Noncollinear Optical Parametric Amplifier Research Articles

Generation of 120 GW mid-infrared pulses from a widely tunable noncollinear optical parametric amplifier

We demonstrate a noncollinear optical parametric chirped-pulse amplification scheme for generating high-peak-power tunable mid-infrared (IR) pulses. The high-gain LiNbO(3)-based noncollinear parametric amplifier, seeded by a tunable femtosecond optical parametric amplifier, provides a wide wavelength tuning range from 3.3 to 3.95 μm and a large saturated gain of over 4000 in a single-stage amplifier. The compressed mid-IR pulse has a pulse energy of 13.3 mJ and pulse duration of 111 fs, with a peak power as high as 120 GW. To the best of our knowledge, this is the highest peak power ever reported for 3-5 μm tunable mid-IR lasers.

Effects of nanosecond-scale prepulse on generation of high-energy protons in target normal sheath acceleration

A pulse cleaner based on noncollinear optical-parametric amplification and second-harmonic generation processes is used to improve the contrast of a laser of peak intensity ∼2 × 1019 W/cm2 to ∼1011 at 100 ps before the peak of the main pulse. A 7 MeV proton beam is observed when a 2.5 μm-thick Al foil is irradiated by this high-contrast laser. The maximum proton energy decreases to 2.9 MeV when a low-contrast (∼108) laser is used. Two-dimensional particle-in-cell simulations combined with MULTI simulations show that the maximum proton energy sensitively relies on the detecting direction. The ns-time-scale prepulse can bend a thin target before the main pulse arrives, which reduces maximum proton energy in the target normal sheath acceleration.

Broadband difference frequency mixing between visible and near-infrared pulses for few-cycle pulse generation with stable carrier-envelope phase

Difference frequency generation between broadband visible noncollinear optical parametric amplifier (NOPA) pulses and the fundamental pump laser pulses allows the generation of ultrashort infrared pulses with passively stabilized carrier-envelope phase. A simple prism compressor for the visible NOPA pulses is sufficient to generate few-cycle pulses in the infrared and no additional compression is needed. We theoretically investigate the concept, explain the principles, and demonstrate it for high repetition rate, long pulse durations, and various wavelengths by applying it to a Ti:sapphire and an Yb:KYW-based laser systems. For the latter sub-15 fs phase stable pulses around 1.8 μm with an energy of 100 nJ are obtained at 100 kHz repetition rate.

Direct measurement of the effective input noise power of an optical parametric amplifier

The spontaneous fluorescence background in optical parametric amplifiers is generally attributed to the zero-point fluctuations of the electromagnetic field. These are amplified in parallel to the seed light and lead to an uncompressible superfluorescence background that deteriorates the contrast in optical parametric chirped pulse amplifiers (OPCPA). The absolute level of the underlying parametric fluorescence has not been reported so far. Comparing the fluorescence to low level cw seed light and quantitatively monitoring the output of a noncollinear optical parametric amplifier for both sources, the level is now determined. In a situation of 50 nm visible output bandwidth and low Gaussian spatial modes about 58 photons are found in the signal direction within the femtosecond time window of the amplifier. The superfluorescence level is observed to be proportional to the pump area for constant signal amplification. The implications for the background in high power OPCPA are discussed.

Development of high-energy fiber CPA system

An intense broadband laser system based on a Nd:glass chirped pulse amplifier (CPA) requires a stable front end with good beam quality. To prepare such a front end without using a regenerative amplifier or optical parametric chirped pulse amplification (OPCPA) pumped by the second harmonic of a Nd:YAG laser, we have developed a fiber CPA system using laser diode (LD)-pumped single-mode fibers, large- mode-area (LMA) fibers, and photonic-crystal (rod) fibers. The output pulse energy achieved was 1.2mJ at a central wavelength of 1053nm with a spectral width of 10 nm. The power fluctuation was reduced to 0.4% rms at a repetition rate of 10kHz. The output of this fiber laser is useful as a pump source for a few-cycle noncollinear optical parametric amplifier (NOPA) and a seed for a LD-pumped high-power Nd:glass CPA system.

Tunable High Harmonic Generation driven by a Visible Optical Parametric Amplifier

We studied high-harmonic generation (HHG) in Ar, Ne and He gas jets using a broadly tunable, high-energy optical parametric amplifier (OPA) in the visible wavelength range. We optimized the noncollinear OPA to deliver tunable, femtosecond pulses with 200-500 μJ energy at 1-kHz repetition rate with excellent spatiotemporal properties, suitable for HHG experiments. By tuning the central wavelength of the OPA while keeping energy, duration and beam size constant, we experimentally studied the scaling law of conversion efficiency and cut-off energy with the driver wavelength in argon and helium respectively. Our measurements show a λ−5.9±0.9 wavelength dependence of the conversion efficiency and a λ1.7±0.2 dependence of the HHG cut-off photon energy over the full visible range in agreement with previous experiments of near- and mid-IR wavelengths. By tuning the central wavelength of the driver source and changing the gas, the high order harmonic spectra in the extreme ultraviolet cover the full range of photon energy between ~25 eV and ~100 eV. Due to the high coherence intrinsic in HHG, as well as the broad and continuous tunability in the extreme UV range, a high energy, high repetition rate version of this source might be an ideal seed for free electron lasers.

