Antiresonant Fabry-Perot Saturable Absorber Research Articles

Stable passively Q-switched operation of Tm3+ doped silica fiber laser by anti-resonant Fabry-Perot saturable absorber

We demonstrate a diode-pumped passively Q-switched Tm-doped double-cladding silica fiber laser operating at wavelength of 1960 nm using an anti-resonant Fabry-Perot saturable absorber as passive modulation element. To determine a relatively preferable fiber length for stable cw Q-switched operation, three active fiber simples with the length of 1.1, 5.3, and 7.0 m were employed respectively in our experiments. With 1.1 m gain fiber, we generated Q-switched pulses with a pulse width of 245 ns and an average power of up to 2.2 W at a repetition rate of 620 kHz. For the longer two fiber samples, Q-switched operation with longer pulse duration, Q-switched mode-locking and cw mode-locking were observed, respectively.

An antiresonant Fabry-Perot saturable absorber for passive mode-locking fabricated by metal-organic vapor phase epitaxy and ion implantation design, characterization, and mode-locking

We have fabricated GaAs-based antiresonant Fabry-Perot saturable absorbers (A-FPSAs) for passive mode-locking near infrared solid-state lasers using metal-organic vapor phase epitaxy (MOVPE) growth followed by ion implantation and optional thermal annealing. We present differential reflectivity measurements showing the effect of ion implantation and annealing. The devices were characterized for their large-signal response including saturation fluence, modulation depth, and nonbleachable losses-important parameters for passive mode-locking. Finally, we demonstrate mode-locking using our samples within a Ti:sapphire laser observing stable and reliable self-starting, pulses in the 100-fs range, and 50-nm tunability. Results of computer simulations are in good agreement with the experiments.

Self-starting soliton-modelocked femtosecond Cr(4+):YAG laser using an antiresonant Fabry-Pérot saturable absorber

We set up a self-starting passively modelocked femtosecond Cr.4C/:YAG laser using a low-finesse an- tiresonant Fabry-P ´ erot saturable absorber (A-FPSA). Stable transform-limited pulses were produced without the criti- cal cavity alignment necessary for Kerr lens modelocking. We achieved 114-fs pulses with 94 mW output power at the telecommunication wavelength 1:5 mm. The pulse formation is demonstrated to be due to soliton modelocking. At higher intracavity energy multiple pulsing was observed and is ex- plained by the saturation behaviour of the A-FPSA. In the multipulsing regime a pulse width as short as 95 fs and an averaged output power of up to 395 mW have been obtained.

GaAs based anti-resonant Fabry–Perot saturable absorber fabricated by metal organic vapor phase epitaxy and ion implantation

We have fabricated an antiresonant Fabry–Perot saturable absorber (A-FPSA), for potential use in laser passive mode locking, using metalorganic vapor phase epitaxy followed by ion implantation and thermal annealing. We show that the implantation/annealing cycle shortens the free-carrier dwell time without degrading the other optical properties of the A-FPSA.

56-ps passively Q-switched diode-pumped microchip laser

We passively Q switched a diode-pumped Nd:YVO4 microchip crystal with an antiresonant Fabry-Perot saturable absorber and achieved single-frequency pulses as short as 56 ps. We can vary the pulse width from 56 ps to 30 ns and the repetition rate from 27 kHz up to 7 MHz by changing the design parameters of the saturable absorber and the pump power.

60-fs pulses from a diode-pumped Nd:glass laser

We demonstrate 60-fs pulses with an average output power of 84 mW from a diode-pumped Nd:glass laser mode locked by a low-finesse antiresonant Fabry-Perot saturable absorber (A-FPSA). The mode-locked spectrum spreads over most of the available Nd:glass fluorescence bandwidth. At increased pulse energy fluence or decreased negative group-velocity dispersion, multiple pulsing was observed. We experimentally characterize this behavior, which can be explained by the saturation behavior of the A-FPSA and the limited available gain bandwidth. These considerations are significant for the design of saturable absorbers to achieve stable passive mode locking.

Efficient intracavity frequency doubling of a passively mode-locked diode-pumped neodymium lanthanum scandium borate laser

We passively mode locked a diode-pumped neodymium lanthanum scandium borate laser with an antiresonant Fabry-Perot saturable absorber and achieved 2.8-ps pulses at an average output power of 400 mW and a pump power of 1.2 W. With Ti:sapphire laser pumping we obtained pulses as short as 1.6 ps. Intracavity doubling produced 190 mW of 531-nm light for a diode-pump power of 1.2 W, resulting in a conversion efficiency of 48% with respect to the fundamental and 16% with respect to the diode-pump power. Noise characterization of the laser demonstrates a trade-off between high conversion efficiency and low intensity noise.

