Optimization of optical parametric chirped pulse amplification with different pump wavelengths

Optical parametric chirped pulse amplification with different pump wavelengths was investigated using LBO crystal, at signal central wavelength of 800 nm. According to our theoretical simulation, when pump wavelength is 492.5 nm, there is a maximal gain bandwidth of 190 nm centered at 805 nm in optimal noncollinear angle using LBO. Presently, pump wavelength of 492.5 nm can be obtained from second harmonic generation of a Yb:Sr₅(PO₄)₃F laser. The broad gain bandwidth can completely support ∼6 fs with a spectral centre of seed pulse at 800 nm. The deviation from optimal noncollinear angle can be compensated by accurately tuning crystal angle for phase matching. The gain spectrum with pump wavelength of 492.5 nm is much better than those with pump wavelengths of 400, 526.5 and 532 nm, at signal centre of 800 nm.     

Difference-frequency generation by mixing dual-wavelength pulses emitting from an electronically tuned Ti:sapphire laser

Broadly tunable difference-frequency generation (DFG) in AgGaS₂ was achieved by mixing dual-wavelength oscillating pulses from an electronically tuned Ti:sapphire laser with a two-frequency-driven acousto-optic device. Continuous tuning from 6.5 to 8.5 μm was achieved by simultaneous dual-wavelength-tuned DFG without crystal rotation. In the dual-pulse oscillation, the shorter and longer wavelength pulses were tuned from 700 to 775 nm and from 763 to 880 nm, respectively, while keeping the phase-matching relationship for DFG. When crystal rotation was adopted, however, the tunable output range was extended from 5.3 to 12 μm by tuning the longer wavelength pump pulse, while the shorter wavelength pulse was fixed. Received: 18 November 1998 / Revised version: 5 February 1999 / Published online: 26 May 1999     

Visible femtosecond pulses by second-harmonic generation of a cw mode-locked KTP optical parametric oscillator

Efficient generation of femtosecond pulses in the wavelength range from 520 to 675 nm by external frequency doubling the signal wave of a non-critically phase-matched picosecond KTP Optical Parametric Oscillator (OPO) in a non-critically phase-matched temperature tuned LiB₃O₅(LBO) crystal is demonstrated. An average power of the second harmonic as high as 310 mW at 575 nm was generated. In the absence of group velocity mismatch of LBO for a wavelength of the OPO at about 1.3 µm the minimum second-harmonic pulse width was 400 fs at 645 nm.     

A Theoretical Strategy to Generate an Isolated 80-Attosecond Pulse

Using a linearly polarized, phase-stabilized 2.66-femtosecond driving pulse of 400 nm central wavelength orthogonally combined with another linearly polarized long pulse of 800 nm central wavelength irradiating jointly on the helium atom, we demonstrate theoretically the generation of a clean isolated 80-attosecond pulse in the spectral region of 93-155 electron volts in a two-dimensional model.     

Optical limiting with higher fullerenes

Optical limiting has been investigated for higher fullerenes and compared with C₆₀. The transmission through an aperture placed after solutions of C₇₆, C₇₈, and C₈₄ in tetrahydronaphthalene was measured using Q-switched laser pulses with a wavelength of 532 nm and a pulse width of 8 ns FWHM. Unlike C₆₀, the transmission for these higher fullerene solutions decreased linearly with increasing optical pulse energy. We attribute the linearized optical limiting response to self-defocusing of the optical beam and the absence of excited-state absorption. The ground state absorption spectra for the higher fullerenes suggest their use for optical limiting in the near infrared, and the C₈₄-tetrahydronaphthalene solution was found to be an optical limiter at 1.064 m.     

Mechanism transition of self-pumped phase conjugation in KTa1 −xNbxO3:Fe crystals

Mechanism transitions of Self-Pumped Phase Conjugation (SPPC) with wavelength and doping concentration are observed in KTN:Fe (KTa_{1 –x} Nb _x O₃:Fe with _x = 0.48) crystals. The SPPC mechanism in KTN: Fe (0.4 wt. %) crystal transforms from Stimulated Photorefractive Backscattering and Four-Wave Mixing (SPB-FWM) to cat (or total internal reflection) as the wavelength increases from 514.5 nm to 620 nm. SPPC at 514.5 nm is formed with the cat mechanism in a 0.2 wt. % doped KTN:Fe crystal, while with the SPB-FWM mechanism in a 0.4 wt. % doped one. These mechanism transitions are discussed with respect to the dependence of the backscattering gain coefficient of the crystals on wavelength and doping concentration.     

