Abstract

Our overall goal is development of Bragg cells with 200-µs delay and reasonable bandwidth. Mercurous bromide has an extremely low acoustic velocity, 273 m/s, which allows construction of a 200-µs cell with an acoustic path of only 5.5 cm. To exploit this slow acoustic velocity, the acoustic energy must be launched as slow shear wave propagating accurately along a n direction with the shear polarization in the n direction. From our measurements, a 3 dB attenuation is achieved in the 200-µs delay at an operating frequency of 36 MHz. Because mercurous bromide crystals are not readily available in the sizes needed, much of the program effort involved perfection of growth methods for optical-quality crystals of the required size. We were able to grow material that showed adequate optical quality and low scatter. Two Hg₂Br₂ Bragg cells were fabricated with lengths corresponding to approximately 180-µs delay. Lithium niobate transducers were mounted with a UV-cured polymer and were ground to thickness. Mercurous bromide has been shown to be a practical material for long-delay Bragg cells.

© 1990 Optical Society of America