Frequent modulation of dye lasers

This thesis describes an investigation into the effect of phase modulation within the resonator of a continuous wave (CW) dye laser. When the frequency of the modulation is close to, but not equal to, the longitudinal mode spacing, the output of the laser becomes characteristic of a frequency modulated (FM) carrier frequency. The original free running modes are replaced by modes separated in frequency by the modulation frequency, with FM phases, and Bessel function amplitudes. Unlike a mode-locked laser, the output intensity of the FM laser is completely CW with no modulation of the intensity. Although much research has been done in the past on the behaviour of mode-locked dye lasers, this appears to be the first investigation into the behaviour of frequency modulated dye lasers. The characteristics of both standing wave and uni-directional ring FM lasers are presented. The results of using FM dye lasers to perform sum-frequency generation and Doppler-free two-photon absorption are also presented. Both these techniques can make use of the properties of the FM spectrum and under the right conditions, can, in effect, provide demodulation of the laser at twice the carrier frequency. These may prove useful as methods of analyzing the spectral purity of a wide-bandwidth FM laser.