Ultrafast lasers, which generate optical pulses in the picosecond and femtosecond range, have progressed over the past decade from complicated and specialized laboratory systems to compact, reliable instruments. Semiconductor lasers for optical pumping and fast optical saturable absorbers, based on either semiconductor devices or the optical nonlinear Kerr effect, have dramatically improved these lasers and opened up new frontiers for applications with extremely short temporal resolution (much smaller than 10 fs), extremely high peak optical intensities (greater than 10 TW/cm2) and extremely fast pulse repetition rates (greater than 100 GHz).

Recent developments in compact ultrafast lasers

Graphene is at the center of a significant research effort Near-ballistic transport at room temperature and high mobility make it a potential material for nanoelectronics Its electronic and mechanical properties are also ideal for micro- and nanomechanical systems, thin-film transistors, and transparent and conductive composites and electrodes Here we exploit the optoelectronic properties of graphene to realize an ultrafast laser A graphene-polymer composite is fabricated using wet-chemistry techniques Pauli blocking following intense illumination results in saturable absorption, independent of wavelength This is used to passively mode-lock an erbium-doped fiber laser working at 1559 nm, with a 524 nm spectral bandwidth and approximately 460 fs pulse duration, paving the way to graphene-based photonics

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Graphene Mode-Locked Ultrafast Laser

https://www.ulp.ethz.ch/content/dam/ethz/special-interest/phys/quantum-electronics/ultrafast-laser-physics-dam/publications_awards/publications/2006/248__PhysRep_429__67__2006_.pdf

Passively modelocked surface-emitting semiconductor lasers

A promising route to manufacturing portable (sub-)picosecond fibre lasers is to use a semiconductor saturable absorber mirror (SESAM). With SESAMs, the mode-locked regime can be achieved for different values of cavity dispersion for a broad spectrum ranging from 0.8 to 1.6 μm. The fibre lasers, characterized by a high efficiency and reliability and a small footprint, are very attractive for applications traditionally occupied by solid-state lasers. The broad fluorescence spectrum makes different fibre gain media attractive for tuneable and ultra-short-pulse sources. In this paper, we discuss recent advances in ultra-fast fibre lasers. We study the fundamental properties and technical challenges of mode-locked fibre lasers operating in the 0.9–1.6 μm range, and the methods to achieve high peak-powers from all-fibre devices. The key component is the SESAM, notably, a dilute nitride SESAM. The SESAM supplies a strong mechanism for picosecond pulse generation that is entirely self-starting for a wide range of cavity dispersion and ensures stability against Q-switched mode-locking. In particular, compact mode-locked lasers stabilized by near-resonant SESAMs can be realized in a short fibre cavity free from any dispersion compensator. An appropriate dispersion delay line at the output of the master source may be used for pulse clean-up. The high-quality pulses obtained can then be compressed using traditional methods, when the pulse first undergoes spectral enrichment via self-phase modulation in an auxiliary fibre and then gets compressed in a grating pair. The fibre laser is capable of efficient wavelength conversion via second harmonic generation in non-linear crystals. Using a periodically poled LiNbO3 crystal for frequency doubling, we produce sub-100 fs pulses at 0.8 μm with a 50% conversion efficiency.

https://iopscience.iop.org/article/10.1088/1367-2630/6/1/177/pdf

Ultra-fast fibre laser systems based on SESAM technology: new horizons and applications

The observation of coherent dynamics ensuing from the excitation of molecular systems by femtosecond laser pulses is at the heart of femtochemistry. The time-dependent evolution of coherent superpositions of quantum states, the physical basis for the observation of coherent dynamics and their manipulation are of central importance to coherent control of physicochemical processes. In the early days of femtochemistry, there was significant skepticism regarding the type of information that could be learned from spectroscopic experiments using very short pulses. There were arguments that one could infer the dynamics from frequency-resolved experiments and that the femtosecond experiments did not offer new information. It was also assumed that experiments with very short pulses would smear the available spectroscopic information because of their broad bandwidths. Approximately two decades after the initial experiments, it has become clear that femtosecond experiments have opened an extremely valuable window into the dynamic behavior of atomic and molecular systems that is influencing how we think about physics, chemistry, and biology. In particular, we highlight the fact that some of the highest resolution spectroscopic measurements being carried out employ femtosecond laser pulses. These experiments, specifically those taking advantage of rotational coherence, provide resolution that rivals microwave spectroscopy. The reason spectroscopic information is not lost in femtochemistry experiments is coherence, a property that can be manipulated to control physicochemical processes by a number of different approaches, which will be reviewed here. This review presents a summary of some of the most salient contributions to the field of coherent laser control from an experimentalist’s perspective. While a number of theoretical papers have made key contributions to the field, it is from the experimental successes, as well as failures, that we can best learn how to implement new strategies and develop future applications. Coherent laser control, in the context of this review, encompasses experiments in which the coherent properties of the laser and/or the molecule are required for controlling a particular physicochemical process. We distinguish for each of the experiments between coherence in the laser field(s), * To whom correspondence should be addressed. Phone (517) 3559715 (ext-315). Fax (517) 353-1793. E-mail dantus@msu.edu. 1813 Chem. Rev. 2004, 104, 1813−1859

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Experimental coherent laser control of physicochemical processes.

