Proceedings - Viện Vật lý

_________________________________________________________________________________Những tiến bộ trong Quang học, Quang tử, Quang phổ và Ứng dụng. 8/2006, Cần Thơ, Việt Namwhere is the wavelength of laser beam.Since, the laser beam is enveloped by asymptote, which has two initialparameters such as: the radius 0and the initial divergent angle . Propagating innonlinear resonator, those parameters change, depending on rising and falling intime of pulse power. Meanwhile, the general transfer matrix changes with time,too. With about appoximately considering, the propagating equation, discribing theredistribution of laser beam, is given by: tn0 M t (20)t where n is the times of forth and back propagating in resonator of the giant pulse.3. Application for glass neodym laserThe influence of nonlinear effects in passive modulating cell and in the aciverod is investigated for the case of Glass Neodym laser JK 2000. As shown inprevious work [2], the giant pulse in linear regime has a beam waist to be30 0.2cm,a divergent angle to be about 30.10 rad . The laser pulse is of peak69power P 0 20. W and the duration 10.10 s . The passive modulating cellmax10with thicknesscoefficientl p 1cm, embedded by dicloroethane, which has the nonlinear index82n p 5.10 cm / W (χ (3) =5.5.10 -9 esu) [2,5,6], and the linear index2n 1,56 . The active rod has the length l a 7cm, the radius s 0. 4cm, the heatp61capacity C v 2.47 J / K , and thermal coefficient dn dT 7.310K . The pumppulse of lamp, which irradiate active rod, has the peak power about thousands watt3(to P peak0,T / 2 6.10 W ), and the duration about T 200s. The placement ofoptical elements in resonator is chosen such as: d1 10cm, d2 30cmandd3 37cm . Since that the total length of resonator is 75 cm, so one trip of the pulsetakes 5.10 -9 s and consequently, one pulse has to propagate forth and back, at leastfour times in resonator before going out, i.e., the integer n in Eq.(20) is chosen to be4.Beam Waist [cm]Beam Waist [cm]Peak power10 3 WFig.2 Beam waist vs peak power of lampFig.3 Change of beam waist in pulsing time:from up to down: 14, 16, 18, 20 MW364