Simultaneous Q-switching and mode-locking in an intracavity frequency doubled diode-pumped Nd:YVO 4 /KTP green laser with Cr 4þ :YAG P.K. Mukhopadhyay a, * , M.B. Alsous b , K. Ranganathan a , S.K. Sharma a , P.K. Gupta c , J. George a , T.P.S. Nathan a a Diode Pumped Solid State Laser Laboratory, Department Atomic Energy, Center for Advanced Technology, Indore MP 452013, India b Atomic Energy Commission of Syria, P.O. Box 6091, Damascus, Syria c Biomedical Applications Section, Center for Advanced Technology, Indore MP 452013, India Received 6 February 2003; received in revised form 23 May 2003; accepted 27 May 2003 Abstract We report intracavity second harmonic (at 532 nm) generation in a passively Q-switched mode-locked Nd:YVO 4 laser. The width of a typical Q-switched envelope of the mode-locked pulses for the green laser was around 65  5 ns and the repetition rate for the mode-locked pulses was 400 MHz. The intracavity frequency doubling significantly improves the depth of modulation of the mode-locked pulses. The peak power of a single mode-locked green pulse near the center of the Q-switched envelope was estimated to be more than 2 kW and the average green power was 6 times higher than the CW green power at an incident diode pump power of 6 W. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 42.55.RZ; 42.55.Xi; 42.60.By Keywords: Mode-locking; Passively Q-switched; Nd:YVO 4 ; Cr 4þ :YAG; Intracavity second harmonic 1. Introduction Intracavity doubled second harmonic (SH) la- sers at 532 nm (green lasers) are useful for several applications, such as, under-water communica- tion, medicine, active imaging, holography and wafer inspection systems. However, continuous wave (CW) intracavity doubled green laser gener- ally suffers from a large noise fluctuation in the output due to the coupling of different longitudinal modes through the sum frequency generation at the frequency doubling crystal [1]. Mode-locking improves the average SH power stability by elim- inating longitudinal mode-beating by bringing all longitudinal modes into phase with one another. Further it leads to higher intracavity conversion efficiency due to high peak power ultra short pul- ses at the fundamental wavelength. Intracavity Optics Communications 222 (2003) 399–404 www.elsevier.com/locate/optcom * Corresponding author. Fax: +91-0731-48-8760. E-mail address: pkm@cat.ernet.in (P.K. Mukhopadhyay). 0030-4018/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0030-4018(03)01608-0