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We report a continuous-wave high-output power and narrow-linewidth all-fiber laser at 1550 nm with the master oscillator power amplifier (MOPA) configuration. An all-fiber distributed feedback seed laser was boosted by three cascaded fiber amplifiers. In the experiment, we adopted a large-mode-area (LMA) Er3+:Yb3+-co-doped polarization-maintaining fiber to increase nonlinear thresholds and avoided the broadening of the laser linewidth. A linear-polarization fiber laser with average output power of 20 W, linewidth of 0.88 kHz, and power jitter less than 2% was finally achieved.

Spectral broadening due to amplified spontaneous emission (ASE) in a fiber amplifier is experimentally and theoretically investigated in this paper. By measuring and analyzing the variation in linewidth and noise of the fiber amplifier, the influence of ASE on laser linewidth is studied. The analysis shows that the ASE will cause broadening of the laser linewidth as noise, and the noise is introduced as an additive term rather than a multiplicative one.

Experimental investigation of single and dual pulses in a passively Q-switched Nd:YAG microchip laser with a Cr4+:YAG saturable absorber has been reported. The dual pulses consist of a main and a satellite pulse with respective spectra, intensities, and durations. It is found that the preponderant oscillating mode gives birth to the main pulse, and the other oscillating mode corresponds to the satellite pulse. Our results demonstrate that the dual-pulse emission results from double-longitudinal-mode oscillation in high pump regime.

A high energy dual-wavelength extracavity KTA optical parametric oscillator (OPO) with excellent stability and beam quality, which is pumped by a Q-switched single-longitudinal-mode Nd:YAG laser, has been demonstrated based on a type II noncritical phase matching (NCPM) KTA crystal. The maximum pulse energy of 10.2 mJ with the output stability of better than 4.1% rms at 3.467 μm is obtained at the repetition rate of 10 Hz and pulse width of 2 ns, and the 11.9 mJ of 1.535 μm radiation is obtained simultaneously. This extracavity NCPM KTA OPO is very useful when high energy, high beam quality and smooth time domain are needed., {"references":["S. T. Yang and S. P. Velsko, \"Frequency-agile kilohertz repetition-rate\noptical parametric oscillator based on periodically poled lithium\nniobate,\" Opt. Lett. 24, 133-135 (1999).","K. L. Vodopyanov and P. G. Schunemann, \"Broadly tunable noncritically\nphase-matched ZnGeP2 optical parametric oscillator with a 2-╬╝J pump\nthreshold,\" Opt. Lett. 28, 441-443 (2003) .","M. Henriksson, M. Tiihonen, V. Pasiskevicius and F. Laurell, \"Midinfrared\nZGP OPO pumped by near-degenerate narrowband type-I\nPPKTP parametric oscillator,\" Appl. Phys. B 88, 37-41 (2007).","X. J. Wang and Z. Y. Xu, \"Single-longitudinal-mode operation of a 1 W\ncombined actively and passively Q-switched Cr, Nd:YAG laser,\" Opt.\nExpress 13, 6693-6698 (2005).","R. F. Wu, K. S. Lai, H. F. Wong, W. J. Xie, Y. L. Lim, E. Lau, \"Multiwatt\nmid-IR output from a Nd:YALO laser pumped intracavity KTA OPO,\"\nOpt. Express 8, 694-698 (2001).","A. Dergachev, D. Armstrong, A. Smith, T. Drake, M. Dubois, \"3.4-╬╝m\nZGP RISTRA nanosecond optical parametric oscillator pumped by a\n2.05-╬╝m Ho:YLF MOPA system,\" Opt. Express 15, 14404-14413\n(2007).","P. Schlup, G. W. Baxter and I. T. McKinnie, \"Single-mode near midinfrared\nperiodically poled lithium niobate optical parametric oscillator,\"\nOpt. Commun. 176, 267-271 (2000).","M. Henriksson, M. Tiihonen, V. Pasiskevicius, F. Laurell, \"ZnGeP2\nparametric oscillator pumped by a linewidth-narrowed parametric 2 ╬╝m\nsource,\" Opt. Lett. 31, 1878-1880 (2006).","X. L. Dong, B. T. Zhang, J. L. He, H. T. Huang, K. J. Yang, J. L. Xu, C.\nH. Zuo, S. Zhao, G. Qiu, Z. K. Liu, \"High-power 1.5 and 3.4 ╬╝m\nintracavity KTA OPO driven by a diode-pumped Q-switched Nd:YAG\nlaser,\" Opt. Commun. 282,1668-1670 (2009).\n[10] D. L. Fenimore, K. L. Schepler, U. B. Ramabadran and S. R. McPherson,\n\"Infrared corrected Sellmeier coefficients for potassium titanyl\narsenate,\" J. Opt. Soc. Am. B 12, 794-796 (1995)."]}

Numerical simulation and analysis about the influence of the time modulation of the pump laser caused by mode beating on optical parametric process are presented with OPA and OPG as examples. It is shown that the output power of the generated beams from optical parametric process is modulated in the time domain and exhibits large power fluctuations, when a Q-switched laser oscillating on several random longitudinal modes is used as the pump laser. Irregular spike sequences of the generated beams are observed. We also find that the output power of the light from optical parametric process becomes more stable and exhibits a less fluctuation, when the number of the longitudinal modes (n) increases.