Generation Of High-energy Pulses Research Articles

Chirped-pulse oscillators for the generation of high-energy femtosecond laser pulses

This paper reports on a novel approach for producing high energy femtosecond pulses without external amplification. The so-called chirped-pulse oscillator (CPO) concept is based on an extended-cavity oscillator, operating at small net positive intracavity group delay dispersion (GDD), over a broad spectral range by the use of chirped multilayer mirrors. The resultant chirped picosecond pulses are compressed by a dispersive delay line external to the laser cavity. Utilizing this technique, sub-30 fs pulses with an energy exceeding 200 nJ at a repetition rate of 11 MHz were produced. The demonstrated peak power in excess of 5 MW is the highest ever achieved from a cw-pumped laser and is expected to be scaleable to tens of megawatts by increasing the pump power and/or decreasing the repetition rate. The demonstrated source allows micromachining of any materials under relaxed focusing conditions.

Broadband nonlinear optical conversion of a high-energy diode-pumped picosecond laser

We report on a high-energy picosecond pulse generation out made of a simple and inexpensive all-solid-state diode-pumped oscillator. The system produces 200 nJ, 7-ps pulses with an average power as high as 3 W, using laser components with a total price of all opto-mechanical components of about $10,000. High-power broadband continuum generation is demonstrated in a specially selected single mode GeO 2-doped fiber.

90-fs stretched-pulse ytterbium-doped double-clad fiber laser.

We report ultrashort, high-energy pulse generation from a side-pumped Yb-doped double-clad fiber laser. The laser is operating in the stretched-pulse regime. It directly generates 4.8-ps, 5-nJ pulses that are extracavity compressed to 90 fs.

High-energy sub-picosecond pulse generation from 3 to 20 μm

We have produced sub-picosecond pulses in the wavelength range 3–20 μm with energies as high as 2 μJ, through difference-frequency mixing in the crystal GaSe. Input beams for the non-linear mixing process came from either a regenerative amplifier operating in two-color mode, due to the spectral shaping of its injection beam, or an optical parametric amplifier (OPA). The first method was straightforward to implement and provided easy access to the wavelength range 10–20 μm. The intermediate OPA stage, though technically more involved, allowed higher input beam irradiances and resulted in shorter duration MIR pulses, greater conversion efficiency and access to the MIR region between 3 and 10 μm.

High-energy pulse generation from solid-state ultraviolet lasers using large Ce:fluoride crystals

Abstract A large Ce3+:LiCaAlF6 (Ce:LiCAF) crystal with 15 mm diameter was grown successfully by the Czochralski method. Owing to its large size, 60 mJ, 289 nm pulses were generated directly from a quasi-coaxially pumped Ce:LiCAF laser. In addition, a new noncollinear Brewster-angle-pumping disk oscillator scheme was demonstrated for further output-energy scaling. An ultraviolet solid-state Ce3+:LiLuF4 (Ce:LLF) laser which was pumped transversely by a KrF excimer laser with the repetition rate of 1 Hz produced a 27 mJ, 309 nm pulse using a large Ce:LLF crystal which was grown by the Czochralski method, and the slope efficiency was approximately 17%.

Generation of high-energy femtosecond pulses in multimode-core Yb-fiber chirped-pulse amplification systems

220-fs pulses with energies of ~100microJ have been generated by use of two different configurations of diode-pumped Yb-fiber chirped-pulse amplification systems. Energy scaling was demonstrated with 25-microm -core diameter fibers, in which stable diffraction-limited output (M(2)~1.1) was achieved. A two-stage fiber-amplifier system produced average powers of up to 5.5 W at ~1- MHz pulse-repetition rate. A double-pass configuration provided 53-dB gain in a single Yb-fiber amplifier stage, thus eliminating the necessity for multiple amplification stages as well as the need for using polarization-preserving fibers.

Generation of 90-nJ pulses with a 4-MHz repetition-rate Kerr-lens mode-locked Ti:Al_2O_3 laser operating with net positive and negative intracavity dispersion

We demonstrate the generation of high-energy pulses by using a low-repetition-rate Kerr-lens mode-locked laser. Repetition rates as low as 4 MHz were achieved with a long, multiple-pass cavity and a semiconductor saturable Bragg reflector. The laser generated pulses of 55-fs duration with a pulse energy of 48 nJ when it was mode locked in the net negative dispersion regime. Mode locking in the positive dispersion regime reduces instabilities and enables pulses to have durations of 80 fs and energies as high as 90 nJ. This is, to our knowledge, the highest pulse energy and the lowest repetition rate ever generated directly from a femtosecond laser resonator without cavity dumping.

Adaptive pulse compression for transform-limited 15-fs high-energy pulse generation

We demonstrate the use of a deformable-mirror pulse shaper, combined with an evolutionary optimization algorithm, to correct high-order residual phase aberrations in a 1-mJ, 1-kHz, 15-fs laser amplifier. Frequency-resolved optical gating measurements reveal that the output pulse duration of 15.2 fs is within our measurement error of the theoretical transform limit. This technique significantly reduces the pulse duration and the temporal prepulse energy of the pulse while increasing the peak intensity by 26%. It is demonstrated, for what is believed to be the first time, that the problem of pedestals in laser amplifiers can be addressed by spectral-domain correction.

