Experimental techniques for generation of arbitrarily shaped and phased nanosecond and picosecond pulse trains

Abstract

We have shown, in a series of recent papers, that generation of laser pulse sequences with completely controlled delays, pulse shapes, and relative phases permits selective vibrational inversion, enhances velocity resolution in gases, and differentiates between relaxation mechanisms in condensed phases. We present new results with two fundamentally different technologies developed in our laboratory to produce such pulse sequences. Nanosecond pulse shaping and phase shifting is accomplished by acoustooptic modulation of a continuous ring laser.1 We have now experimentally demonstrated pulse envelopes as complicated as Such a complicated shape cannot be generated by other methods in the literature but is needed to compensate for inhomogeneous effects in electronic transitions. We routinely generate phase shifted pulse sequences using these and simpler shapes. Picosecond pulse shaping is accomplished by transient injection locking, and currently generates 150-ps, 10-μJ pulses. We can also generate subnanosecond phase shifts.2 Our fastest pulse shaper and electrooptic modulator, in conjunction with this injection locked system, generate a digital approximation to any shape we wish with <100-ps resolution.2 These results are in agreement with our theoretical models of transient injection locking. Technological limitations of these approaches and comparison with other methods are discussed.