Generation of dual wavelength ultrashort pulse outputs from a passive mode locked fiber ring laser

By incorporating two sections of polarization maintaining fibers in the passive mode locked fiber ring laser cavity, dual wavelength ultrashort pulse outputs, around 1558 nm and 1570 nm, having the same direction of polarization and pulse widths of 2.4 ps and 2.1 ps, respectively, were observed simultaneously.     

Elimination of cracking during UV laser ablation of SrTiO3 single crystals by employing a femtosecond laser

We have performed a comparative study of UV laser ablation of SrTiO₃ with nanosecond- and sub-picosecond sources, respectively. The experiments were performed with lasers at a wavelength of 248 nm and pulse durations of 34 ns and 500 fs. Femtosecond ablation turns out to be more efficient by one order of magnitude and eliminated the known problem of cracking of SrTiO₃ during laser machining with longer pulses. In addition, the cavities ablated with femtosecond pulses display a smoother surface with no indication of melting and well-defined, sharp edges. These effects can be explained by the reduced thermal shock effect on the material by using ultrashort pulses.     

High-power picosecond LiB3O5 optical parametric oscillators tunable in the blue spectral range

The paper reports on an experimental investigation and numerical analysis of noncritically and critically phasematched LiB₃O₅ (LBO) optical parametric oscillators (OPOs) synchronously pumped by the third harmonic of a cw diode-pumped mode-locked Nd:YVO₄ oscillator–amplifier system. The laser system generates 9.0 W of 355-nm mode-locked radiation with a pulse duration of 7.5 ps and a repetition rate of 84 MHz. The LBO OPO, synchronously pumped by the 355-nm pulses, generates a signal wave tunable in the blue spectral range 457–479 nm. With a power of up to 5.0 W at 462 nm and 1.7 W at 1535 nm the conversion efficiency is 74%. The OPO is characterized experimentally by measuring the output power (and its dependence on the pump power, the transmission of the output coupler and the resonator length) and the pulse properties (such as pulse duration and spectral width). Also the beam quality of the resonant and nonresonant waves is investigated. The measured results are compared with the predictions of a numerical analysis for Gaussian laser and OPO beams. In addition to the blue-signal output visible-red 629-nm radiation is generated by sum-frequency mixing of the 1.535-μm infrared idler wave with the residual 1.064-μm laser radiation. A power of 1.25 W of 1.535-μm idler radiation and 5.7 W of 1.064-μm laser light generated a red 629-nm output power of 2.25 W. Received: 2 February 2000 / Revised version: 28 July 2000 / Published online: 22 November 2000     

Broadband four-wave optical parametric amplification in bulk isotropic media in the ultraviolet

We report on four-wave optical parametric amplification of the ultrashort ultraviolet light pulses in bulk fused silica and CaF₂. Exact phase-matching in these isotropic media is achieved by means of non-collinear interaction with cylindrical beam focusing. Four-wave optical parametric amplifier efficiently operates in the UV spectral range with 1-ps laser pulses, delivering amplified signal energy exceeding 50 μJ using millijoule pump pulses in the visible (527 nm). Results of scanning of the parametric gain profile suggest that broad amplification bandwidth as wide as ∼20 nm (at FWHM) under these experimental settings is achieved, which might support amplification of sub-10-fs ultraviolet pulses with central wavelength around 330 nm. It is also shown experimentally and verified theoretically that the parametric gain profile exposes a distinct inhomogeneity and its bandwidth notably broadens due to effects of self- and cross-phase modulation imposed by the intense pump beam.     

Nonresonant tripling and sum-frequency mixing in Hg

Nonresonant frequency tripling and sum-frequency mixing of pulsed dye-laser radiation generates in Hg vapor continuously tunable coherent vuv radiation in the wavelength range _vuv=132-185nm. Laser pulse powers of 1–2 MW produce vuv light pulses of 0.6–1.5 W (2–4.8×10⁹ photons/pulse).     

Absorption bistability in evaporated ZnSex thin films

Intrinsic absorption bistability in ZnSe_1.36 thin films, produced by thermal evaporation is observed. The influence of laser pulse duration and resonator mirror reflectivity is studied experimentally and theoretically. Compared to ZnSe elements prepared by other methods, the evaporated films allow a longer operation wavelength of 514 nm, a low threshold power of 10 mW and a smaller element size below 10 m³.     

Low threshold, actively Q-switched Nd:YVO4 self-Raman laser and frequency doubled 588 nm yellow laser

We reported an actively Q-switched, intracavity Nd³⁺:YVO₄ self-Raman laser at 1176 nm with low threshold and high efficiency. From the extracavity frequency doubling by use of LBO nonlinear crystal, over 3.5 mW, 588 nm yellow laser is achieved. The maximum Raman laser output at is 182 mW with 1.8 W incident pump power. The threshold is only 370 mW at a pulse repetition frequency of 5 kHz. The optical conversion efficiency from incident to the Raman laser is 10%, and 1.9% from Raman laser to the yellow.     