The use of a saturable absorber as a passive mode locker in a solid-state laser can introduce a tendency for Q-switched mode-locked operation. We have investigated the transition between the regimes of cw mode locking and Q-switched mode locking. Experimental data from Nd:YLF lasers in the picosecond domain and soliton mode-locked Nd:glass lasers in the femtosecond domain, both passively mode locked with semiconductor saturable absorber mirrors, were compared with predictions from an analytical model. The observed stability limits for the picosecond lasers agree well with a previously described model, while for soliton mode-locked femtosecond lasers we have developed an extended theory that takes into account nonlinear soliton-shaping effects and gain filtering. © 1999 Optical Society of America [S0740-3224(99)01001-2] OCIS codes: 140.3580, 140.4050, 140.3540, 140.7090.

/pdf/q-switching-stability-limits-of-continuous-wave-passive-mode-2p36n3urds.pdf

Q-switching stability limits of continuous-wave passive mode locking

The use of a saturable absorber as a passive mode locker in a solid-state laser can introduce a tendency for Q-switched mode-locked operation. We have investigated the transition between the regimes of cw mode locking and Q-switched mode locking. Experimental data from Nd:YLF lasers in the picosecond domain and soliton mode-locked Nd:glass lasers in the femtosecond domain, both passively mode locked with semiconductor saturable absorber mirrors, were compared with predictions from an analytical model. The observed stability limits for the picosecond lasers agree well with a previously described model, while for soliton mode-locked femtosecond lasers we have developed an extended theory that takes into account nonlinear soliton-shaping effects and gain filtering.

/pdf/q-switching-stability-limits-of-continuous-wave-passive-mode-1b26gdjvhp.pdf

We report for the first time on the efficient continuous-wave and mode-locked laser operation of a diode-pumped Yb:Gd0.64Y0.36VO4 laser. cw output power of 855 mW with a slope efficiency of 45% with respect to the absorbed pump power was demonstrated for the 2.1%-doped crystal. In mode-locked regime with SESAM as passive shutter pulses as short as 100 fs were obtained.

Spectroscopy and femtosecond laser performance of Yb3+ :Gd0.64Y0.36VO4 crystal

A near-field pump-probe system with nanometer-scale spatial and femtosecond temporal resolution allows us to measure complex spatiotemporal carrier diffusion dynamics in semiconductor nanostructures Single ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ quantum wells are patterned by nanometer-scale focused ion-beam (FIB) implantation, which introduces local carrier trapping The resulting carrier density gradients cause diffusion, which is directly observed by measuring carrier density variations in both time and space A comprehensive experimental study allows us to identify different diffusion regimes We find an initial diffusion regime, characterized by nonsinusoidal carrier profiles and spatially dependent temporal diffusion decay In a long-time regime, the carrier profile is quasisinusoidal and only weakly position-dependent temporal diffusion decay is observed

Direct experimental observation of different diffusive transport regimes in semiconductor nanostructures

We have studied the coherent emission from bulk semiconductors by spectrally resolved and spectrally integrated four-wave mixing (FWM) with broadband 16-fs pulses in the carrier density range from $1\ifmmode\times\else\texttimes\fi{}{10}^{16}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ to $6\ifmmode\times\else\texttimes\fi{}{10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ In GaAs, only continuum transitions are excited, while both excitonic and continuum transitions are excited in ${\mathrm{Al}}_{0.06}{\mathrm{Ga}}_{0.94}\mathrm{As}.$ The decay of the FWM signal for positive time delays unambiguously reflects the dephasing of the continuum, irrespective of the excitation of excitonic transitions. We find identical ultrafast sub-20-fs decay times of the coherent emission from continuum transitions in GaAs and ${\mathrm{Al}}_{0.06}{\mathrm{Ga}}_{0.94}\mathrm{As},$ independent of the excess excitation energy. These decay times depend only weakly on the carrier density for densities below ${10}^{17}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ The continuum dephasing is analyzed considering carrier-carrier and carrier-LO-phonon scattering in a relaxation rate approach. The excitonic transitions in ${\mathrm{Al}}_{0.06}{\mathrm{Ga}}_{0.94}\mathrm{As}$ dominate the FWM signal at negative time delays.

F. Morier-Genoud

Papers

Q-switching stability limits of continuous-wave passive mode locking

Q-switching stability limits of continuous-wave passive mode locking

Spectroscopy and femtosecond laser performance of Yb3+ :Gd0.64Y0.36VO4 crystal

Direct experimental observation of different diffusive transport regimes in semiconductor nanostructures

Ultrafast dephasing of continuum transitions in bulk semiconductors