Volume 39, number 5 OPTICS COMMUNICATIONS 1 November 1981 HIGH POWER SUBNANOSECOND PULSE GENERATION IN Nd YAG LASERS C.H. BRITO CRUZ *, E. PALANGE and F. De MARTINI Istituto di Fisica "G. Marconi'; UniversitY, Roma 00185, Italy Received 12 May 1981 We desc~e the application of the self-injection and cavity dumping techniques to a Nd YAG laser. Single or double, highly stabilized nanosecond pulses are obtained with large efficiency. Recently, Liu [1,2] and, independently, Ewart [3] presented a novel and useful technique for the produc- tion of nanosecond and subnanosecond high power laser pulses in a stable, reproducible and efficient way, the so called self-injection (or cavity-flipping) technique. So far this idea has been applied to dye lasers [I .3] and Nd-YAG lasers [2]. In this letter we present what we believe to be a substantial improvement to this techni- que. In our scheme a single Pockels cell inserted in the laser cavity is used not only to perform the Q-switching and cavity-flipping actions [1,2], but also to dump out of the cavity single or double laser pulses. Apart from a simplification of the optical configuration, in this way we are able to minimize the cavity losses, to increase the coupling efficiency and to achieve pulse selection. The laser cavity is represented schematically in fig. 1 and its operation will be described on the basis of the time diagrams of fig. 2. At time t = to the voltage V ap- plied to the Pockels cell (PC) is switched from Vxl 4 to 0 allowing the onset of the Q-switched oscillation (fig. 2a). After an adequate delay r = t 1 - t o a Vx/2 square pulse of duration Tg is applied to PC. If Tg has a con- venient value, say one cavity round trip time T e = 2(L 1 + L2)/c, a seed pulse of duration 2L2/c is gener- ated in the cavity. This is the effect on which the cavity- flipping process is based [1-3]. The duration of the seed pulse is determined by the size of I.2 as pointed out earlier [3]. In addition it can be controlled by the time Tg of the Vx/2 pulse. The minimum duration is * On leave from Instituto de Fisica, UNICAMP, 13100 Campi- nas, BrasiL i L1 _j_ L 2 I 141 ~ -~ -'-I r=3.0m 100% ,( , 100% r output I0 Fig. 1. Laser cavity elements for self injection. PC is a Pockels cell and P a polarizer. Is is a Fresnel reflection from Pe used to probe the pulse evolution inside the cavity and Io is the cavity- dumped output. limited by the risetime of the PC driving circuit, Td, and can be found to be approximately 0.27 Td. A com- plete analysis of the dynamics of our device will be reported in a more extended paper [4]. The seed pulse is regeneratively amplified by the active medium and, when it attains its maximum amplitude, it can be dumped out of the cavity at t = t 2 by applying a V a = Vx/4 step to PC. As the seed pulse can be made substantially short (< 1 ns) the output peak power can attain large values. In fig. 2b the time evolution of the seed pulse circu- lating in the cavity is shown schematically. Fig. 2c shows the dumped out pulse. It should be noted that if at t = t 2 the light pulse is travelling through the section L 2 of the cavity, i.e. between PC and mirror M2, a single pulse is emitted for V d = Vxl4, as in fig. 2c. On the other hand, ff at t = t 2 the seed pulse is in the section L 1, a couple of pulses apart by T e will be emitted upon application of V a = Vx/4. The relative intensity of 0 030-4018/81/0000-0000/$ 02.75 © 1981 North-Holland 331