Source: http://aoot.osa.org/oe/abstract.cfm?uri=oe-25-26-32457
Timestamp: 2019-04-20 07:11:40+00:00

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The advantages of simultaneous side and end diode pumping of Nd:YAG laser to enhance the spatio-temporal characteristics in the Q-switched mode of operation has been demonstrated. It has been shown that using a hybrid pump geometry in a short linear resonator provides a superior combination of output beam optical quality, energy, and pulse duration in contrast to the solitary use of an end-pump or a side-pump scheme at similar levels of average output power. We have demonstrated a compact single active rod Nd:YAG laser design in Q-switching mode with a pulse duration of 18 ns, pulse energy up to 3mJ, a repetition rate of 8 kHz, and М2 <2.
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Fig. 1 Stability diagram of the plane-spherical resonator with two thermally induced lenses with variable optical powers De, and Ds. The output coupler’s curvature radius is R2 = −500 mm (а), R2 = ∞ (b), R2 = 500 mm (c), resonator length is Lb = 135 mm. Zone I represents the stable region, zones II show the unstable regions for the resonator.
Fig. 2 [EP] – end-pump source; M1 – dichroic rear mirror (HR@1064 nm, HT@808 nm); [SP] – side-pump diode module with Nd:YAG active rod; TFP – thin film polarizer; M2 – output coupler (Roc = 78%); W1, W2 – optical wedges; FF – optical filters ; SM – spherical mirror; PWM – power meter, PD – high-speed pin-photodiode with oscilloscope.
Fig. 3 а) Side pump scheme, transversal distribution of fluorescence in the active rod and power parameters of [SP] and [EP] systems (ISP, IEP are the side- and end pump systems working current values respectively; b) output beam intensity distributions for the side-pump (1) and hybrid pump (2) operation modes; c, d) pulse energy and duration vs end-pump peak power PEP for different levels of side pump peak power PSP.
Fig. 4 Scheme of the laser with continuous hybrid pump. THE and THS – thermally induced lenses caused by end- and side pump radiation.
Fig. 5 Calculated dependences for the resonator with an output coupler radius of curvature R2 = −500 mm: a) g1g2 stability diagram; b) Magnification coefficient M for the resonator in the unstable configuration region. The area without isolines corresponds to the stable generation regime (M = 1).
Fig. 6 Transverse intensity distribution and generated pulse temporal profile for generation at 8 kHz; a) end-pump (IEP = 5 A), average output power Wg = 2.4 W, τg = 22 ns; b) side-pump (ISP = 24 A), Wg = 19 W, τg = 50 ns; c) side + end-pump (IEP = 6 A, ISP = 24 A), Wg = 21 W, τg = 18 ns.
Fig. 7 Experiment using CW end and side pumping -Stage II. Results at Q-switched repetition rate f = 8 KHz, a) Output pulse energy vs end-pump power PEP (PEP = WEP in the case of CW pumping); b) pulse energy vs side-pump power PSP at PEP = 32 W corresponding to the max output energy in Fig. 7(a).

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