Passively Q-switched 180-ps Nd:LaSc_3(BO_3)_4 microchip laser

We passively Q switched a Nd:LaSc(3)(BO(3))(4) microchip laser with an antiresonant Fabry-Perot saturable absorber (A-FPSA) and achieved single-frequency, 180-ps pulses with 0.1 microJ of pulse energy at a repetition rate of 110 kHz. Because of the compactness and scaling possibilities offered by the A-FPSA, the pulse width can be varied from 180 ps to 30 ns and the repetition rate from 50 kHz to 7 MHz.

Femtosecond Yb:YAG laser using semiconductor saturable absorbers

We demonstrate a passively mode-locked femtosecond Yb:YAG laser using different semiconductor saturable absorber devices, a high-finesse and a low-finesse antiresonant Fabry–Perot saturable absorber. We achieved pulses as short as 540 fs with dispersion compensation and 1.7-ps pulses without dispersion compensation. We also mode locked the laser at either 1.03 or 1.05 μm by adjusting the band gap and antiresonance wavelength design of the antiresonant Fabry–Perot saturable absorber.

Scaling of the antiresonant Fabry–Perot saturable absorber design toward a thin saturable absorber

We demonstrate and discuss the scaling of the antiresonant Fabry-Perot saturable absorber toward a novel antiref lection-coated thin saturable absorber. With a Ti:sapphire laser we obtained self-starting Kerr-lens mode-locked pulses as short as 19 fs. With the higher modulation depth of the thin saturable absorber we obtained soliton mode-locked self-starting 34-fs pulses over the full cavity stability regime with a significantly shorter mode-locking buildup time. The pulse duration was limited only by the semiconductor Bragg mirror.

Control of solid state laser dynamics by semiconductor devices

We have successfully demonstrated that an appropriately designed semiconductor saturable absorber device, the antiresonant Fabry-Perot saturable absorber, can reliably start and sustain stable mode locking of solid state lasers such as Nd:YAG, Nd:YLF, Nd:Glass, Cr:LiSAF, and Ti:sapphire lasers. Especially for solid state lasers with long upper-state lifetimes, previous attempts to produce self-starting passive mode locking with saturable absorbers was always accompanied by self-<i>Q</i>-switching. We derive criteria that characterize the dynamic behavior of solid state lasers in the important regimes of <i>Q</i>-switching, mode-locked <i>Q</i>-switching, and continuous-wave mode locking in the picosecond and femtosecond range for the pulsewidth. We demonstrate that semiconductor absorbers can be designed to predetermine the dynamic behavior of a laser for a given solid state laser material and present an experimental verification. This allows for the development and design of robust, compact pico- and femtosecond solid state laser sources for scientific and industrial applications.

Diode-pumped mode-locked Nd:glass lasers with an antiresonant Fabry–Perot saturable absorber

We demonstrate passively mode-locked diode-pumped Nd:glass lasers with different media such as silicate, phosphate, and fluorophosphate that are homogeneously or inhomogeneously broadened. An antiresonant Fabry-Perot saturable absorber starts and stabilizes the soliton mode-locked Nd:glass lasers, producing pulses as short as 130 fs at an average output power of 100 mW. With a cw Ti:sapphire pump laser we obtain pulses as short as 90 fs.

Single-frequency Q-switched ring laser with an antiresonant Fabry–Perot saturable absorber

We passively Q switched a monolithic Nd:YAG ring laser [monolithic isolated single-mode end-pumped ring laser (MISER)] using an evanescent-wave coupled antiresonant Fabry–Perot saturable absorber. Single-frequency, 0.7-μJ pulses with a pulse width below 100 ns at an ≈1-MHz repetition rate are demonstrated. Pulse width and repetition rate can be varied by changing the distance and thus the coupling strength between the crystal and the absorber.

Diode-pumped 100-fs passively mode-locked Cr:LiSAF laser with an antiresonant Fabry–Perot saturable absorber

We demonstrate a self-starting passively mode-locked diode-pumped Cr:LiSAF laser, achieving pulses as short as 98 fs with an average power as high as 50 mW. In continuous-wave operation, we demonstrate 140 mW of output power with a tunability of 100 nm FWHM. These results were achieved by use of lower Cr(3+) doping (1.5%), high-brightness diode lasers pumping from both sides of the crystal, and a low-loss antiresonant Fabry-Perot saturable absorber to start and sustain mode-locked operation.

