Acousto-optic switch

ECDL External Cavity Diode Laser OI Optical Isolator L Lens AOS Acousto-Optic Switch PZT Piezo-Electric actuator Me Cavity mirror APD Avalanche Photodiode PC Pressure Controller P Pump... 

Nd YAG ceramic laser can be g-switched by using either of the active methods, such as electro-optic and acousto-optic switching, or passive methods, depending on the saturable absorptions. 

Often an acousto-optic switch is used, for example, for argon lasers and cw dye lasers [648]. Its basic principle is explained in Fig. 6.6. A short ultrasonic pulse with acoustic frequency / and pulse duration T 1 //s is sent nit = to through a fused quartz plate inside the laser resonator. The acoustic wave produces a time-dependent spatially periodic modulation of the refractive index n(t,z), which acts as a Bragg grating with the grating constant A = Cs//, equal to the acoustic wavelength A where Cg is the sound velocity. When an optical wave Eocos((ot — k r) with the... 

The aligned mirrors that surround the active medium and permit repeated passes of laser light through the inversion, form the resonator cavity. Aside from the active medium one can also place a variety of electro-optic switches inside the cavity, including Pockels cells, acousto-optic switches. 

The other key application of acousto-optic switching is based on generating a standing (or stationary) wave in a... 

FIGURE 3.19 Increasing the power of the acoustic wave will eventually cause saturation, where total diffraction occurs and the modulator performs as an acousto-optic switch. Turning the sound on causes the optical beam to deflect, and turning the sound off allows the optical beam to pass unperturbed. 

Often an acousto-optic switch is used, e.g., for argon lasers and CW dye lasers [11.24]. Its basic principle is explained in Fig. 11.6. A short ultra-... 

Our experiments differs from the ideal scheme in another respect the switching are not truly at random, since the acousto-optical switches are driven by quasi-periodic generators. Nevertheless, the two generators on the two sides function in a completely uncorrelated way, especially considering their frequency drifts. 

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

In a Q-switched laser, the population inversion, usually produced in the same way as CW operation, builds up by making the cavity quality factor Q unfavorable for lasing. Then, when the pump energy stored in the laser medium is at the desired level, the Q is suddenly adjusted (electro- or acousto-optically) to release the pulse. This results in high peak powers. 

The apparatus used to perform vibrational relaxation experiments in supercritical fluids consists of a picosecond mid-infrared laser system and a variable-temperature, high-pressure optical cell (68,73). Because the vibrational absorption lines under study are quite narrow (<10 cm-1), a source of IR pulses is required that produces narrow bandwidths. To this end, an output-coupled, acousto-optically Q-switched and mode-locked Nd YAG laser is used to synchronously pump a Rhodamine 610 dye laser. The Nd YAG laser is also cavity-dumped, and the resulting 1.06 pm pulse is doubled to give an 600 u.l pulse at 532 nm with a pulse duration of "-75 ps. The output pulse from the amplified dye laser ("-35 uJ at 595 nm, 40 ps FWHM) and the cavity-dumped, frequency-doubled pulse at 532 nm... 

Q switching of the fibre lasers by lasers using an acousto-optic modulator/rotating chopper results in peak powers of several watts in pulses in the range of 50 ns to 1 ps. 

Technological advances, i. e. cw pumped acousto-optically Q-switched Nd YAG lasers with repetition rates of up to 5 kHz combined with multichannel detection systems have increased the ease of obtaining hyper Raman signals. By making use of this advanced technology, hyper Raman spectra of benzene and pyridine could be obtained by Ned-dersen et al. (1989). Spectra from benzene, deuterated benzene and carbon tetrachloride have been obtained with high signal-to-noise ratios by Acker et al. (1989). As example, we show in Fig. 6.1-17 the hyper-Raman spectra of benzene and deuterated benzene. 

Polychromatic Acousto-Optic Modulator for rapidly switching and choosing laser lines (model number 48062-2.5-.55, Neos Technologies, Melbourne, FL, USA). 

With a front face-pumped compact active-mirror laser (CAMIL) structure, an Yb YAGAY AG composite ceramic disk laser with pumping wavelength at 970 run has been reported [210]. The laser was operated in both CW and Q-switching modes. Under CW operation, laser output power of 1.05 W with 2 % transmission OC was achieved at the wavelength of 1031 nm. Q-switched laser output was obtained by using an acousto-optic Q-switch, with repetition rates of 1-30 kHz and pulse widths of 166-700 ns. 

Another common switch, based on the acousto-optic effect, is sketched in Fig. 18. A piezo-electric transducer... 

FIGURE 18 The basic operation of an acousto-optic device is to reduce the intensity of a transmitted beam by diffraction from a refractive index grating that is generated, via the photo-elastic effect, by the RF power supplied to the transducer. The device depicted is used for Q-switching and cavity dumping. If configured as a resonator for the acoustic wave, it serves as a mode-locker. 

Figure 3.12 Realization of Q-switched laser action, (a) electro-optic Pockel cell/linear polarizer combination inserted into a pulse-pumped laser resonator (b) acousto-optic (AO) modulator inserted into a CW-pumped laser cavity. HR high reflector OC output coupler...

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