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

Sub-three-cycle pulses at 2 µm from a degenerate optical parametric amplifier

In this work we present a compact two-stage optical parametric amplifier (OPA) pumped at degeneracy by the fundamental of a Yb:KGW laser system. The output pulses span from 1.7 to 2.5 µm (120-176 THz) and are compressed to a sub-20 fs duration. This parametric amplifier exploits the broad phase-matching bandwidth at the degeneracy point in bismuth triborate (BiBO) and periodically poled lithium tantalate (PPLT). The result drastically expands the availability of ultrashort pulses with few-microjoule energy from near-infrared (NIR) to even longer wavelengths in the mid-infrared (MIR) spectral region.

Green-Yellow-Orange-Red Spectral Range with Sum-Frequency Generation Using BIBO Crystal Pumped with an Optical Parametric Amplifier

In this letter, we show the broadband sum-frequency generation (SFG) in the Green-Yellow-Orange-Red spectral range using bismuth triborate, BiB3O6 crystal (BIBO) as a nonlinear material. We perform a noncollinear phase-matching configuration within the BIBO crystal using the remaining light behind the second harmonic generation stage and the infrared idler of an optical parametric amplifier (OPA). The obtained mixing radiation of ultrafast light sources to generate femtosecond pulses across the 520.5 to 742.5 nm region is observed. The SFG spectrum from a single-pass cross-correlation intensity over such visible range is shown. The SFG wavelengths as a function of the tunable wavelength idler OPA agree with the expectations of the parametric conversion condition and open the door to practical multi-beam or multi-color sum-frequency generators.

High-efficiency optical parametric chirped-pulse amplifier in BiB₃O₆ for generation of 3 mJ, two-cycle, carrier-envelope-phase-stable pulses at 1.7 μm

We produce a 3 mJ, two-cycle (11.4 fs), 1 kHz, carrier-envelope phase (CEP)-stable laser source at 1.7 μm via a three-stage Ti:sapphire-pumped optical parametric chirped-pulse amplifier in BiB3O6. We achieve a pump-to-signal conversion efficiency of 18% in the last stage, which is, to the best of our knowledge, the highest yet achieved for near-octave bandwidth amplification. A f-to-2f measurement shows a CEP instability of 165 mrad over 1 h. This is an ideal light source for generating isolated attosecond pulses in the soft x-ray region.

Carrier-envelope phase-dependent high harmonic generation in the water window using few-cycle infrared pulses

High harmonic generation (HHG) using waveform-controlled, few-cycle pulses from Ti:sapphire lasers has opened emerging researches in strong-field and attosecond physics. However, the maximum photon energy of attosecond pulses via HHG remains limited to the extreme ultraviolet region. Long-wavelength light sources with carrier-envelope phase stabilization are promising to extend the photon energy of attosecond pulses into the soft X-ray region. Here we demonstrate carrier-envelope phase-dependent HHG in the water window using sub-two-cycle optical pulses at 1,600 nm. Experimental and simulated results indicate the confinement of soft X-ray emission in a single recombination event with a bandwidth of 75 eV around the carbon K edge. Control of high harmonics by the waveform of few-cycle infrared pulses is a key milestone to generate soft X-ray attosecond pulses. We measure a dependence of half-cycle bursts on the gas pressure, which indicates subcycle deformation of the waveform of the infrared drive pulses in the HHG process.

The higher-harmonic generation of laser pulses is used to achieve short-wavelength attosecond pulses for ultrashort experiments, but has been limited in the achievable energy. Here, Ishii et al. develop a scheme to break this barrier and to achieve photon energies higher than the carbon K edge of about 284 eV.

