Xenon Flash Lamp Pumped Self-Frequency Doubling NYAB Q-Switched Laser

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1992 Chinese Phys. Lett. 9 463

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CHINESE PHYS. L E l L Vo1.9, %o.9( 1992) 463

Xenon Flash Lamp Pumped Self-Frequency Doubling NYAB Q-Switched Laser

Z H A S G Xingyu, ZHAO Shengzhi, WANG Qingpu, LIU Hua Optics Department, Shandong University, Ji'nan 250100

LU Baosheng, PAN Hengfu Institute of Crystal Materials, Shandong University, Ji'nan 250100

(Received 29 January 1992)

By using xenon Aash lamp as pumping light source and BDN dye film as pas- sive Q-switch or RD*P crystal as active Q-switch, we have, for the first time, realized Q-switching run from 1.06pm to 0.53pm in the N d , Yl-=A13(B03)4 (NYAB) self-frequency doubling laser and obtained AlW/cm2 giant pulse out- put at 0.53pm wave length. Meanwhile, thegreen light output energy and pulse duration were measured under the conditions of different resonator lengths and pumpings. The experimental results are in agreement with the numerical solu- tions of the Q-switching coupling wave rate equations. Moreover, the ways of improving the green laser output peak power are proposed.

PACS: 42 .55 .R~~ 42,65.-X-, 42.60.F~

NdzY1-zA13(B03)4 (NYAB) crystal is an ideal multifunctional material for minia- ture self-frequency doubling lasers because of its high Nd3+ ion concentration, large non-linear coefficient also because of its stable physical and chemical properties.'t2 It is believed that both the diode pumped NYAB cw miniature lasers and xenon flash lamp pumped NYAB Q-switched miniature lasers will have wide range of applications. Now m W output from diode pumped NYAB cw laser has been obtained and such high output from xenon flash lamp pumped NYAB free-run laser has also been a c h e i ~ e d . ~ However, xenon flash lamp pumped NYAB &-switched laser has not been reported yet. This paper reports the performance of the Q-switched laser pumped by xenon flash lamp with self-frequency doubling NYAB crystal.

In the experiment, 43 x 12" NYAB rod (cut at I phase-matching angle) was pumped by 44 x 40" xenon flash lamp. The pumping light was focused by a single silver-coated elliptical cylinder reflector and the laser cavity had a plane-plane config- uration. The rear mirror has nearly total reflection at A=1.06pm and a t A=0.53pm, while the output mirror has nearly total reflection for the fundamental-frequency wave (FFW) and nearly total transmision for all the second harmonic waves (SHW). BDN dyc film or K D * P crystal used as Q-siritch was located near the rear mirror. The XJ- .J1 energy meter and TEK-466 storage oscilloscope were used to measure the output energy and the pulse cliiration of 0.53 pni laser beam, respectively.

Combining the couplirig Lvave equation4 with Q-switched laser rate eq~iat ions.~ and iisirig the plane wave approximation. assuming the perfect phase-matching and ne- glecting thcl c1ifferc)nce lw tnwn group velocity and phase velocity, rve have obtained

464 ZHANG Xingyu et a l . V0l.Y

the following coupling wave-rate equations which describe the generation of FFW and SHW in the case that the cavity length is longer than the laser medium length.

Here, 11, I2 are the intensities of FFW and SHW; n is the density of inversion popu- l a t h ; B = 16x2v~(27r/cn2)~/cnl (v1 is the frequancy of FFW; n1,nz are the refrac- tive indexes of FFW and SHW); Xef f is the effective non-linear coefficient; t , is the cavity round-trip time; U is the stimulated emission cross section; I is the laser rod length; aI,az are the absorbtion coefficients of the crystal for FFW and SHW respec- tively; Tl,T2 are the transmissions of the dye for FFW and SHW (for dye Q-switch, TI/To = [(at I1/IS) / (u t IIT1/Is)]R-l, a=1/0.24, To is the small-signal transmission of the dye film, Is is the saturation intersity of the dye film. For electric-optical Q-switch, TI = Tz = 1); 61,& are the other losses of FFW and SHW.

0' 1 0 20 30

L ( c x n )

0' . - lo 20 30

I. ( e m )

Fig. 1: Relations h e t w e n E and L,7b for dye Q-switch. dye Q-switch.

