Pancho Tzankov

Ultrabroadband continuum amplification in the near infrared using BiB3O6 nonlinear crystals pumped at 800 nm.

Ultrabroadband parametric amplification of a white-light continuum in the near IR (approximately 100 THz, 1.2-2.4 microm) is demonstrated in BiB3O6 pumped by 45 fs long pulses at 800 nm at a repetition rate of 1 kHz. The energy obtained with a 5 mm thick crystal reached 50 microJ, corresponding to external conversion efficiency of 20%.

Effective second-order nonlinearity in acentric optical crystals with low symmetry

We derive explicit expressions in the frame of the optical indicatrix for the second-order effective nonlinearity in biaxial crystals with point groups 2, m, and 1, governing the conversion efficiency in three-wave nonlinear optical interactions. The tabulated expressions for the monoclinic symmetry classes 2 and m are valid for all possible orientations of the optical indicatrix relative to the crystallographic frame and for propagation along an arbitrary direction outside the principal planes. They can be used for direct estimation of the effective nonlinearity in the same frame where the phase-matching loci are calculated. The relevant properties and conventions used for the newly emerging acentric monoclinic crystals belonging to the borate family are summarized and tabulated. The derivations are expected to help establish adherence to uniform nomenclature and conventions for these novel inorganic nonlinear crystals, and to eliminate ambiguity and increasing confusion in the literature and in the industrial specifications. The general expressions for the effective nonlinearity are reduced for triclinic crystals of point group 1 to simplified forms in the principal planes.

Tunable femtosecond pulses in the near-ultraviolet from ultrabroadband parametric amplification

Using an ultrabroadband amplification technique in a β-barium borate noncollinear optical parametric amplifier, pumped by the third harmonic of a 1 kHz Ti:sapphire laser, we generate tunable femtosecond pulses in the range of 335–480 nm with energies of a few hundred nJ. The developed setup is an amplification source with a bandwidth of more than 200 THz and provides femtosecond pulses in the near-ultraviolet spectral range using coherent amplification. Parts of the amplified white-light continuum spectrum were compressed to 24–35 fs using a prism pair. Further improvements could make it possible to generate tunable ultraviolet pulses as short as 4–5 fs.

High-power Femtosecond Optical Parametric Amplification at 1 kHz in BiB(3)O(6) pumped at 800 nm.

Substantial power scaling of a travelling-wave femtosecond optical parametric amplifier, pumped near 800 nm by a 1 kHz Ti:sapphire laser amplifier, is demonstrated using monoclinic BiB(3)O(6) in a two stage scheme with continuum seeding. Total energy output (signal plus idler) exceeding 1 mJ is achieved, corresponding to an intrinsic conversion efficiency of approximately 32% for the second stage. The tunability extends from 1.1 to 2.9 microm. The high parametric gain and broad amplification bandwidth of this crystal allowed the maintenance of the pump pulse duration, leading to pulse lengths less than 140 fs, both for the signal and idler pulses, even at such high output levels.

Efficient 1 kHz femtosecond optical parametric amplification in BiB 3 O 6 pumped at 800 nm

We demonstrate efficient operation of a tunable femtosecond optical parametric amplifier based on BiB(3)O(6) pumped at 800 nm by a 1 kHz Ti:sapphire regenerative amplifier. The idler wavelength coverage extends to beyond 3 mum and the pulse duration at this wavelength is of the order of 110 fs. This new nonlinear borate crystal offers exceptionally high nonlinearity, making it a very promising candidate for power scaling of such frequency converters in the near-IR.

Generation and compression of femtosecond pulses in the vacuum ultraviolet by chirped-pulse four-wave difference-frequency mixing

Ultrashort vacuum ultraviolet pulses at 161 nm with energies above 1 muJ were generated by chirped-pulse four-wave difference-frequency mixing in argon-filled aluminum-coated hollow waveguide. The pulses were compressed to 140-fs pulse duration by material dispersion.

Optical parametric generation of high-energy femtosecond pulses in the 1-3 μm spectral range using BiB3O6

We analyze the phase-matching properties of the monoclinic nonlinear crystal BiB3O6 (BIBO) for optical parametric amplification of femtosecond pulses when pumped near 800 nm by Ti:sapphire based laser systems. BIBO possesses higher figure of merit than &bgr;-BaB2O4 (BBO) and extremely large parametric gain bandwidth for collinear interaction. Experimentally, we compare type-II BIBO and BBO in a double pass optical parametric amplifier (OPA), pumping by amplified 80-fs pulses near 800 nm at a repetition rate of 1 kHz. The conversion efficiency obtained with BIBO is higher and a total energy output (signal + idler) of about 80 &mgr;J is obtained in the plateau region of the tunability curve (1-3 &mgr;m) with an uncoated sample, for a total pump energy of 375 &mgr;J. Shorter pulse durations were obtained with BIBO: e.g. 120 fs (FWHM) near 3 &mgr;m for the idler pulses. Substantial power scaling of such a femtosecond OPA is possible using a large aperture BIBO crystal in the second stage and we demonstrate a total energy output (signal + idler) exceeding 1 mJ, corresponding to an intrinsic conversion efficiency of ≈32% for the second stage, using a specially designed high-power Ti:sapphire pump system operating at 1 kHz. The tunability extends in this case from 1.1 to 2.9 &mgr;m. The high parametric gain and broad amplification bandwidth of type-I BIBO allow the maintenance of the pump pulse duration, leading to pulse lengths less than 140 fs, both for the signal and idler pulses, even at such high output levels.

Spatio-temporal characterization of the signal pulse-shortening in Type II optical parametric amplifier using BBO and BIBO crystals

Comparison of the performance of an optical parametric amplifier is presented using BBO or BIBO crystals in Type II. The spatio-temporal effect of the parametric pulse-shortening is experimentally investigated with respect to the signal wavelength.

The application of the monoclinic BiB3O6 nonlinear crystal in ultrafast laser technology

BiB3O6 (BIBO), the first low-symmetry (monoclinic class 2) inorganic nonlinear crystal that became commercially available, possesses some unique advantages for applications in ultrafast laser technology which are primarily related to its dispersive properties. In the present paper, these properties are analyzed in more detail and compared with other crystals. Of special interest is the pumping of this material near 800 nm for broadband parametric amplification in the near-infrared between 1.15 and 2.4 μm. We present experimental results on generation and amplification of ultrabroadband femtosecond continua in this spectral range using amplified Ti:sapphire lasers as pump sources.

Generation of High Power Picosecond Pulses by Passively Mode-Locked Nd: Yag Laser Using Frequency Doubling Mirror

In the last few years frequency doubling nonlinear mirror (FDNLM) consisting of a crystal for second harmonic generation and a dielectric mirror, placed at specific distance, was used as a means of self-mode-locking [1, 2, 3] or of pulse shortening [4, 5, 6] in pulse and CW pumped lasers. The results obtained so far for pulse pumped lasers are for the case when FDNLM operates only as an amplitude modulator (so called nonlinear mirror technique [1,2,5]). In this case the doubling in the nonlinear crystal is made with exact phase matching conditions and the dielectric mirror needs to be a dichroic mirror, i.e. to have comparatively low reflection coefficient at the fundamental frequency. These lasers suffer from two main drawbacks. Firstly the duration of the dichroic mirror output pulse is several times longer than the duration of the pulse traveling through the laser cavity [7] and secondly the laser suffers pulse parameter fluctuations [1,2,5]. Here we described a self mode-locked pulsed laser which has the aforementioned drawbacks overcame. The synchronization of modes in it is made by phase shift FDNLM, the latter operating by cascaded second order processes.