Generation of carrier-envelope phase-stable two optical-cycle pulses at 2 μm from a noncollinear beta-barium borate optical parametric amplifier

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.

Generation of two successive attosecond pulses in separate spectral domains

We demonstrate that two different single attosecond pulses (SAP) can be obtained from naturally separated spectral domains formed during high-order harmonic generation and propagation in a gas medium. We propose a feasible experimental configuration in which one can obtain an SAP in a lower energy domain (<300 eV), or another SAP in a higher energy domain (>300 eV). Without filtering, a double attosecond pulse emission with fixed temporal separation is obtained. The gap between the two spectral domains is close to the onset of the water window.

Fiber-amplifier-pumped, 1-MHz, 1-µJ, 2.1-µm, femtosecond OPA with chirped-pulse DFG front-end

High-repetition-rate, high-power, few-cycle mid-infrared lasers with carrier-envelope phase (CEP) stabilization are ideal driving sources for studying strong-field nonlinear processes, such as strong-field driven electron emission, solid-state high-harmonic generation, and nonlinear microscopy. Here, we report on a 1-MHz, 1-μJ, femtosecond, 2.1-µm optical parametric amplifier (OPA), pumped by a Yb-doped fiber chirped-pulse amplifier (CPA) and seeded by a chirped-pulse difference-frequency generation (DFG) front-end providing positively chirped 2.1-μm signal pulses. The home-built multi-stage 1030-nm Yb-doped fiber CPA pump laser generates >55-μJ near-transform-limited (245-fs) pulses at 1 MHz repetition rate using a novel 4-pass all-fiber stretcher/front-end for careful dispersion/spectral management. The chirped-pulse DFG scheme is achieved by wave-mixing the 1030 nm pump pulse with a dispersive wave at 645-735 nm generated in a photonic crystal fiber, allowing passive CEP stability of the 2.1-µm pulses. The 2.1-μm pulse is amplified to 1 μJ in a two-stage dispersion-managed optical parametric amplifier (OPA) with a pump energy of ~21 μJ resulting in 95-fs pulses with nice beam profile without additional pulse compression. Multi-μJ, sub-30 fs pulses can be obtained at full pump energy and additional dispersion compensation. The fiber-amplifier-based mid-infrared OPA can be directly applied to high-harmonic generation in solids and optical-field-driven nanophotonic devices and is a compact front-end for a future high-power, high-repetition-rate, long wavelengths CEP-stabilized source for gas-phase high-order harmonic generation.

Millijoule femtosecond pulses at 1937 nm from a diode-pumped ring cavity Tm:YAP regenerative amplifier

We present an infrared source operating at 1937 nm center wavelength capable of generating 1.35 mJ pulse energies with 1 kHz repetition rate and 2 GW peak power based on a diode-pumped Tm:YAP regenerative amplifier. The obtained pulses after 45 round trips have been compressed down to 360 fs. Using only a small portion (15 μJ) of the output of the system we managed to generate a white light continuum in a 3 mm YAG window that exhibits the viability of the system as a suitable candidate for a pumping source of a mid-infrared optical parametric amplifier.

Ultrabroadband microjoule 1.8 μm laser pulse from a single-stage broadband pumped OPA

We propose a broadband pumped optical parametric amplification scheme for the generation of a micojoule few-cycle pulse centered at 1.8 μm. Owing to the opposite chirp of the broadband pump and seed pulses, an idler pulse with an FWHM bandwidth of 434 nm is obtained, which can be effectively compressed to a near-transform-limited duration of 13.1 fs by simply compensating for the linear chirp. The picojoule-level seed is amplified to microjoule level in a single stage with a pump pulse of 100 μJ, corresponding to an overall conversion efficiency of 9%. The presented scheme is potentially applicable in various nonlinear crystals with different kinds of femtosecond laser systems, which provides not only an efficient approach of down-converting a near-infrared laser with moderate energy to the mid-infrared region, but also a suitable seeding source in high-energy OPCPA systems.

Study of middle infrared difference frequency generation using a femtosecond laser source in LGT

We demonstrate phase-matched difference frequency generation in the emerging nonlinear crystal La₃Ga_5.5Ta_0.5O₁₄. Tunable wavelengths between 1.4 and 4.7 μm are generated by using femtosecond sources. We also report on the measurements of the optical damage threshold in the femtosecond regime and on the nonlinear refractive index n₂.

Nondegenerate parametric generation of 2.2-mJ, few-cycle 2.05-μm pulses using a mixed phase matching scheme

We describe the production of 2.2-mJ, ∼6 optical-cycle-long mid-infrared laser pulses with a carrier wavelength of 2.05 μm in a two-stage β-BaB2O4 nondegenerate optical parametric amplifier design with a mixed phase matching scheme, which is pumped by a standard Ti:sapphire chirped-pulse amplification system. It is demonstrated that relatively high pulse energies, short pulse durations, high stability, and excellent beam profiles can be obtained using this simple approach, even without the use of optical parametric chirped-pulse amplification.

Ultrabroadband supercontinuum and third-harmonic generation in bulk solids with two optical-cycle carrier-envelope phase-stable pulses at 2 μm

We report on the generation of ultrabroadband supercontinuum (SC) by filamentation of two optical-cycle, carrier-envelope phase-stable pulses at 2 μm in fused silica, sapphire, CaF₂ and YAG. The SC spectra extend from 450 nm to more than 2500 nm, and their particular shapes depend on dispersive properties of the materials. Prior to spectral super-broadening, we observe third-harmonic generation, which occurs in the condition of large phase and group velocity mismatch and consists of free and driven components. A double-peaked third-harmonic structure coexists with the SC pulse as demonstrated by the numerical simulations and verified experimentally. The SC pulses have stable carrier envelope phase with short-term rms fluctuations of ∼ 300 mrad, as simultaneously measured in YAG crystal by f-2f and f-3f interferometry, where the latter makes use of intrinsic third-harmonic generation.

Efficient, octave-spanning difference-frequency generation using few-cycle pulses in simple collinear geometry

We present experimental observations and corresponding numerical simulations illustrating the difference-frequency generation of mid-infrared radiation using few-cycle near-infrared-to-visible pulses, which yields conversion efficiencies above 12% in beta-barium borate crystal. Type I and type II phase-matching are shown to yield qualitatively different intensity-scaling behavior, with the former showing higher overall efficiency, especially with the addition of a zero-order wave plate for modifying the polarization state of the pulse, and the latter having a better stability of the spectrum versus input intensity.