Wavelength-specific laser-activated switches for improved contrast ratio in generation of short THz pulses

A method for designing and manufacturing wavelength-specific laser-activated reflection switches for use at THz frequencies is described. A key figure of merit for such switches is the contrast ratio, the ratio of power reflected after activation to that reflected before activation. The new switches improve the pulse contrast ratio by utilizing interference to suppress reflections prior to laser activation. Measurements using the University of California, Santa Barbara Free Electron Laser indicate that contrast ratios can be improved from approximately 60 to as large as 4.5×104 using the new switches. The switches improve contrast ratio by an average factor of 400, with peak improvement by a factor as large as 740. Such switches can be used in the generation of short THz pulses from narrow bandwidth sources and may also find applications in the extraction of single pulses from longer pulse trains.