E. Wintner

Operation of a femtosecond Ti:sapphire solitary laser in the vicinity of zero group-delay dispersion

We report the operating characteristics of a self-mode-locked Ti:sapphire solitary laser at reduced group-delay dispersion. The generation of asymptotically equal to 12.3 fs near-sech(2) optical pulses at 775 nm is reported, together with experimental evidence for the dominant role of third-order dispersion (TOD) as a limiting factor to further pulse shortening in the oscillator. At reduced second-order dispersion excessive residual TOD is shown to lead to dispersive wave generation, and the position of the dispersive resonance is used to determine the ratio of the net second- and third-order intracavity dispersions. Since the magnitude of TOD rapidly decreases with increasing wavelength in prism-pair dispersion-compensated resonators, the oscillator presented has the potential for producing sub-10-fs pulses in the 800-nm wavelength region.

Sub-20-fs, kilohertz-repetition-rate Ti:sapphire amplifier

A simple four-pass Ti:sapphire amplifier is seeded by sub-10-fs pulses generated from a mirror-dispersion-controlled Ti:sapphire laser. Pulses of 17-18-fs duration with energies up to 50 and 100 microJ have been produced at repetition rates of 2 and 1 kHz, respectively. Because of the absence of a pulse stretcher, this performance is achieved from an extremely compact system.

DIRECTLY DIODE-PUMPED TUNABLE CONTINUOUS-WAVE ROOM-TEMPERATURE CR4+:YAG LASER

We report what is to our knowledge the first directly diode-pumped tunable (over 120 nm) continuous-wave Cr(4+): YAG laser, operating near 1.5 microm . At room temperature the laser delivered as much as 200 mW of power at 4 W of absorbed pump power. We also report observation of slow laser output degradation and bleaching in highly concentrated crystals, which we suggest is due to a photorefractive phenomenon.

Femtosecond passive mode locking of a solid‐state laser by a dispersively balanced nonlinear interferometer

A Michelson interferometer containing a nonlinear fiber in one arm and dispersion control in the other arm has been used for passive mode locking of a continuous wave Nd:glass laser. We discuss scaling issues and demonstrate the usefulness of this technique by generating ≊300 fs pulses with only Pf≊15 mW of average power in the fiber and ≊100 fs pulses with a self‐starting threshold of Pf≊100 mW.

Hard-aperture Kerr-lens mode locking

Self-focusing by a Kerr nonlinearity in combination with an intracavity aperture creates a power-dependent loss in lasers, which has been used as a method for passive mode locking of lasers. An analytical treatment is presented that yields closed-form expressions for the modulation efficiency. Comparisons between analytical results and numerical calculations are performed. General features of this mode-locking technique are discussed, and a procedure for the optimization of hard-aperture Kerr-lens mode-locking performance is given.

Laser-induced optical breakdown applied for laser spark ignition

AbstractIn the present article, the experimental investigation of optical breakdown induced by ns/mJ pulses at two wavelengths,1064 nm and 532 nm, in air of atmospheric pressure is reported and discussed. The obtained breakdown thresholds werecompared with theory and are in good agreement. The generated plasmas have been characterized by their amount ofscattered laser light, energy transmission, and change of the transmitted temporal shape. Laser-induced plasmaformation in a gas, in air, also generates an acoustic pressure wave. The acoustic energy is compared to the laser pulseenergy and is found to be linearly dependent. Moreover, the frequency distribution of the characteristic acousticpressure wave was analyzed. The experiments described were accomplished in order to optimize a laser ignition systemwith regard to efficiency and costs. The laser system employed for these investigations is a compact high peak power,passively Q-switched, longitudinally diode-pumped solid-state laser. Such a “laser spark plug” should replaceconventional spark plugs in internal combustion engines because conventional ignition has reached its limits in termsof efficiency and durability. Thereby, a reduction of pollutant emission should also be feasible.Keywords: Acoustic pressure wave; Laser-induced plasma; Optical breakdown; Q-switched; Scattered laser light

Femtosecond solid-state lasers using Nd 3+ -doped mixed scandium garnets

The mode-locking features of a series of Nd3+-doped solid solutions of aluminum and gallium garnets are investigated, and the influence of multiline gain spectra on mode-locking performance is discussed. With an additive-pulse nonlinear Michelson interferometer used to mode lock the laser passively, pulses as short as 260 fs are obtained. The effect of interferometer detuning on the pulse characteristics is studied.

EFFICIENT CONTINUOUS-WAVE TEM00 AND FEMTOSECOND KERR-LENS MODE-LOCKED CR:LISRGAF LASER

Efficient high-power (900-mW) TEM(00) cw operation of a Cr:LiSrGaF laser pumped by a Kr(+) laser is demonstrated. The results of laser and spectroscopic analysis, including upconversion and excited-state absorption, are presented and used for the optimization of this laser. Kr(+)-laser-pumped mode-locked femtosecond operation (64 fs) was performed. Use of a modified resonator, which can decrease the threshold pump and intracavity power for Kerr-lens mode locking and increase the mode-locked output power (300 mW), is suggested. The inf luence of crystal axis misalignment on the tuning and mode-locking characteristics of the laser is studied.

Subpicosecond mode locking of a Nd3+-doped garnet laser.

We demonstrate subpicosecond pulse generation using a GSAG:YSGG:Nd3+ crystal. A dispersively balanced nonlinear Michelson interferometer has been used for self-starting mode locking to generate pulses of ∼0.5 ps with average output powers of as much as 190 mW.

Ultrashort pulse laser osteotomy

Laser treatment of bone tissue has already been the subject of many studies to find substitutes for mechanical instruments that are nowadays used in implantology and orthopaedics. Mainly lasers with pulse durations in the μs region have been tested leaving surface features that are not always satisfactory. Therefore, in the present study laser osteotomy has been performed with a 330 fs Yb:glass laser, λ = 1040 nm, at a pulse repetition rate of 1 kHz. For bovine spongiosa, compacta, and cartilage, the ablation thresholds as well as the ablation rates for various pulse energies have been determined. Additionally, quadratic areas have been ablated in bone tissue. The remaining morphology has been analyzed via scanning electron microscopy. Laser ablation has also been performed with an Er, Cr:YSGG laser, λ = 2780 nm, PRR = 20 Hz, τ ∼ 50 μs. The results of USPL and Erbium laser ablation are compared.