Specialty Yb fiber amplifier for microchip Nd laser: Towards 1-mJ/1-ns output at kHz-range repetition rate A.V. Kir’yanov a,b, * , S.M. Klimentov a , I.V. Mel’nikov a , A.V. Shestakov c a Optolink Ltd., bldg 5, Proezd 4806, Zelenograd, Moscow 124498, Russia b Centro de Investigaciones en Óptica, Loma del Bosque 115, Col. Lomas del Campestre, León 37150, Guanajuato, Mexico c E.L.S. Co., Ltd., ul. Vvedenskogo 3, Moscow 117342, Russia article info Article history: Received 24 June 2009 Received in revised form 28 August 2009 Accepted 31 August 2009 PACS: 42.60.Gd 42.55.Sa 42.55.Wd 42.55.Xi 42.60.By 42.60.Lh 76.30.Kg 42.81.Cn Keywords: MOFA Microchip laser Ytterbium fiber amplifier Specialty multi-port fiber Optimization abstract We demonstrate and optimize, for a mJ/ns release at the wavelength 1.064 lm, the operation of a com- pact laser system designed in the form of a hybrid, active–passive, Q-switched Nd 3+ :YAG/Cr 4+ :YAG micro- chip laser seeding an Yb-doped specialty multi-port fiber amplifier. As the result of the amplifier optimization, 1 mJ, 1 ns, almost single-mode pulses at a 1–10-kHz repetition rate are achieved, given by a gain factor of 19 dB for an 11-lJ input from the microchip laser. Meanwhile, a lower pulse energy, 120 lJ, but a much higher gain (25 dB) are eligible for the less powerful (0.35 lJ) input pulses. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The Q-switched microchip laser (ML) first suggested 20 years ago [1,2] is a flawless example of an alignment-free monolithic diode-pumped solid-state source that has several features which, especially the small footprint, make it highly desirable in a variety of both field-deployable and laboratory applications. The ML oper- ates normally in the near-IR with repetition rates as high as 500 kHz, intrinsically single-mode output spectrum, and high peak powers (tens of kWs), which are reached, however, at relatively low pulse energies not exceeding tens of lJs. Although the ML con- cept advantages open up a wide gate in applications associated with, e.g. a nonlinear wavelength conversion [3–5], the mentioned drawback, the low pulse energy, should be overcome to meet the demands of such technological applications as marking-type mate- rial processing, remote-target engagement, etc. The functionality of ML can be enhanced in this sense through the use of an external amplifier which design ought to satisfy the requirements of sim- plicity and compactness. Such an amplifier can take the form of an Yb fiber amplifier (Yb-FA) to boost up the lJ output of an Nd ML-based master oscillator (Nd-MO) towards the mJ level. Although the high gain that along with excellent thermal manage- ment capabilities is the main success of the Yb-FA architecture, this turns it into certain disadvantages at high powers: A set of optical nonlinearities that shows up at high powers can degrade temporal shape and spectrum of an output pulse, restrict the gain, and, sub- sequently, set an upper bound for the pulse energy and peak power. Since the offset of the nonlinearities (self-phase modula- tion, Raman- and Brillouin scatterings) is due to the tight light con- finement in the amplifying fiber core, it has been suggested to make use of such specialty fiber as Yb-doped photonic crystal fiber 0030-4018/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2009.08.062 * Corresponding author. Address: Centro de Investigaciones en Óptica, Loma del Bosque 115, Col. Lomas del Campestre, León 37150, Guanajuato, Mexico. E-mail address: kiryanov@cio.mx (A.V. Kir’yanov). Optics Communications 282 (2009) 4759–4764 Contents lists available at ScienceDirect Optics Communications journal homepage: www.elsevier.com/locate/optcom