Ultrafast all-solid-state laser technology

Passively mode-locked diode-pumped solid-state lasers can provide practical high-power laser sources with pico- and femtosecond pulse durations. We use semiconductors not only to optically pump but also to cw mode-lock or Q-switch a solid-state laser. A novel saturable absorber design, the Antiresonant Fabry-Perot Saturable Absorber (A-FPSA), allows of using semiconductor saturable-absorber materials even though they are generally not well-matched to the characteristics required for diode-pumped solid-state lasers, i.e., the semiconductors tend to have too much optical loss, a too low saturation intensity, and a too low damage threshold. This paper gives an overview of passively mode-locked ion-doped crystalline solid-state lasers. In particular, we present a quantitative discussion of A-FPSA mode locking, and compare A-FPSA mode locking with other passive mode locking techniques such as KLM (Kerr Lens Mode locking).

Self-starting diode-pumped femtosecond Nd fiber laser

A self-starting passively mode-locked diode-pumped neodymium fiber laser with a semiconductor antiresonant Fabry-Perot saturable absorber (A-FPSA) is demonstrated for the first time to our knowledge. Mode locking can be initiated and maintained by the semiconductor absorber, and pulse durations down to 260 fs are routinely obtained. Alternatively, shorter pulses (60 fs) were generated by exploition of nonlinear polarization evolution in the fiber (in combination with a stronger pump source) where the A-FPSA simply initiates the pulse-forming process.

Self-starting femtosecond mode-locked Nd:glass laser that uses intracavity saturable absorbers

We produced transform-limited pulses as short as 130 fs with 160-mW average output power from a passively mode-locked Nd:glass laser. This is to our knowledge the first demonstration of an intracavity semiconductor antiresonant Fabry–Perot saturable absorber continuously starting a Kerr-induced passively mode-locked laser. The antiresonant Fabry–Perot saturable absorber, even with dispersion compensation, produced only picosecond pulses, and femtosecond performance was observed only with the addition of an intracavity long-pass wavelength filter. We propose a new mode-locking mechanism, which we refer to as Kerr-shift mode locking, in which the wavelength-dependent intracavity aperture and self-phase modulation in Nd:glass combine to produce a self-wavelength shift that reduces intracavity losses for femtosecond pulses.

Passively mode-locked diode-pumped solid-state lasers that use an antiresonant Fabry–Perot saturable absorber

We report passively mode-locked diode-pumped Nd:YAG and Nd:YLF lasers that use an antiresonant Fabry–Perot saturable absorber. For Nd:YLF at 1047 nm, we achieved pulses of 5.1 ps FWHM with 225 mW of average power. For Nd:YAG at 1064 nm, we achieved pulse widths of 8.7 ps with 100 mW of average power. Both lasers ran at a repetition rate of 100 MHz. The frequency stability of the free-running lasers was sufficient to allow locking of the laser repetition rate to a synthesizer by using a phase-lock-loop feedback system.

Self-starting and self-Q-switching dynamics of passively mode-locked Nd:YLF and Nd:YAG lasers

The semiconductor antiresonant Fabry–Perot saturable absorber (A-FPSA) has a bitemporal absorption response with a slow time component that is due to carrier recombination and a fast time component that is due to intraband thermalization. We demonstrate that the slow component provides the self-starting mechanism and without significant Kerr lens contribution the fast component is necessary for steady-state pulse formation in passively cw mode-locked solid-state lasers. The carrier lifetime of the bitemporal A-FPSA was varied by the molecular-beam-epitaxy growth temperature to characterize its influence on the self-starting and self-Q-switching dynamics of cw mode-locked Nd:YLF and Nd:YAG lasers. The A-FPSA carrier lifetime and the top reflector of the A-FPSA can be adjusted to optimize the self-starting performance and to prevent self-Q-switching of cw mode-locked solid-state lasers.

Solid-state low-loss intracavity saturable absorber for Nd:YLF lasers: an antiresonant semiconductor Fabry–Perot saturable absorber

We introduce a new low-loss fast intracavity semiconductor Fabry-Perot saturable absorber operated at anti-resonance both to start and sustain stable mode locking of a cw-pumped Nd:YLF laser. We achieved a 3.3-ps pulse duration at a 220-MHz repetition rate. The average output power was 700 mW with 2 W of cw pump power from a Ti:sapphire laser. At pump powers of less than 1.6 W the laser self-Q switches and produces 4-ps pulses within a 1.4-micros Q-switched pulse at an approximately 150-kHz repetition rate determined by the relaxation oscillation of the Nd:YLF laser. Both modes of operation are stable. In terms of coupled-cavity mode locking, the intra-cavity antiresonant Fabry-Perot saturable absorber corresponds to monolithic resonant passive mode locking.