Nonlinear Interferometers for Laser Pulse Shaping

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Abstract
In a variety of laser applications there are requirements for devices which shorten laser pulses, emphasize the peaks, or act as a limiter to suppress peaks in the intensity. In this paper we consider several types of devices which can perform all these functions with subnanosecond response times. The emphasis in this paper is on the limiting function, however. All the devices are based on the concept of a dual-beam interferometer with a non-linear element in one or both beams. The nonlinear component can be either a saturable absorber or a medium exhibiting the optical Kerr effect. In the former case, the transmission of the absorber increases with increasing incident intensity; in the latter case, a phase shift is introduced as the intensity increases. By combining both beams at the output port of the interferometer with an appropriate static phase difference, these nonlinear effects can be made to produce either pulse peaking or limiting. In the same way, using two orthogonal polarizations and one beam, rather than two physically separated beams, one can construct a nonlinear polarization interferometer with the same characteristics but with reduced sensitivity to vibration and temperature changes. Theoretical and experimentally determined characteristics of several nonlinear interferometers are presented here. Of particular interest is a simple, inexpensive limiter with excellent shaping characteristics which we have demonstrated using a Nd:YAG laser at 1064 nm. This device operates for days without adjustment and can be designed for use with a wide range of laser wavelengths.

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