Exploring constrained quantum control landscapes

The broad success of optimally controlling quantum systems with external fields has been attributed to the favorable topology of the underlying control landscape, where the landscape is the physical observable as a function of the controls. The control landscape can be shown to contain no suboptimal trapping extrema upon satisfaction of reasonable physical assumptions, but this topological analysis does not hold when significant constraints are placed on the control resources. This work employs simulations to explore the topology and features of the control landscape for pure-state population transfer with a constrained class of control fields. The fields are parameterized in terms of a set of uniformly spaced spectral frequencies, with the associated phases acting as the controls. This restricted family of fields provides a simple illustration for assessing the impact of constraints upon seeking optimal control. Optimization results reveal that the minimum number of phase controls necessary to assure a high yield in the target state has a special dependence on the number of accessible energy levels in the quantum system, revealed from an analysis of the first- and second-order variation of the yield with respect to the controls. When an insufficient number of controls and/or a weak control fluence are employed, trapping extrema and saddle points are observed on the landscape. When the control resources are sufficiently flexible, solutions producing the globally maximal yield are found to form connected "level sets" of continuously variable control fields that preserve the yield. These optimal yield level sets are found to shrink to isolated points on the top of the landscape as the control field fluence is decreased, and further reduction of the fluence turns these points into suboptimal trapping extrema on the landscape. Although constrained control fields can come in many forms beyond the cases explored here, the behavior found in this paper is illustrative of the impacts that constraints can introduce.

Sub-two-cycle, carrier-envelope phase-stable, intense optical pulses at 1.6 μm from a BiB3O6 optical parametric chirped-pulse amplifier

We report on the generation of 9.0 fs, 550 μJ, carrier-envelope phase (CEP)-stabilized optical pulses around 1.6 μm at 1 kHz. Few-cycle IR pulses are obtained from a BiB(3)O(6) optical parametric chirped-pulse amplifier. The amplification of nearly octave-spanning ultrabroad pulses without spectral broadening results in good stability in output energy (0.85% rms) and CEP (160 mrad rms). We observed high harmonics in the water window from a neon cell that corresponds to a laser intensity of 4.1×10(14) W/cm(2).

High-average-power, carrier-envelope phase-stable, few-cycle pulses at 2.1 μm from a collinear BiB3O6 optical parametric amplifier

We generate self-carrier-to-envelope phase-stable, 630 μJ pulses, centered at 2.1 μm, with 42 fs (6 cycle) duration based on collinear optical parametric amplification in BiB(3)O(6) at 3 kHz. These pulses are generated through a traveling wave amplifier scheme, and the bandwidth supports 28 fs (4 cycle) pulse duration. Carrier-to-envelope phase stability was measured to be 410 mrad over 10 min or 260 mrad over 35 s.

Ultra-broadband sum-frequency vibrational spectrometer of aqueous interfaces based on a non-collinear optical parametric amplifier

We describe an ultrabroadband IR-visible sum-frequency (SF) setup that allows simultaneous acquisition of the entire vibrational spectrum of water molecules at mineral surfaces in the OH stretching region without ever tuning the IR laser pulses. Our newly developed 800-nm pumped noncollinear optical parametric amplifier (NOPA) generates broadband mid-IR pulses (~1800-3500 nm, or ~2900 - 6000 cm-1) with bandwidths >600 cm-1 at half-maximum at near 3500 cm-1. Using the ultra-broadband IR NOPA, we constructed a sum-frequency vibrational spectrometer that allowed the acquisition of spectra of the OH stretches of water at hydrophilic and hydrophobic silica surfaces, over the frequency range ~2900 - 3800 cm-1, within 60 s, much shorter than with scanning SFG spectrometers. The ultra-broadband SFG spectrometer reported here can be potentially applied to time-resolved measurements of kinetics at interfaces.

