Femtosecond mode-locked semiconductor disk lasers (SDLs) have the potential to replace rather complex, expensive laser systems and to establish ultrashort-pulse applications outside of scientific laboratories. We report about almost Fourier-limited pulses with a duration close to 100 fs obtained in the single-pulse regime. The SDL cavity consisted of only three elements, an InGaAs/AlGaAs gain chip, a fast semiconductor saturable absorber mirror and an output coupler. The pulse in our mode-locked SDL was shaped mainly by the spectro-temporal behavior of saturable absorption and gain and the associated self-phase modulation. The group delay dispersion is small. Pulses as short as 107 fs were generated with a spectral width of 10.2 nm (FWHM), centered at 1030 nm. This results in a time-bandwidth product of ≈0.31, which is close to the transform-limit. The output power amounted to 3 mW at a pulse repetition rate of 5 GHz, corresponding to fundamental mode-locking. Harmonically mode-locked SDLs are capable of operating at much higher pulse repetition rates, which was also investigated. A maximum pulse repetition rate of 92 GHz was achieved while preserving the pulse duration shorter than 200 fs.

Ultrashort-pulse semiconductor disk lasers emitting around 1025 nm are presented. Pulse durations of 198 fs at 92 GHz and 107 fs at 5.1 GHz repetition rate were achieved by harmonic and fundamental mode-locking, respectively.

A semiconductor disk laser based on an InGaAs/AlGaAs quantum-well gain medium was mode-locked by a fast semiconductor saturable absorber mirror. By high-order harmonic mode-locking a 92 GHz pulse train was obtained with a pulse duration of <200 fs. In order to achieve fundamental mode-locking, too strong saturation of the semiconductor elements had to be avoided. In a single-pulse regime, pulses shorter than 110 fs were generated at a wavelength of 1030 nm.

A terahertz time-domain spectroscopy (THz-TDS) system using an optically pumped semiconductor disk laser and high-speed asynchronous optical sampling is reported. The combination of these techniques holds considerable promise towards a compact and low-cost implementation of THz-TDS. The spectrometer offers a 333 ps time delay window scanned at 10 kHz and delivers more than 1.2 THz spectral coverage at a data acquisition time of one minute. As a proof-of-principle experiment, a 0.8 THz resonance of a frequency-selective surface structure was measured.

Almost chirp-free pulses with a duration of 190 fs were achieved from a mode-locked semiconductor disk laser (SDL) emitting at approximately 1045 nm. Pulse shaping was different from the soliton-like mode-locking process known from lasers using dielectric gain media; passive amplitude modulation provided by a fast saturable absorber was essential. The spectrum of the absorber had to be matched to the gain spectrum within a few nm. A tapered diode amplifier was demonstrated to be a device for both picking and amplifying SDL pulses. The pulse repetition rate of the SDL output was reduced from 3 GHz to 47 MHz.

Optically-pumped semiconductor disk lasers (SDLs) promise to be versatile femtosecond sources, because they can be tailored for almost any wavelength. Very recently, by passive mode-locking of SDLs with a semiconductor saturable absorber mirror (SESAM), pulse durations as short as 290 fs and 260 fs were demonstrated in the 1-mum wavelength range. Here, we investigate the laser parameters important for short-pulse performance and present 190-fs pulses from a diode-pumped InGaAs/AlGaAs laser emitting around 1045 nm. By this, we improved the record for semiconductor lasers without external pulse compression. Furthermore, we showed the feasibility of a new tapered diode amplifier with ultrafast electrical pumping for pulse amplification and picking, giving free choice of pulse repetition frequency.

The femtosecond regime of mode-locked InGaAs/AlGaAs disk lasers was investigated, resulting in almost chirpfree sub-220-fs pulses. Pulse picking using a tapered diode amplifier is demonstrated, reducing the pulse rate from 3 GHz to 47 MHz.

The femtosecond laser performance of an optically pumped InGaAs-AlGaAs disk laser emitting around 1.04 µm was studied. Using a saturable absorber with a surface-near quantum well, 190-fs-pulses were generated.

We report the shortest pulses (290 fs) obtained directly from semiconductor lasers. These were achieved using a passively mode-locked semiconductor disk laser with a graded-gap barrier design in the gain section operating near 1036 nm.

A passively mode-locked semiconductor disk laser employing a graded-gap-barrier design in the gain section is presented. The all-semiconductor laser generates transform-limited pulses as short as 290 fs at 1036 nm.

