Semiconductor saturable absorber mirror structures with low saturation fluence (original) (raw)
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The reduced temporal parameters of passivated semiconductor saturable absorber mirror
Thin Solid Films, 2009
It is shown that plasma-enhanced chemical-vapor deposition of SiO 2 antireflective layer can result in significant reduction of the recovery time of semiconductor saturable absorber mirror (SESAM). The results were compared to the SESAM structure capped by SiN X layer and native oxide. The recovery time of the SESAM devices was characterized by pump-probe measurements. We have obtained recovery times of 25 ps, 11 ps and 2.6 ps for native oxide, SiN X and SiO 2 layers, respectively. These results can be explained by differences in the density of surface states which exist after passivation processes. Using SESAM with an SiO 2 antireflective cap layer, we have demonstrated a mode-locked diode-pumped Yb:KY(WO 4 ) 2 laser generating near band-width limited pulses. We have used the passivation process to reduce the pulse duration.
Journal of Applied Physics, 2009
We have developed a mode-locked diode-pumped Yb: KY͑WO 4 ͒ 2 laser generating nearly bandwidth limited pulses as short as 101 fs. At 1.1 W of absorbed power and for 3% transmission output coupler, the laser delivers 150 mW in pulses of 110 fs duration, which corresponds to the efficiency of 14%. This has been achieved using semiconductor saturable absorber mirror ͑SESAM͒ grown by molecular beam epitaxy. The low-temperature ͑LT͒ absorbers were crystallized under the carefully optimized growth conditions. The resonantlike type structures ensured relatively high enhancement factor and in consequence high absorption modulation. The main device parameters such as group delay dispersion ͑GDD͒ and enhancement factor were chosen to be wavelength independent. The optimization of the growth conditions resulted in a reduction in the nonsaturable absorption in as-grown LT-InGaAs absorbing layer and ensured the fast carrier trapping and recombination. We assume that the nonsaturable losses of the annealed LT layers result from the absorption connected with defects generated in the crystal during LT growth. Moreover, the annealing deteriorates the interface sharpness and the crystal quality of LT pseudomorphic, nonstoichiometric InGaAs layer. On the other hand, higher growth temperature and lower ratio of group V to group III beam equivalent pressure ͑V/III ratio͒ ensure lower defect densities and high crystal quality but suffer from the absorption related to As Ga 0 conduction band transitions. The careful balancing of these contradictory tendencies allowed for optimization of the absorber properties. The InGaAs quantum well absorbing layer was grown at the temperature as high as 420°C, under the V/III ratio as low as 10. No postgrowth annealing was performed. The recovery time of the SESAM structure characterized by the pump-probe measurements was equal to 9.6 ps. The nonsaturable losses of 1.94% decreased the modulation depth to 1.48% but still self-starting and stable mode locking was observed. The saturation fluence of 27 J / cm 2 did not suffer significantly from a little bit too high nonsaturable losses.
New regime of inverse saturable absorption for self-stabilizing passively mode-locked lasers
Applied Physics B, 2005
The reflectivity of a semiconductor saturable absorber mirror (SESAM) is generally expected to increase with increasing pulse energy. However, for higher pulse energies the reflectivity can decrease again; we call this a 'roll-over' of the nonlinear reflectivity curve caused by inverse saturable absorption. We show for several SESAMs that the measured roll-over is consistent with two-photon absorption only for short (femtosecond) pulses, while a stronger (yet unidentified) kind of nonlinear absorption is dominant for longer (picosecond) pulses. These inverse saturable absorption effects have important technological consequences, e.g. for the Q-switching dynamics of passively mode-locked lasers. A simple equation using only measurable SESAM parameters and including inverse saturable absorption is derived for the Q-switched modelocking threshold. We present various data and discuss the sometimes detrimental effects of this roll-over for femtosecond high repetition rate lasers, as well as the potentially very useful consequences for passively mode-locked multi-GHz lasers. We also discuss strategies to enhance or reduce this induced absorption by using different SESAM designs or semiconductor materials.