Broadband, rapidly tunable Ti:sapphire-pumped BiB₃O₆ femtosecond optical parametric oscillator

We report a femtosecond optical parametric oscillator (OPO) based on the nonlinear material BiB₃O₆ (BIBO) pumped directly by a Kerr lens mode-locked Ti:sapphire laser. Using a 1.5 mm long BIBO crystal cut at θ=11.4° for collinear type I (e→o+o) phase matching in the xz optical plane, femtosecond signal pulses across 1.4-1.6 μm, and idler pulses across 1.6-1.87 μm spectral range are generated, limited by the reflectivity bandwidth of the OPO mirrors. The high nonlinear gain and large spectral acceptance for type I interaction in the xz plane of BIBO permit rapid and continuous tuning across the entire range by simple fine adjustment of OPO cavity delay or through small changes in the pump wavelength, without varying any other parameters. Additionally, owing to the near-zero group velocity mismatch and dispersion, the OPO supports broad spectrum as wide as 33 nm, which results in self-compressed signal pulses. For 150 fs pump pulses, signal pulses with durations down to 106 fs with a time-bandwidth product of 0.48 are obtained without the need for intracavity dispersion compensation.

Generation of broadly tunable sub-30-fs infrared pulses by four-wave optical parametric amplification

We report on the generation of sub-30-fs near-IR light pulses by means of broadband four-wave parametric amplification in fused silica. This is achieved by frequency downconversion of visible broadband pulses provided by a commercial blue-pumped beta-barium borate crystal-based noncollinear optical parametric amplifier. The proposed method produces the IR idler pulses with energy up to ∼20 μJ and tunable in wavelength from 1 to 1.5 μm. The shortest pulse duration is 17.6 fs, measured at 1.2 μm.

Generation of 8.5-fs pulses at 1.3 microm for ultrabroadband pump-probe spectroscopy

We report on a near-infrared non-collinear optical parametric amplifier (NOPA) based on periodically poled stoichiometric lithium tantalate. The NOPA generates muJ-energy pulses with spectrum spanning the 1-1.7 microm wavelength range, which are compressed to nearly transformlimited 8.5 fs duration by a deformable mirror. By synchronizing this source with a sub-10-fs visible NOPA, we demonstrate an unprecedented combination of temporal resolution and spectral coverage in two-colour pump-probe spectroscopy.

High-energy, sub-30 fs near-IR pulses from a broadband optical parametric amplifier based on collinear interaction in BiB(3)O(6)

We report efficient generation of tunable femtosecond pulses in the near IR using a two stage, white-light seeded, collinear, femtosecond optical parametric amplifier (OPA). The OPA, based on BiB(3)O(6) crystal in both stages and pumped at 807 nm by a 1 kHz Ti:sapphire laser amplifier, provides sub-30 fs signal pulses after compression with energies exceeding 200 microJ, which corresponds to fivefold pulse shortening and approximately 30% internal conversion efficiency in the second stage considering 150 fs pump pulses with 1.5 mJ energy. The corresponding idler pulses with more than 100 microJ have sub-60 fs duration without compression. The first stage alone is capable of producing sub-20 fs pulses near 1400 nm at the microjoule level without using any compression.

Ultrabroadband noncollinear optical parametric amplification with LBO crystal

Ultrabroadband visible noncollinear optical parametric amplification (NOPA) was achieved in an LBO crystal, with a continuum seed pulse generated from a sapphire plate. The spectral bandwidth of the amplified visible pulse was about 200 nm, which can support sub-5 fs pulse amplification. An amplified output of 0.21 microJ with an average gain of about 210 was achieved. This provides, to the best of our knowledge, the first-time demonstration of such broadband amplification with a biaxial nonlinear optical crystal. Both the simulation and experimental results indicate that the LBO has a great potential as nonlinear medium in power amplifier for TW to PW noncollinear optical parametric chirped pulse amplification (NOPCPA) systems.

Sub-two-cycle light pulses at 1.6 microm from an optical parametric amplifier

We generate ultrabroadband pulses, spanning the 1200-2100 nm wavelength range, from an 800 nm pumped optical parametric amplifier (OPA) working at degeneracy. We compress the microjoule-level energy pulses to nearly transform-limited 8.5 fs duration by an adaptive system employing a deformable mirror. To our knowledge, these are the shortest light pulses generated at 1.6 microm.