Resolution of sidebands in a semiconductor laser frequency modulated by ultrasonic waves

Frequency modulatlon or a semiconductor laser via ultrasonic waves is achieved at a modulating frequency
\omega_{m} - 150
MHz for CW operation at 4.2°K. Individual sidebands are resolved whose variation with pressure agree well with theory, indicating that little distortion is present. A modulation index of 6 is achieved corresponding to a frequency deviation of 900 MHz and an acoustic pressure of 3 atmospheres. Under pulsed operation at 4.2°K and 77°K frequency modulation is observed as a blurring of the laser frequency.