Pulse compression via cascaded quadratic nonlinearities

Summary form only given. Pulse compression is a well-established technique for generating optical pulses shorter than those produced directly by lasers or amplifiers. Most commonly, additional bandwidth is generated by self-phase modulation as the pulse propagates nonlinearly in an optical fiber. Compressors based on single-mode fibers are limited to nanojoule pulse energies by higher-order nonlinear effects and ultimately damage to the fiber. Thus, new approaches are needed for compression of the high-energy pulses that are now readily-available from regenerative amplifiers, for example. We describe a new approach to pulse compression based on quadratic nonlinearities. A negative (i.e. self-defocusing) nonlinear phase shift is produced in a phase-mismatched quadratic interaction. Normal dispersion is then required to compress the phase-modulated pulse, and this can be provided by a suitably-chosen piece of transparent material such as glass or sapphire. The use of a self-defocusing nonlinearity eliminates the problems that ordinarily arise from Kerr self-focusing during the propagation of intense pulses in bulk media.