Picosecond Laser Source with Single Knob Adjustable Pulse Width

We describe and demonstrate a system which can be used with many types of actively modelocked lasers to create a source of variable width picosecond pulses. This system is an active compression scheme which incorporates a resonant electro-optic quadratic phase modulator to impart the linear frequency chirp on an optical pulse. To demonstrate, we used the modulator to chirp the 85 ps pulses from a modelocked Nd:YAG laser and subsequently compressed them with a dispersive delay line to less than 6 ps. It is possible with this system to smoothly vary the pulse width from the initial width to the fully compressed width buy changing only the RF drive power going to the phase modulator. It has come to our attention that the ever increasing demands and requirements on lasers used in RF photoinjectors has exceeded much of the currently available technology. Ongoing research of beam dynamics in high gradient accelerators, including studies on ultra-high brightness beam transport and emittance evolution, compensation, and maintenance, have led to strict requirements on optical pulse characteristics. Amplitude stability, peak energy, timing jitter, and pulse length tailoring are just some of the parameters of interest. Presently, there are many sources of short optical pulses available commercially. Unfortunately, most of these sources do not provide low timing jitter or much flexibility in their output pulse width due to cost or technological limitations. In order to overcome the pulse width deficiency, many groups have relied on pulse compression. In general, compression is obtained by first creating a frequency sweep (linear chirp or quadratic phase modulation) across the optical pulse and then using a linear dispersive delay of the proper sign to compress the pulse (remove the chirp).