Beam steering using optical parametric amplification in Kerr medium: a space-time analogy of parametric slow-light

In a way analogous to a light pulse that can be optically delayed via slow light propagation in Kerr-type nonlinear media, we theoretically demonstrate that beam steering and spatial walk-off compensation can be achieved in noncollinear optical parametric amplification. We identify this effect as a result of the quadratic phase shift induced by parametric amplification that leads to the cancellation of the spatial walk-off and collinear propagation of all beams though they have different wavevectors. Experimental evidence is reported of a soliton array steering in a Kerr slab waveguide.

Generation of low-divergence megaelectronvolt ion beams from thin foil irradiated with an ultrahigh-contrast laser

Megaelectronvolt (MeV) ion beams with low divergence (10°) are experimentally generated from a thin foil irradiated by an ultrahigh-contrast laser at a peak intensity of ∼1018 W/cm2. The high-contrast (∼1011) laser is obtained with a pulse cleaner based on noncollinear optical-parametric amplification and second-harmonic generation processes. The effects of the foil density, foil thickness, as well as the density gradients at the front and back sides of the foil are investigated with two-dimensional particle-in-cell simulations. The beam parameters of maximum energy and divergence strongly depend on the density gradients at the back side of the foil.

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

We report on the generation of two optical-cycle, carrier-envelope phase-stable pulses with energy of 15 μJ at central wavelength of 2 μm. Pulses of 15 fs (2.3 optical cycles) duration are obtained by difference-frequency generation, which at the same time provides passive carrier-envelope phase stabilization, and noncollinear optical parametric amplification in beta-barium borate crystal, which is shown to provide broad phase-matching bandwidth if seeded by pulses in the 1.6-2.6 μm wavelength range. Pulse compression is achieved by means of a simple propagation through the optical setup and by precisely controlling the initial chirp of the pulses to be frequency downconverted.

Phase-matching loci and angular acceptance of non-collinear optical parametric amplification

A general study of phase-matching loci and associated angular acceptances is performed in the case of non-collinear parametric amplification. Numerical and analytical calculations, as well as measurements, are described for the uniaxial BBO crystal and the biaxial LBO crystal.

Real-time observation of vibrational quantum beat in condensed phase by 20 fs time-resolved spectroscopy

Impulsive coherent vibrational spectroscopy is a kind of time-resolved spectroscopy methodology with a pulse duration of the femtosecond laser shorter than the molecular vibrational period. Usually, it is based on pump-probe technique and is utilized to real-time observation of the molecular vibrational dynamics coupled to the electronic ground or excited state. We have built an impulsive coherent vibrational spectroscopy setup based on a sub-20 fs, 550 to 700 nm tunable non-collinear optical parametric amplifier and performed pump-probe experiment with an Oxazine 720 methanol solution as the sample. Two vibrational quantum beats with frequency of 592 and 678 cm-1 were observed and the corresponding vibrational periods are 56.3 and 49.2 fs respectively.

Generation of 30 fs pulses tunable from 189 to 240 nm with an all-solid-state setup

Fully tunable deep UV pulses of 30 fs duration are generated in an all-solid-state scheme from 200 fs long pump pulses of a Ti:sapphire amplifier. The tunability comes from a noncollinear optical parametric amplifier with tailored spectral width. The output pulses are frequency-doubled in a 50 μm BBO crystal and subsequently mixed in a 32 μm BBO crystal with part of the Ti:sapphire output. The compression is solely performed in the visible. This makes the setup extremely simple and efficient. Less than 400 μJ pump energy suffice to obtain submicrojoule deep UV pulses. The strategy for the bandwidth and chirp management is explained in detail.

Control of nonlinear spectral phase induced by ultra-broadband optical parametric amplification

Optical parametric amplifiers (OPAs) impose an optical parametric phase (OPP) onto the amplified signal. It manifests itself as a spectral phase in the case of broadband signals and, therefore, hampers pulse compression. Here we present, for the first time, a complete experimental characterization of this OPP for different ultra-broadband noncollinear OPA configurations. This measurement allows us to compensate the OPP and to achieve Fourier-limited pulses as short as 1.9 optical cycles. A numerical model is in excellent agreement with our measurements and reveals the importance of high order phase compensation in the case of noncollinear phase matching. In contrast, operation at degeneracy enables almost complete compensation of the OPP by second-order dispersion only.

Temporal and spectral characterizations of tunable noncollinear optical parametric amplifier

We experimentally investigate the temporal and spectral information from a broadband tunable femtosecond noncollinear optical parametric amplifier (NOPA), and present the spectral characterizations through the time–bandwidth products (τΔv). The time–bandwidth products of the signal are from 0.26 to 0.36, which are very similar to that of the pump (about 0.34) due to the time-correlated radiation. However, the time–bandwidth products of the idler are from 0.13 to 0.63, which present a larger variable range due to the more spatial freedom. We also experimentally demonstrate that the spectral bandwidth of the output signal is gradually widened when it is tuned to the longer central wavelength, which is approximatively following a λ2 scaling law.

