The acousto-optic mode-locking experiment is carried out for TEA(transversely excited atmospheric ) carbon dioxide laser. The mode-locking is achieved by an internal loss modulation of cavity light field.
Acousto-optic modulator consists of diffraction cell and transducer. The diffraction cell is made of GaAs single crystal with dimension of 1.2cm x 2cm x 1.4cm. Cavity axis is perpendicular to (110)plane and the propagation direction of longitudinal acoustic wave is perpendicular to (111) plane of crystal. The X-cut quartz transducer( resonant frequency : 28.86 MHz ) is driven by a RF unit. The RF power is 100W with the about 70% diffraction efficiency. The diffraction cell is operated in Bragg condition and is placed near the output coupler mirror. The cavity length of the laser is 2.6m.
The mode-locking is accomplished at homogeneous broadenning condition and the number of oscillation modes are 15 - 34 in the frequency domain. The output pulse train ( maximum peak power : 0.75MW ) with 17ns time interval is obtained and the width of the pulse at the center is 2-3 ns at half intensity. The temporal width of the pulse corresponds to 0.86 - 1.9GHz of the full width at half maximum in the gain curve.
