This invention relates to short laser pulse generators of the type which pass the sidebands generated by a laser breakdown spark.
In the short history of the development of the laser art and its applications, which are only now beginning to unfold, laser-induced breakdown of gases has been an easily observed and dramatic effect. Recent experiments have shown that laser-induced breakdown of gases can be accompanied by substantial spectral broadening and self-phase modulation. Of more relevance for practical utilization is the observation that the breakdown plasma cuts off transmission of most of the incident beam in a time as short as 30 picoseconds.
The basic concept of short pulse generation from a laser spark is to employ a spectral filter that blocks the incident laser center wavelength but transmits a sideband produced by the sudden plasma growth. Among the types of spectral filters that have been suggested are the Michelson interferometer, the Fabry-Perot etalon and the grating monochromator. Of these only the grating monochromator can have sufficient rejection ratio to be of practical interest. Nevertheless, it is an expensive and inconvenient instrument to use and conventionally passes only one sideband yielded by the plasma.
It is desirable to obtain a more effective spectral filter, preferably a simpler one, for use in generation of short pulses by laser-induced breakdown in gases.