Antonio Agnesi

Enhancement of stability and efficiency of a nonlinear mirror mode-locked Nd:YVO(4) oscillator by an active Q-switch.

The stability and the peak power of a nonlinear-mirror mode-locked Nd:YVO(4) laser are significantly increased by the insertion of an acousto-optic modulator inside the laser cavity. The repetition rate for reliable operation can be varied in the range 35 kHz - 50 kHz. The laser generates the most intense and stable mode-locked pulses of width 9 ps lying underneath a Q-switched envelope of width 110 ns with a Q-switch modulation frequency of 38 kHz. For 10 W of pump power, a 224 times enhancement of peak power over that of cw mode-locking is obtained under reliable Q-switched and mode-locked operation.

Diode-pumped neodymium lasers repetitively Q-switched by Cr/sup 4+/:YAG solid-state saturable absorbers

We report on the experimental results of a continuously diode-laser pumped Nd:YAG laser, operating at 1064 nm and repetitively Q-switched by a Cr/sup 4+/:YAG solid-state saturable absorber. End-pumping the Nd:YAG with a 10-W fiber-coupled diode-laser we could either optimize the energy or the average output power, depending on the choice of the saturable absorber and the output coupler. The maximum energy was /spl ap/200 /spl mu/J in single TEM/sub 00/, 17 ns pulses at 6 kHz, whereas a maximum average power of /spl ap/2 W with 32-ns pulses at 20 kHz was obtained. We also present preliminary results of a repetitively Q-switched Nd:YVO/sub 4/ laser at 1064 nm. The repetitive Q-switching operation is described by an improved model, which accounts for the behavior of both the active medium and the solid-state saturable absorber. The results of the model agree fairly well with the experimental data. Experimental results of second harmonic conversion are also reported and interpreted using a depleted pump model.

Efficient 671-nm pump source by intracavity doubling of a diode-pumped Nd:YVO 4 laser

A diode-pumped, intracavity-doubled Nd:YVO4 laser, generating as much as 760 mW of power at 671 nm, which was used to efficiently pump a Cr:LiSAF laser, is described. A slope efficiency of ≈39% with maximum continuous-wave output power of >180 mW was achieved with this system. Experiments in tunability and generation of ultrashort pulses are also reported.

40-fs Yb 3+ :CaGdAlO 4 laser pumped by a single-mode 350-mW laser diode

We report the results of the investigation on a passively mode-locked Yb(3+):CaGdAlO(4) laser, pumped by a single transverse mode laser diode emitting 350 mW at 980 nm. This particular pump source allows efficient pumping with a nearly TEM(00) beam and minimal thermal load, making the optimization of the mode-locking performance more straightforward than with higher-power multimode beams. Indeed, using a semiconductor saturable absorber mirror and extra-cavity dispersion compensation, pulses as short as 40 fs (31-nm spectrum) have been measured, tunable across 20 nm with 15-mW output power. Slightly longer Fourier-limited 46-fs pulses with 33 mW output power directly from the oscillator have been achieved, using a different saturable absorber mirror. Such overall performance, especially considering these are among the shortest pulses generated in diode-pumped ytterbium lasers, confirms the excellent qualities of Yb(3+):CaGdAlO(4).

High-brightness 2.4-W continuous-wave Nd:GdVO4 laser at 670 nm.

We report on a diode-pumped 1.3-microm Nd:GdVO4 cw laser, intracavity doubled for highly efficient generation of red light. We obtained as much as 2.4 W of power at 670 nm (corresponding to 26% optical-to-optical efficiency) in a nearly TEM00 mode and with small amplitude noise. To the best of our knowledge, these results represent the highest performance at this wavelength for cw solid-state lasers.

Single-walled carbon nanotube saturable absorber assisted high-power mode-locking of a Ti:sapphire laser

We report on passive mode-locking of a Ti:sapphire laser employing a single-walled carbon nanotube saturable absorber (SWCNT-SA) specially designed and fabricated for wavelengths near 800 nm. Mode-locked pulses as short as 62 fs were generated at a repetition rate of 99.4 MHz. We achieved output powers from the SWCNT-SA mode-locked laser as high as 600 mW with a slope efficiency of 26%. The characteristics of SWCNT-SA-assisted mode-locking were compared with those of Kerr-lens mode-locking without SWCNT-SA.

Sub-100-fs Cr:YAG laser mode-locked by monolayer graphene saturable absorber

We report on mode-locking of a Cr:YAG laser at 1516 nm using a monolayer graphene-based saturable absorber of transmission type generating 91 fs pulses with a Fourier product of 0.38 at an average output power exceeding 100 mW. Stable single-pulse mode-locked operation without any sign of Q-switching instabilities or multiple pulses is achieved.

28-W, 217 fs solid-state Yb:CAlGdO4 regenerative amplifiers.

A new high-performance Yb:CaAlGdO(4) (Yb:CALGO) regenerative amplifier is demonstrated. Pumped by 116 W at ≈980 nm and seeded by means of a 92 fs oscillator, it generates as much as 36 W of average output power with chirped pulses, and 28 W with 217 fs compressed pulses at 500 kHz repetition rate. This corresponds to 56 μJ of pulse energy and 258 MW peak power. The compressed pulses have a time-bandwidth product of 0.69 and could be shortened further with an improved compressor setup.

Graphene mode-locked femtosecond Yb:KLuW laser

Large-area monolayer graphene, synthesized by chemical vapor deposition, was transferred to a 1-in. quartz substrate. The high-quality monolayer graphene has been subject to characterization of the nonlinear properties near 1 μm and was successfully applied as saturable absorber for passive mode-locking of a femtosecond Yb:KLuW laser. The diode-pumped mode-locked Yb:KLuW laser was tunable around 1.04 μm and delivered pulses as short as 160 fs. The maximum output power of 160 mW was demonstrated for 203 fs pulse duration. The mode-locked laser results are comparable to those demonstrated with the same laser gain medium using single-walled carbon nanotubes as saturable absorbers.

Application of V3+:YAG crystals for Q-switching and mode-locking of 1.3-μm diode-pumped neodymium lasers

High-power passive Q-switching and mode-locking operation regimes of diode end-pumped Nd:YAG, Nd:YVO4, and Nd:YAP active media, operating at a 1.34-?m wavelength are investigated with V3+:YAG crystal as the saturable absorber. The highest average power of 2.1 W results from a Nd:YVO4 crystal placed in a 70-mm-long linear cavity. The corresponding pulse peak power and width are 0.1 kW and 133 ns, respectively. Employing a Nd:YAP crystal and 35-mm cavity length, the highest peak power of ~2.8 kW results when the laser runs at a 6.5-kHz repetition rate for an average power of —0.4 W. A record of 79-xJ pulse energy results from a 64-mm-long resonator with Nd:YAG gain media, however, for a decreased average power of ~0.24 W and pulses of 40-ns width. The mode-locking operation regime is investigated in a Z-type cavity. The best results, namely, ~0.5 W average power with mode-locked envelope energy in excess of 30 ?J and mode- locked pulse energy of 0.7 ?J, are obtained from the Nd:YVO4 media. Trains of 1-?s-wide pulses with improved stability result from a 1.5-m- long designed cavity with KTP crystal applied for passive negative feedback. A numerical modeling that takes into account the short recovery time of V3+:YAG saturable absorber (~5 ns) and excited state absorption effect is used to analyze and obtain general rules for optimizing such lasers.