Experimental investigation of a Q-switched triple contact InGaAs bow-tie diode laser

In this study the authors investigate high-energy picosecond pulse generation in a three contact two quantum well (QW) p-doped InGaAs bow-tie diode laser using a passive Q-switching technique. Picosecond duration pulses with pulse energies of 39 pJ and peak powers in excess of 700 mW are obtained from the device in a well defined single lobed far-field. The pulses have typically 45 to 55 ps durations (FWHM). Unwanted tails can be prevented by adjusting the reverse-bias voltage.

Nonlinear source for the generation of high-energy few-cycle optical pulses

We investigate the evolution of optical pulses in a hollow waveguide filled with noble gas at pulse intensities for which tunnel ionization dominates the nonlinear response of the gas. A numerical analysis reveals that the spectral chirp generated by the plasma nonlinearity is to a good approximation linear over the whole pulse spectrum and can be compensated in a dispersive delay line. Our calculations predict the generation of 3-4-fs optical pulses with energies of a few milijoules. To our knowledge, these energies are an order of magnitude greater than the pulse energies that have been realized to date in hollow-fiber compressors based exclusively on the nonlinear Kerr effect.

Effects of carrier cooling and carrier heating in saturation dynamics and pulse propagation through bulk semiconductor absorbers

Numerical modeling has shown that carrier cooling and carrier heating strongly influence saturation dynamics and pulse shaping in bulk semiconductor absorbers. With no electric field in the absorbing region, carrier cooling leads to strong additional fast saturation of absorption. The saturation causes a substantial decrease in the saturation energies for subpicosecond pulses in comparison with picosecond pulses. Comparison of bulk and quantum-well absorbers shows that fast saturation can be stronger in a bulk absorber, so bulk saturable absorbers may be interesting for usage in mode-locked solid-state lasers. Applying a nonzero electric field to a bulk absorber leads to strong carrier heating, which in turn suppresses absorption saturation. In this ease, transition to absorption saturation involves new mechanisms such as screening of the electric field by photogenerated carriers, as well as carrier cooling due to carrier-phonon interaction and by generated cold carriers. Carrier heating by the electric field causes the saturation energy of the absorber to increase with the applied electric field. The increased saturation energy allows one to shorten high-energy picosecond and subpicosecond pulses without increasing the length of the saturable absorber, which could be useful for the generation of high energy pulses with mode-locked and Q-switched semiconductor lasers.

Ultrashort pulse-train instabilities in additive-pulse mode-locked lasers

Numerical studies of nonlinear dynamics of pulse trains in an additive—pulse mode—locked laser are presented including diagrams of dynamical regimes,Lyapunov’s exponents and bifurcation diagrams. Period doubling sequences, period—3 regimes, hysteresis, and hyperchaos were observed. Regions of high—energy pulse generation and transformations of the period regimes regions with variation of values of coupling mirror reflection are found.

Generation of high-energy (0.3 μJ) short pulses (>400 ps) from a gain-switched laser diode stack with subnanosecond electrical pump pulses

Record pulse energy (E/spl sim/0.3 /spl mu/J) is reported for a gain-switched laser diode stack with subnanosecond electrical pump pulses. Pulsewidths near 100 ps are seen to be feasible. A detailed time-resolved analysis of emitted near-field patterns is presented, which provides guidelines for further improvements in time performances. A stack design for pulsed laser diodes of high energy is discussed.

Nonlinear chirp compensation in high-power broad-spectrum pulses from single-stripe mode-locked laser diodes

We report on the generation of ultra-short high-energy pulses from extended-cavity mode-locked laser diodes by using single-stripe AlGaAs laser devices of long cavity length (1 and 2 mm). The pulse energy is shown to increase with the laser diode length while the spectral width of emitted pulses is decreased in the same time. Record pulse energies of /spl ap/50 pJ are obtained from 2 mm long lasers and super-broad mode-locked spectra of /spl ap/20 mm are achieved with 1 mm long lasers. Strongly nonlinear chirps are always observed in the case of mode-locked pulses whose spectral width exceeds 10 mm. After quadratic chirp compensation, 160 fs pulses are obtained with peak power larger than 100 W. These performances are believed to be the best ever reported for mode-locked single-stripe laser diodes without external amplification. >

Generation of high-energy subnanosecond light pulses through direct current modulation of heterostructure lasers

This paper reports a study of the energy characteristics of highly efficient injection lasers with a narrow active channel based on separate-confinement heterostructures in (GaAl)As and (InGa)PAs systems. The lasers were pumped by current pulses 0.5 ns long with a height far above the lasing threshold (by as much as a factor of 1000). Limitations are imposed on the energy of the output pulses by nonlinear internal losses and degradation of the laser diodes.

Generation of high-energy subnanosecond pulses by solid-state lasers

Generation of high-energy subnanosecond pulses by solid-state lasers