Diode-pumped passively mode-locked Yb:LSO/SESAM laser

Diode-end-pumped passively mode-locked Yb³⁺:Lu₂SiO₅ (Yb:LSO) lasers both in the picosecond and the femtosecond regimes were demonstrated in this paper. The mode-locked lasers were initiated by using of semiconductor saturable absorber mirrors (SESAM). In the absence of intra-prisms for pulse compression, the laser emitted 1.6 W of output power with pulses width of about 4.3 ps. A pair of SF10 prisms was inserted into the laser cavity, pulses as short as 699 fs was generated around a center wavelength of 1043.6 nm with an average output power of 800 mW and a peak power of 11.0 kW.     

Self-stabilized energy-scalable dissipative soliton fiber laser

We report on the self-stabilized dissipative-soliton laser with an energy scalability by using a semi-conductor saturable absorber mirror (SESAM) as the pulse stabilizer for the first time. By tailoring the fluence on the SESAM relying on the two-photon absorption effect so that its reflectivity has a negative slope with respect to the fluence, the intra-cavity pulse dynamics is self-stabilized to produce single pulses only, resulting in a 48-nJ pulse energy and an unprecedented pump-to-output power conversion efficiency of 63%. Therefore, it resolves a long standing problem of the formation of multiple pulses in high-energy mode-locked lasers and thus opens a way to build high repetition-rate oscillators with ≥ microjoules pulse energies without any external amplifiers.     

High-stability passively mode-locked laser based on dual SESAM

A novel passively continuous-wave mode-locked laser by using two semiconductor saturable absorber mirrors (SESAMs) was demonstrated. The obtained average output power was 2.4 W with a pulse width of 9.97 ps and a pulse repetition rate of 127 MHz. The dual-SESAM mode-locked laser operation was more stable than the cases with single SESAM. The experimental results show that the long-term stability of the dual-SESAM mode-locked picosecond lasers provides promising potential for industrial applications.     

Passively modelocked surface-emitting semiconductor lasers

This paper will review and discuss pico- and femtosecond pulse generation from passively modelocked vertical–external-cavity surface-emitting semiconductor lasers (VECSELs). We shall discuss the physical principles of ultrashort pulse generation in these lasers, considering in turn the role played by the semiconductor quantum well gain structure, and the saturable absorber. The paper will analyze the fundamental performance limits of these devices, and review the results that have been demonstrated to date. Different types of semiconductor saturable absorber mirror (SESAM) design, and their characteristic dynamics, are described in detail; exploring the ultimate goal of moving to a wafer integration approach, in which the SESAM is integrated into the VECSEL structure with tremendous gain in capability. In particular, the contrast between VECSELs and diode-pumped solid-state lasers and edge-emitting diode lasers will be discussed. Optically pumped VECSELs have led to an improvement by more than two orders of magnitude to date in the average output power achievable from a passively modelocked ultrafast semiconductor laser.     

A 12.1-W SESAM mode-locked Yb:YAG thin disk laser

Pumped by a 940 nm fiber-coupled diode laser, a passively mode-locked Yb:YAG thin disk oscillator was demonstrated with a semiconductor saturable absorber mirror(SESAM). 12.1 W mode-locked pulses were obtained with pulse duration of 698 fs at the repetition rate of 57.43 MHz. Measurement showed that the beam quality was close to the diffraction limit.     

Diode-pumped passively Q-switched mode-locked Nd:LuVO4 laser with a semiconductor saturable absorber mirror

We present a compact passively Q-switched mode-locked Nd:LuVO₄ laser run in a Z-type folded cavity with semiconductor saturable absorber mirror (SESAM). The repetition rates of the passively Q-switched pulse envelope ranges from 22.99 to 141.18 kHz as the pump power increased from 2.372 to 8.960 W. The repetition rates of mode-locked laser pulses in the Q-switched pulse envelope has 111 MHz determined by the cavity length and the mode-locked pulse duration is evaluated to be 257 ps. An average output power of 823.5 mW is achieved at the pump power of 8.96 W, corresponding to an optical conversion efficiency of 9.2%.     