Cut-off scaling of high-harmonic generation driven by a femtosecond visible optical parametric amplifier

We studied high-harmonic generation (HHG) in Ar, Ne and He gas jets using a broadly tunable, high-energy optical parametric amplifier (OPA) in the visible wavelength range. We optimized the noncollinear OPA to deliver tunable, femtosecond pulses with 200–500 µJ energy at the 1 kHz repetition rate with excellent spatiotemporal properties, suitable for HHG experiments. By tuning the central wavelength of the OPA while keeping other parameters (energy, duration and beam size) constant, we experimentally studied the scaling law of cut-off energy with the driver wavelength in helium. Our measurements show a λ1.7 + 0.2 dependence of the HHG cut-off photon energy over the full visible range in agreement with previous experiments of near- and mid-IR wavelengths. By tuning the central wavelength of the driver source, the high-order harmonic spectra in the extreme ultraviolet cover the full range of photon energy between ∼25 and ∼100 eV. Due to the high coherence intrinsic in HHG, as well as the broad and continuous tunability in the extreme UV range, a high energy, high repetition rate version of this source might be an ideal seed for free electron lasers.

Sub-10-fs deep-ultraviolet light source with stable power and spectrum

In some applications of ultrafast spectroscopy that employ sub-10-fs pulses, the pulse spectrum and power need to be stable for several tens of minutes. In this study, we generate sub-10-fs deep-ultraviolet (DUV) pulses with such stabilities by chirped-pulse four-wave mixing. A power fluctuation of less than 3% rms was realized by employing stabilization schemes that employ a power stabilizer. The pulses generated in this study have been applied to transient absorption spectroscopy in the DUV with a sub-10-fs time resolution [Phys. Chem. Chem. Phys.14, 6200 (2012).10.1039/c2cp23649d]. This sub-10-fs DUV source has a similar performance to widely used noncollinear optical parametric amplifiers.

Broadband noncollinear optical parametric amplification without angularly dispersed idler

We report a new scheme for direct generation of broadband angular-dispersion-free mid-IR idler pulses via noncollinear optical parametric amplification when group-velocity matched wavelengths cannot be found and the traditional noncollinear geometry fails to increase the phase-matching bandwidth. The scheme does not require any post-amplification idler angular dispersion compensation. We derive and interpret the condition for broadband amplification and absence of idler angular dispersion. A broadband angular-dispersion-free 2.15 μm idler pulse is generated as an experimental demonstration. We identify the potential of the scheme to generate a broadband 3.5 μm idler, with a bandwidth supporting a sub-two-cycle pulse.

Design Considerations for Dispersion Control with a Compact Bonded Grism Stretcher for Broadband Pulse Amplification

We report on the design of a compact grism-pair stretcher for a near-infrared noncollinear optical parametric chirped-pulse amplification (OPCPA) system. The grisms are produced by bonding a grating to a prism using a resin. The stretcher is capable of controlling a bandwidth of over 300 nm, which is suitable for parametric amplification of few-cycle pulses. After amplification, pulses can be compressed by the dispersion of optical glass, and the residual group-delay can be compensated with an acousto-optic programmable dispersive filter (AOPDF).

Generation of tunable few optical-cycle pulses by visible-to-infrared frequency conversion

We demonstrate a simple method for infrared few optical-cycle pulse generation, which is based on collinear visible-to-infrared frequency conversion and involves difference-frequency generation and subsequent two-step optical parametric amplification. The numerical simulations and experiments using BBO crystals show an efficient frequency down conversion of visible ∼20 fs pulses from a commercial blue-pumped noncollinear optical parametric amplifier yielding 1.2–2.4 μm tunable sub-100 μJ pulses with duration of 3 to 5 optical-cycles. The proposed method could be readily extended to generate few optical-cycle pulses in the mid-infrared spectral range (up to 5.5 μm) using, e.g., LiIO3 and LiNbO3 crystals, as demonstrated by the numerical simulations. In these crystals, even shorter, two-optical-cycle mid-infrared pulses could be obtained at particular wavelengths where group velocity matching between the signal and idler waves is achieved.

Ultrabroadband femtosecond two-dimensional ultraviolet transient absorption

We present a broadband two-dimensional transient absorption setup for the UV around 300 nm with a time resolution of 150 fs. A narrowband, frequency tunable pump pulse and a broadband probe pulse are generated from the output of a noncollinear optical parametric amplifier operated at 20 kHz repetition rate and combined in a spectrally resolved transient absorption experiment. The high repetition rate and low noise of the setup allow us to acquire high quality two-dimensional data as a function of time delay with an unsurpassed frequency window of 10,000 and 8000 cm(-1) along the probe and pump axis, respectively. The performance of the setup is demonstrated on 2,5-Diphenyloxazol dissolved in cyclohexane.