Ytterbium femtosecond fiber laser without dispersion compensation tunable from 1015 nm to 1050 nm

We report on a widely tunable ytterbium fs-fiber laser without dispersion compensation. The all-normal dispersion laser contains a spectral filter for wavelength tuning and for generating additional amplitude modulation to support the nonlinear polarization evolution as mode-locking mechanism. By tilting the interference filter the center wavelength of the laser can be tuned from 1015 nm to 1050 nm with a pulse energy up to 2.0 nJ. The pulses can be dechirped externally to 108 fs.     

Attaining the wavelength range 189–197 nm by frequency mixing inβ-BaB2O4

Wavelengths in the range from 188.9 to 197 nm have been obtained by type-I sum frequency generation (SFG) in -BaB₂O₄. The fundamental beams were supplied by pulsed dye lasers one of which tuned between 780 and 950 nm and the other frequency-doubled at 497 nm. The possibility of shifting the excimer wavelength 248.5 nm to the excimer wavelength 193 nm has been demonstrated, replacing the frequency-doubled dye laser by KrF excimer lasers of different beam properties.     

Intra-cavity second harmonic generation with Nd:YVO4/BIBO laser at 542 nm

We report, for the first time, an efficient intra-cavity second-harmonic generation (SHG) at 1084 nm in a nonlinear optical crystal, BiB₃O₆(BIBO) at the direction of (θ, ?) = (170.1°, 90°), performed with a LD end-pumped cw Nd:YVO₄ laser. With 590 mW diode pump power, a continuous-wave (cw) SHG output power of 19 mW at 542 nm yellow-green color has been obtained using a 1.5 mm-thick BIBO crystal. The optical conversion efficiency was 3.22%. It was found that the output wavelength could be 532 nm, 537 nm or 542 nm according to regulating the angle of BIBO.     

Synchronously Pumped Femtosecond Optical Parametric Oscillator Based on MgO-Doped Periodically Poled LiNbO3

We report a femtosecond optical parametric oscillator based on MgO-doped PPLN synchronously pumped by a mode-locked Ti：sapphire laser. The wavelengths of the signal and idler are continuously tuned from 1100 to 1300hm and from 2080 to 2930nm, respectively, by changing the pump wavelength and the OPO cavity length. The maximum signal output power of 130mW at the wavelength of 1225nm is obtained, pumped by 900roW of 800hm laser radiation. This corresponds to a total conversion efficiency of 22.1%. The signal pulse duration is measured to be 167fs by intensity autocorrelation with chirped mirrors for intracavity dispersion compensation.     

High-peak power multi-wavelength picosecond pulses generated from a BaWO4 Raman-seeded optical parametric amplifier

We report the generation of high-peak power multi-wavelength picosecond laser pulses using optical parametric amplification (OPA) in BBO seeded with pulses generated in a 5-mm length BaWO₄ crystal by stimulated Raman scattering of 18-ps laser pulses at 532 nm. The maximum output energy of the amplified first-Stokes component at 559.7 nm was about 1.76 mJ. The corresponding maximum peak power, pulse duration and spectral line width were measured to be 117.3 MW, 15 ps and 18.0 cm⁻¹, respectively. The multi-wavelength picosecond laser pulses were in the visible and near infrared ranges. Using this Raman-seeded OPA technique, the beam quality of the stimulated Raman scattering pulses can be improved.     

Generation of continuous-wave coherent radiation tunable down to 190.8nm in β-BaB2O4

Continuous-wave coherent radiation tunable in the wavelength range 190.8–196.1 nm has been generated by sum-frequency generation in -BaB₂O₄. The fundamental beams were supplied by a Ti:Al₂O₃ laser and a frequency-doubled argon-ion laser.     

Development of a nearly transform-limited, low-repetition-rate, picosecond optical parametric generator

A low-repetition-rate (10-Hz), picosecond (ps) optical parametric generator (OPG) seeded at the idler wavelength with a high-power diode laser is demonstrated. The output of the OPG at ∼566 nm is amplified in dye cells, resulting in signal enhancement by more than three orders of magnitude. The nearly transform-limited beam at ∼566 nm has a pulsewidth of ∼170 ps, with an overall output of ∼2.3 mJ/pulse. The laser is tuned either by tuning the nonlinear crystal or the seed-laser current. The applications of such a simple, compact, high-performance, tunable ps laser system for linear and nonlinear spectroscopies are outlined.