Subpicosecond pulse generation from a 1.56 μm mode-locked VECSEL

Near-transform-limited subpicosecond pulses at 1.56 μm were generated from an optically pumped InP-based vertical-external-cavity surface-emitting laser (VECSEL) passively mode-locked at 2 GHz repetition rate with a fast InGaAsNSb/GaAs semiconductor saturable absorber mirror (SESAM). The SESAM microcavity resonance was adjusted via a selective etching of phase layers specifically designed to control the magnitude of both the modulation depth and the intracavity group delay dispersion of the SESAM. Using the same VECSEL chip, we observed that the mode-locked pulse duration could be reduced from several picoseconds to less than 1 ps with a detuned resonant SESAM.     

Semiconductor saturable absorber mirror structures with low saturation fluence

We present two novel semiconductor saturable absorber mirror (SESAM) designs which can exhibit more than ten times lower saturation fluence than classical SESAM devices. Design considerations and characterization data are presented. These devices are particularly suited for passively mode-locked lasers with ultra-high repetition rates.     

Quantum-dot-based saturable absorber for femtosecond mode-locked operation of a solid-state laser

A quantum-dot-based saturable absorber has been demonstrated to initiate the generation of femtosecond pulses from a passively mode-locked solid-state laser. Control and tuning of the pulse duration from 58 ps to 158 fs was achieved. The 158 fs transform-limited pulses at 1280 nm are the shortest pulses that were produced from the Cr:forsterite laser passively mode locked by an InAs/InGaAs quantum-dot semiconductor saturable absorber mirror.     

In situ characterization of semiconductor saturable absorber mirrors in an operating Yb:KGW mode-locked laser

We report in situ characterization of a semiconductor saturable absorber mirror (SESAM) in an operating Yb:KGW mode-locked laser. The technique may be described as a pump-probe experiment in which the intracavity beam acts as a pump beam while the output of the same laser is used as a test beam for the SESAM reflectivity. At zero delay, the probe pulse overlaps in time with the subsequent intracavity pulse. The method is an alternative to standard pump-probe measurements in situations where the intracavity parameters such as energy fluence onto the SESAM, pulse length, and center wavelength cannot be achieved simultaneously with available lasers.     

Passive Q-switching and mode-locking for the generation of nanosecond to femtosecond pulses

The passive and hybrid Q-switching and mode-locking of solid-state lasers, dye lasers, semiconductor lasers and gas lasers is reviewed. The dynamics of saturable absorbers and reverse saturable absorbers is illustrated. The nanosecond pulse generation by passive and hybrid Q-switching of low-gain active media is described. The picosecond and femtosecond pulse generation by passive and hybrid mode-locking in low-gain and high-gain active media is analysed. The performance data of passively and hybridly mode-locked cw femtosecond dye lasers are collected. The pulse shortening of ultra-fast pulses with saturable absorbers in intra-cavity and extra-cavity configurations is discussed.     

7.6-W diode-pumped femtosecond Yb:KGW laser

We have demonstrated a high power diode-pumped mode-locked femtosecond Yb:KGW laser with semiconductor saturable absorber mirror(SESAM). By using an output coupler with 10% transmittance, the laser delivered 160-fs pulses with average output power of 7.6 W at a repetition rate of 78 MHz, corresponding to pulse energy of 97 nJ and peak power of 606 kW.     

Contrastive study of two SESAMs for passive mode-locking in Nd:YVO4 laser with low pump power

Two semiconductor saturable absorber mirrors (SESAMs), of which one is coated with 50% reflection film on the top and the other is not, were contrastively studied in passively mode-locked solid-state lasers which were pumped by low output power laser diode (LD). Experiments have shown that reducing the modulation depth of SESAM by coating partial reflection film, whose reflectivity is higher than that between SESAM and air interface, is an effective method to get continuous wave (CW) mode-locking instead of Q-switched power LD, in which no water-cooling system was used, could obtain CW mode-locking by the 50% reflector coated SESAM with average output power of ～ 20 mW.     

Diode-pumped femtosecond Yb:CaNb2O6 laser

We report to our knowledge a diode-pumped passively mode-locked Yb:CaNb(2)O(6) (Yb:CN) laser for the first time. Both CW and passive mode-locking operation of the laser are experimentally investigated. A maximum CW output power of 1.4 W with a slope efficiency of 20% is obtained on a 7 mm long 1.5 at.% Yb:CN crystal, while stable passive mode-locking with a commercial semiconductor saturable absorption mirror (SESAM) was achieved on a 3 mm long 3 at.% Yb:CN crystal. The mode-locked pulses have pulse width of 251 fs and an average output power of 44 mW at 1038 nm.     