Journal of Crystal Growth, 2007
We report a monolithic broadband semiconductor saturable absorber mirror (SESAM) operating for 1025-1100 nm wavelength range with strain-compensated GaInAs/GaAsP quantum wells (QWs). By introducing tensile-strained GaAsP barriers, the compressive strain caused by the GaInAs QWs can be compensated and good quality QWs are obtained. Strain-compensated GaInAs/GaAsP QWs are grown on top of a GaAs/AlAs distributed Bragg reflector (DBR) to form the SESAM structure. The SESAM has a broad high-reflective stopband of about 120 nm and has been successfully used in passively modelocking a Nd:Gd 0.64 Y 0.36 VO 4 solid-state laser operating at 1064 nm wavelength. Optical pulses as short as 4.5 ps are generated with a peak power of 3.7 kW.
Theory of mode-locked semiconductor lasers with finite absorber relaxation times
Applied Physics Letters, 1997
We investigate the influence of a finite absorber relaxation time on passively mode-locked semiconductor lasers. We find that the mode-locking mechanism of Haus is surprisingly susceptible to small perturbations and small changes in the parameters. Even when the absorber relaxation time is much larger than the pulse duration, it typically is still short enough to be a crucial part of the physics of mode-locking. Allowing for a finite absorber relaxation time, we find that stable operation of a mode-locked semiconductor is possible over a wide range of parameters. We argue that the pulse duration is inversely proportional to the square root of the pulse energy. © 1997 American Institute of Physics. ͓S0003-6951͑97͒04615-9͔
Passively mode-locked Tm,Ho:YVO4 laser based on a semiconductor saturable absorber mirror
Chinese Optics Letters, 2012
We report the demonstration of passively continuous-wave mode-locking (CWML) of diode-pumped Tm,Ho:YVO4 laser using an InGaAs/GaAs multiple quantum-well (MQW) structure semiconductor as the saturable absorber. Stable mode-locking pulses at the central wavelength of 2 041 nm are obtained. The maximum output power is 151 mW. The pulse duration is 10.5 ps at the repetition rate of 64.3 MHz.
Journal of Physics D: Applied Physics, 2001
We demonstrate that ion implantation can be used for response time tailoring to create high-performance indium gallium arsenide (InGaAs) quantum well semiconductor saturable absorber mirrors (SESAMs). The design and manufacture of the SESAMs are described, and their nonlinear optical and temporal responses, relevant to the mode-locking of picosecond type pulses, are given. The implanted devices shown here have response times as short as 11 ps, compared with several hundred picoseconds without implantation. They have small non-bleachable losses and low saturation fluence (<20 µJ cm −2), allowing for operation far below the damage threshold. An implantation-and annealing-induced quantum well intermixing effect is shown to be present in the SESAMs, resulting in an energy shift in the excitonic feature. This effect can be taken into account in the SESAM design or minimized, if necessary. Using the SESAMs to mode-lock a low-power Nd:YVO 4 laser at 1064 nm, we have generated pulsewidths between 9 and 23 ps, depending on the cavity configuration and the SESAM used.
Theory of mode-locked lasers containing a reverse saturable absorber
IEEE Journal of Quantum Electronics, 1985
An analytic solution is presented for mode-locking a laser using a saturable absorber and reverse saturable absorber with long relaxation times compared to the temporal pulse widths. A reverse saturable absorber is a mater'ial with an excited-state absorption cross section larger than the ground-state absorption cross section, where increasing the incident light intensity increases the absorption. The reverse saturable absorber plays an important role in mode-locking laser materials where individual pulses cannot saturate the gain. A numerical example of mode-locking a CW alexandrite laser with a reverse saturable absorber and a saturable absorber is presented.
Applied Physics Letters, 2005
Metamorphic growth of InP on GaAs has been used to decrease the absorption recovery time of 1.55μm semiconductor saturable absorber mirrors. We show that the recovery time can be reliably controlled by changing the thickness of an InP “lattice reformation layer” grown between the GaAs-based distributed Bragg reflector and the active region. Semiconductor saturable absorber mirrors with a thickness of the InP reformation layer around 200 nm or smaller exhibit a recovery time short enough to reliably mode-lock fiber lasers.