Experimental investigation of the all-optical acousto-optic effect for device applications

This thesis presents an experimental investigation into the all-optical acousto-optic effect. The all-optical acousto-optic effect is a method of controlling an optical beam with a second pulsed laser. The pulsed laser generates ultrasound in a material medium by means of thermoelastic heating. The ultrasound in turn modifies the index of refraction of the medium as described by the acousto-optic effect. The time and spatially varying index of refraction creates a phase grating, which can effect a probe optical beam. Several device concepts are presented based on the all-optical acousto-optic effect. Experimental observation of the all-optical acousto-optic effect is presented in the first chapter. Subsequent chapters refine the technique by experimental analysis of the main features of the technique. The analysis begins by determining the spectral characteristics of the generated ultrasound as a function of wavelength and pulse profile. The spectral information characterizes the acousto-optic interaction. It is determined that all-optical acousto-optic effect is a type of Raman-Nath diffraction and the best results are obtained using short wavelength lasers, with a narrow pulse width. An overall diffraction efficiency of 30 percent is obtained in tellurium dioxide. Several experiments are presented that analyze the all-optical acousto-optic interaction due to surface waves. The efficiency of surface acoustic wave generation using 266nm pulsed laser is demonstrated. Laser generated ultrasound experiments on black lithium niobate are performed, demonstrating an enhanced generation efficiency over conventional material. A method for providing numerical simulations is developed using a commercial package and post-processing the output. A means of calculating the general scattering potential for a medium due to the laser-acoustooptic interaction is presented. It is determined that the ultrasonic wave itself provides the most information about the all-optical acousto-optic effect. The simulations are compared to experimental results and used to demonstrate the behavior of a Mach-Zehnder lithium niobate device. This work provides the basis for future development of practical devices and characterizes laser requirements, material requirements, and substrate architectures.