Fig. 2 : Relations between T and L,T' for

a. . . . To=O.3, 2unol=3.01: a. ' . Toz0.3, 2uno/=3.01; h . 0 0 0 7;1=9.4, 2CT1101=2 4 3 ; b. o o o T0=0.4, 2ano/=2.43; C . x x )C 7;,=0.5) 2gt,uI=1.99. C . x x x To=0.5, 2 ~ n o [ = l . 9 9 .

Using cornputcr. we obtaiiicd the nu~iier ical solutions of the almve equations and the analogue output ci,,iractcristics of NYAB Q-switched laser (shown in Figs. 1-1). 'I'he related parameters arc shown in Table 1 .1,2i6

'The variations of 0..53//11\ laser energy ( E ) and pulse duration ( 7 ) versus the laser cavity length L under diffcrcnt pumping conditions are shown in Figs. 1-4, respectively. The solid lines arc !lie rcsulis of the numerical solutions (Ethe, T ~ , , ~ ) and the dots are the experimental data pcliiits T ? ~ ~ , ) . For the (1j.e Q-switch, we obtained 0.53 p r n giant pulse output o f :3 11s ~JuIs<~ c!ilic-itioll a i i d 1.2h i i i ~ cncrgy (6.10 h ~ / c n 1 ~ peak powcr) i n

90.9 ZIIANG Xingyu et al. 465

no (DYE) no (EO)

U

xeff

[ 2 c q l + 2ln( f ) + 51]/2al n1 = n2 1.755 61 (DYE) 0.01 K E,, /a1 Z, 1.58MW/cm2 61 (EO) 0.41

2.01 x IO-'' cmz =1 0.25 cm-' 62 (DYE) 2.01 6.82 x cm$/erg* =2 1.80cm-' 62 (EO) 2.41

0' 1 0 20 30 L(cm)

10.0-

7.5-

! L 5.0- "

2.5 -

Fig. 3: l h e relations between E and L , Ei, for EO Q-switcli.

iL. . . . E,,=24.0 J , 2a7lo/=3.00; b. o o o Ei,=19.2 J , 2anol=2.40;

Fig. 4: The relations between E and L , Ei, for EO Q-switch.

a. . - . E,,=24.0 J , 2ano/=3.00; b. o o o E i 4 9 . 2 J , 2ano/=2.40;

C . x x x E;,,=14.4.J, 2~710(=1.80. C. x x x Ein=14.4J , 2~nol=1.80.

We can see from the above figures that the experimental results are in good agree- ment with the theoretical calculations. Iiowever, there are also discrepancies between Eexp and Ethe: T~~~ and T ~ ~ ~ . The rcasons may be as follows: First, it is assumed in the- oretical calculation experimentally that the crystal is cut for perfect phase-matching. while i t is very difficult to cut a crystal tha t way, which fact causes the decrease of X e E

and results i n EeXp < Ell,s. Second, owing t o the size of the crystal cross section, the initial density of inversion population 710 and the pulse set up time between the centre and edge of the crystal are different. This leads to longer laser energy distribution time and results i l l rexp > T , ~ ~ .

In order to iinprove the K.53 /[in giant pulse output peak poww further, aside from cutting the crystal exactly for perfect phase-matching, we propose that it is importailL to develop large size NYA4n crystals and to reduce a2 by improving the optical quality of the crystal as well as optirniziiig Nd3+S/Y3f ion concentration, as shown in Figs.5 and 6,

466 ZIIANG Xingyu et al. F-01.9

Fig. 5: The relations between & e , rtbe and cry2 when L=lOcm, Ein=24.OJ for EO Q- switch.

Fig. 6: The relations between Ethe , T , ~ ~

and 1 when L=IOcm, Einz24.OJ for EO Q-s w i tch .

References

[l] B. S. Lu e l al., J . Appl. Phys. 66 (1989) 6052. 121 H. F. Pan el al., J. Phys; Condens. Mater. 2 (1990) 4525. [3] Z . D. Luo e l al . , Chin. Phys. Lett. 6 (1989) 440. [4] Y. R. Shen, T h e Principles of Nonlinear Optics (John Wiley & Sons, Inc. 1984) Chap. 3 . [5] J . J . Pegan, IEEE J . Quantum Electron, 25 (1989)214. [ G ] R . P. X u et al . , A Course in Laser Devices and Technologies (Beijing Institute of Tech-

nology 19SG) p. 156, 179 ( i n Cliincw).