Experimentally verified pulse formation model for high-power femtosecond VECSELs

Optically pumped vertical-external-cavity surface-emitting lasers (OP-VECSELs), passively modelocked with a semiconductor saturable absorber mirror (SESAM), have generated the highest average output power from any sub-picosecond semiconductor laser. Many applications, including frequency comb synthesis and coherent supercontinuum generation, require pulses in the sub-300-fs regime. A quantitative understanding of the pulse formation mechanism is required in order to reach this regime while maintaining stable, high-average-power performance. We present a numerical model with which we have obtained excellent quantitative agreement with two recent experiments in the femtosecond regime, and we have been able to correctly predict both the observed pulse duration and the output power for the first time. Our numerical model not only confirms the soliton-like pulse formation in the femtosecond regime, but also allows us to develop several clear guidelines to scale the performance toward shorter pulses and higher average output power. In particular, we show that a key VECSEL design parameter is a high gain saturation fluence. By optimizing this parameter, 200-fs pulses with an average output power of more than 1 W should be possible.     

Diode-end-pumped passively mode-locked Nd:LuVO4 laser with a semiconductor saturable-absorber mirror

A diode pumped passively mode-locked Nd:LuVO₄ laser with a semiconductor saturable-absorber mirror (SESAM) is demonstrated. The mode-locked pulses have a pulse duration of about 8.8 ps and a repetition rate of 157 MHz. Under an absorbed pump power of 12 W a maximum output power of 3.71 W is obtained, which gives an optical conversion efficiency of 31%. Our results show that Nd:LuVO₄ is a promising gain medium for the high power mode-locked solid-state lasers.     

Single-passed passively mode-locked Nd:YVO<Subscript>4</Subscript> picosecond laser with SESAM

We report on the LD-pumped passively mode-locked solid-state laser with SESAM (semiconductor saturable absorber mirror), in which the output beam is single passed through a flat mirror. The CW mode-locking pulse at 1064 nm, with an output power of 5 W, a pulse repetition rate of 98 MHz, and a pulse width of 25.3 ps. The beam quality is M ² < 1.12 and the optical-optical efficiency is 35.7%.     

Adjustable picosecond pulse duration in a LD end pumped SESAM passively mode-locked Nd:YVO<Subscript>4</Subscript> laser

With adjustable pulse durations, a semiconductor saturable absorber mirror (SESAM) passively mode-locked picosecond Nd:YVO₄ laser was studied. The pulse duration was adjustable from 20 to 80 ps by using intracavity etalons of different thicknesses.     

Q-switched and mode-locked diode-pumped Nd:YVO4 laser with an intracavity composite semiconductor saturable absorber

We have demonstrated a passively Q-switched and mode-locked Nd:YVO₄ laser with an intracavity composite semiconductor saturable absorber (ICSSA). Stable Q-switched and mode-locked pulses with Q-switched envelope pulse duration of 180 ns and pulse repetition rate of 72 KHz have been obtained. The maximum average output power was 1.45 W at 8 W incident pump power. The repetition rate of the mode-locked pulses inside the Q-switched envelope was 154 MHz. Experimental results revealed that this ICSSA was suitable for Q-switched and mode-locked solid-state lasers.     

Comparative studies of semiconductor saturable absorber mirror mode-locking dynamics in pulsed diode-end-pumped picosecond Nd:GdVO4 and Nd:YAG lasers

Ultrashort pulses were generated in passively mode-locked Nd:YAG and Nd:GdVO4 lasers pumped by a pulsed laser diode with 10-Hz repetition rate. Stable mode-locked pulse trains were produced with the pulse width of 10 ps. The evolution of the mode-locked pulse was observed in the experiment and was discussed in detail. Comparing the pulse evolutions of Nd:YAG and Nd:GdVO4 lasers, we found that the buildup time of the steady-state mode-locking with semiconductor saturable absorber mirrors (SESAMs) was relevant to the upper-state lifetime and the emission cross-section of the gain medium.