We report on a passively mode-locked, diode-pumped femtosecond laser that provides ~200fs, 1053nm optical solitonlike pulses with < 8 orders of magnitude (OM) temporal contrast. The average output power of the compact, air-cooled laser is ~450mW at 77MHz pulse repetition rate. The spectral bandwidth (FWHM) is around 5-6nm, corresponding to transform limited pulses. For synchronization purposes the pulse repetition rate can be fine tuned to and continuously kept at a desired value employing a controller circuit, a motorized translation stage and a piezo actuator. The center wavelength of the pulses is tunable and can be precisely set to 1053nm by adjusting the laser pump power. The selfstarting laser is mode-locked using a semiconductor saturable absorber mirror (SESAM). The SESAM parameters are optimized for producing fs pulses with high temporal contrast. The effects of an intra-cavity fused silica plate inserted near Brewster angle and used for fine wavelength tuning and for polarization selection on the temporal contrast of the emitted pulses are discussed. The high temporal contrast pulses from this laser oscillator are well suited for seeding very high gain, multiple Joule type, Nd:glass, chirped pulse amplification systems routinely used in high intensity laser interaction experiments. The automated high dynamic range autocorrelator (HDR-AC) capable of recording the autocorrelation trace over 8 OM is described. The HDR-AC is based on a BBO crystal for second harmonic generation and a PMT for high sensitivity detection. A lock-in amplifier increases the detectable signal range by ~2 OM.
We present a passively Q-switched Nd3+:YAG/Cr4+:YAG laser with subsequent nonlinear pulse compression. This miniature laser combines both the high pulse energy of several tens of micro Joules and the short pulse duration of <20 ps without any amplification. It is therefore readily usable for many ultrafast applications including micro machining and medical applications. With these parameters, the laser shows a new level of compactness in comparison to other sub-100 picosecond laser sources. We utilize a Nd3+:YAG and a Cr4+:YAG crystal in a flat-Brewster, Brewsterflat configuration, respectively, positioned closely and the Brewster faces adjacent to each other. Pumped with approx. 6W from a fiber-coupled, 808 nm laser diode, the miniature, passively Q-switched laser oscillator delivers a pulse energy of 54 μJ with a pulse width of 339 ps and a repetition rate of 8.5 kHz. These pulses are subsequently coupled into a 20 μm core dia. large mode area PM fiber. Following a fiber propagation of 1.65 m the pulses are spectrally broadened by about a factor 40 due to self-phase modulation. Thereafter the nearly linearly chirped laser pulses are compressed by a chirped volume Bragg grating (CVBG). The optimized laser output pulses have a pulse width of 11.8 ps and a pulse energy of 20 μJ. We measured the polarized (PER<20dB) beam quality to be close to the diffraction limit with an M2≈1.5. A 13 hours continuous, stable laser operation has indicated a good long term stability and reliability.