A balanced CPM ring dye laser was fabricated. Pulses as short as 62 fs was measured using a second-harmonic generation autocorrelator. The optimum conditions were studied by changing the concentration of saturable absorber, pumping power of $Ar^+$ laser, and alignment of the dispersion-compensation, intracavity prisms.
For the characterization of the ultrashort pulses, a stepping motor-controlled autocorrelator and a real-time autocorrelator were constructed. Subpicosecond pulses from the CPM ring dye laser were measured with the stepping-motor-controlled autocorrelator and ps pulses from the hybridly mode-locked dye laser were measured with the real time autocorrelator. The real-time autocorrelator is quite important in order to maintain hybidly mode-locked dye laser which is very sensitive to cavity length, pumping power, concentrations of gain dye and saturable absorber. The cavity length detuning characteristics of the hybridly mode-locked dye laser has been studied. In the optimum condition, the pulse width of 0.65 ps was obtained. As the cavity length is increased, the pulse width becomes broader than the optimum width and spectrum bandwidth is also broadened. The peak power of autocorrelation is maximum at $\Delta$1 = 5.0 μm longer than optimum cavity length. On the other hand, as the cavity length is decreased, the pulse width becomes broader and satellite pulses appear because of the gain recovery. Also the spectrum band width becomes narrower than that of the optimum cavity length.
Employing one color pump-probe method the excited F-center was studied. The one color pump-probe measurement monitors transient absorbance change at the pump beam wavelength with relative delay time between pump and probe beams. Generally the rise time of transient absorption is same as the instrument response time. However, the rise time of transient absorption of F-center in RbCl is much longer than the instrument response time of the measurement system. The laser beam had a repetition rate of 400 kHz with 1.4-1.8 ps pulse width. But the deconvoluted rise times were 2.6, 2.0 and 0.6 ps from the transient absorption measurement in RbCl at 570, 590, 610 nm, respectively. The wavelength-dependent rise time of transient absorption in RbCl indicates tha it is the lattice vibrational relaxation time since the excited state can absorb photons as well as the ground state until it relaxes vibrationally.
The output power of the $CO_2$ laser is stabilized by the feed back control of the electrical discharge through an auxiliary electrode. The laser output is monitored by a HgCdTe detector, and to suppress the output fluctuations, the variable voltage is applied to the auxiliary electrode located near the ground cathode. With this stabilization technique, the output power fluctuation is reduced to about one-tenth of that without stabilization.