Transform-limited pulses as short as 290 fs at 1036 nm are generated by a diode-pumped semiconductor disk laser. The all-semiconductor laser employs a graded-gap-barrier design in the gain section. A fast saturable absorber mirror serves as a passive mode-locker. No further elements for internal or external dispersion control are required.

Among the crystalline rare earth laser hosts the isotropic sesquioxides Sc2O3, Y2O3, and Lu2O3 (cubic bixbyite structure) are known for their superior thermo-mechanical properties. Their thermal conductivity considerably exceeds that of Y3Al5O12 (YAG). Their low phonon energy ensures large energy storage times by minimizing non-radiative relaxation processes. Yb-doped sesquioxides exhibit somewhat broader absorption and emission bandwidths than Yb:YAG which is advantageous for uncritical diode laser pumping and short pulse generation. The splitting of the lower Yb3+ manifold is also larger which is important in the quasi-four-level operation scheme. Solid solutions with the isostructural Yb2O3 are possible but the observed strong lifetime quenching makes the sesquioxide hosts more suitable for laser geometries that profit from relatively low Yb concentrations. Lu2O3 is the host whose thermal conductivity is least affected by Yb-doping. The high melting point (above 2400°C) makes it difficult to grow the sesquioxides from the melt. Recently, the use of the heat-exchanger-method (HEM) allowed to considerably enhance the optical quality of the grown crystals and the available single crystal size. Here we review the properties and present laser results obtained recently with Yb-doped sesquioxide crystals in the continuous-wave (cw) and mode-locked (picosecond and femtosecond) regimes using both Ti:sapphire and diode-laser pumping. In the cw regime optical-to-optical efficiency of 62.2% and slope efficiency of 72.7% were reached with Yb:Sc2O3 operating at 1041.6 nm. Passive mode-locking of both Yb:Sc2O3 and Yb:Lu2O3 was achieved by semiconductor saturable absorber mirrors. Pulse durations of the order of 200 fs were obtained with intracavity dispersion compensation.

Passive mode locking of the Yb:Sc2O3 laser is demonstrated. We investigate the laser performance with Ti:sapphire and diode-laser pumping. The laser is mode locked by use of a semiconductor saturable-absorber mirror and emits as much as 0.8 W of power in the picosecond range with a pump efficiency as high as 47%. With dispersion compensation, pulses as short as 230 fs for an average power of 0.54 W are obtained at 1044 nm. This is, to our knowledge, the first femtosecond oscillator based on an Yb-doped sesquioxide crystal.

The growing interest on Yb-doped lasers has been underlined by creating new active materials with Yb3+ as a dopant. The anisotropic monoclinic tungstate crystals KY(WO4)(2) and KGd(WO4)(2) used as hosts for Yb3+ provide larger absorption and emission cross sections and smaller quantum defect than YAG. Especially for the thin disk laser concept highly doped materials with short absorption lengths are appropriate. We present continuous-wave (cw) lasing results with a 100% Yb-doped KYb(WO4)(2) (KYbW), the first stoichiometric cw laser based on Yb3+ as an active ion.The cw laser experiments were performed with a 125-mum-thin KYbW sample. The one side high-reflective-coated KYbW crystal was positioned at one end of a V-type laser cavity and fixed on a new type of a holder, a "laminar laser mount", which enables direct water cooling of the pumped region of the laser crystal. A home made cw Ti:Sapphire laser served as the pump source.CW laser oscillation was observed at a pump threshold (lambda(pump) = 1025 nm) of 70 mW with a slope efficiency of 21% with respect to the absorbed pump power at room temperature. The maximum output power amounted to 20 mW for a 0.3% outcoupling transmission. The emission spectrum was centered at lambda(L)=1068 nm.

The smallest quantum defect for an optically pumped laser crystal could be demonstrated at room temperature, using a 125 mum-thin platelet of KYb(WO4)(2), a stoichiometric Yb laser material. While pumping at 1025 nm, lasing occurred at 1042 nm which corresponds to a quantum defect of only 1.6%.

The smallest quantum defect (1.6%) for a laser crystal is demonstrated with a 125 /spl mu/m-thin plate of stoichiometric KYb(WO/sub 4/)/sub 2/. Pumped at 1025 nm, it emitted at 1042 nm.