 ns primarily by changing the resonator length in the range of about 2 cm to about 100 cm and secondarily by the ratio of excitation energy to threshold energy of the laser. Iodine laser pulses without pre- pulse and substructure are achieved in that the gas pressure of the laser gas of the iodine laser is adapted to the resonator length in order to limit the band width of the amplification and thus the band width of the pulse to be produced. The longer are the laser pulses to be produced the lower is the pressure chosen. A prerequisite for the above results is that the excitation of the iodine laser occurs extremely rapidly. This is advantageously achieved by photo-dissociation of a perfluoroalkyl iodide as CF.sub.3 I by means of laser providing sufficiently short output pumping pulses, e.g. an excimer laser, as a KrF laser or XeCl laser or a frequency-multiplied Nd-glass or Nd-YAG laser, or a N.sub.2 laser (in combination with t-C.sub.4 F.sub.9 I as laser medium). In addition to the substantial advantage of the easy variability of the pulse duration the method additionally has a number of further advantages, namely pre-pulse- free rise of the laser pulse up to the maximum amplitude; exchange of the laser medium between two pulses is not necessary at pulse repetition rates below about 1 hertz; high pulse repetition rates obtainable with laser gas regeneration; switching elements for isolating a laser oscillator from a subsequent amplifier cascade for the purpose of avoiding parasitic oscillations are not as critical as with flashlamp- pumped lasers.