Broadband Optical Parametric Amplification Research Articles

Efficient single-cycle mid-infrared femtosecond laser pulse generation by spectrally temporally cascaded optical parametric amplification with pump energy recycling.

We proposed spectrally temporally cascaded optical parametric amplification (STOPA) using pump energy recycling to simultaneously increase spectral bandwidth and conversion efficiency in optical parametric amplification (OPA). Using BiB3O6 and KTiOAsO4 nonlinear crystals, near-single-cycle mid-infrared (MIR) pulses with maximum energy conversion efficiencies exceeding 25% were obtained in simulations. We successfully demonstrated sub-two-cycle, CEP-stable pulse generation at 1.8 µm using a four-step STOPA system in the experiment. This method provides a solution to solve the limitations of the gain bandwidth of nonlinear crystals and the low conversion efficiency in broadband OPA systems, which is helpful for intense attosecond pulse generation and strong laser field physics studies.

Characteristics of broadband OPCPA based on DKDP crystals with different deuterations for the SEL-100 PW laser system.

We present the performances of a broadband optical parametric chirped pulse amplification (OPCPA) using partially deuterated potassium dihydrogen phosphate (DKDP) crystals with deuteration levels of 70% and 98%. When pumped by a Nd:glass double frequency laser, the OPCPA system using the 98% deuterated DKDP crystal achieves a broad bandwidth of 189 nm (full width at 1/e2 maximum) from 836 nm to 1025 nm. For the DKDP crystal with length of 43 mm, the pump-to-signal conversion efficiency reaches 28.4% and the compressed pulse duration is 13.7 fs. For a 70% deuterated DKDP crystal with a length of 30 mm, the amplified spectrum ranges from 846-1021 nm, the compressed pulse duration is 15.7 fs, and the conversion efficiency is 25.5%. These results demonstrate the potential of DKDP crystals with higher deuteration as promising nonlinear crystals for use as final amplifiers in 100 Petawatt (PW) laser systems, supporting compression pulse duration shorter than 15 fs.

Serial synthesis of mid-infrared optical parametric amplifiers for enlarging a gain bandwidth.

Broadband optical parametric amplifiers (OPAs) require a group-velocity matching between the signal and the idler. For mid-infrared OPAs, however, the group-velocity matching is usually difficult to meet, rendering a limited gain bandwidth. Here, we report a serial synthesis of bandwidth-limited OPAs to provide a broad gain bandwidth. In a proof-of-principle experiment, two mid-IR OPAs based on KTA crystals with different phase-matching angles are sequentially employed to amplify different spectral regions of a broad seed pulse centered at 3.1 µm. Compared to the traditional two-stage OPA, here the gain bandwidth is nearly doubled, resulting in a much shorter compressed pulse. Such a serial synthesis approach, independent of a nonlinear crystal and an interaction wavelength, particularly suits for enlarging the gain bandwidth of OPAs when broadband amplification is impossible to achieve by a single crystal.

Ultra-broad-spectrum laser-pulse damage of low-dispersion mirrors

The broadband optical parametric chirped-pulse amplification scheme is considered as a promising approach for developing the 100 PW or even exawatt laser facilities. Based on a quarter-wavelength optical-thickness mirror with a reverse-chirped structure, a Nb2O5/SiO2 low-dispersion mirror (LDM) and a Nb2O5–Al2O3/SiO2 composite LDM (CLDM) for a 910 (±100 nm) laser system are designed and experimentally evaluated. The laser damage properties of the mirrors were investigated in an uncompressed nanosecond laser pulse with a spectrum bandwidth of 200 nm for the first time. From the aspects of both broad-spectrum electric field and thermal stress, the damage behavior is elucidated. The results show that the protective layer has both positive and negative effects in the broad spectrum and the competing results of the two effects determine whether the protective layer can play a protective role. Damage morphology and thermal stress calculations show that the laser introduced thermal stress mismatch will lead to the peeling damage of CLDM. This study shows that broad-spectrum optics should be designed and fabricated by considering the electric field of all spectrum components and thermodynamic properties of layer materials; this provides insight into the development of high-performance broad-spectrum optics.

Ultrabroadband OPA in YCOB with a sub-ps Pump Source

We demonstrate the broadband optical parametric amplification of near-infrared laser pulses using a single yttrium calcium oxyborate (YCOB) crystal pumped in a noncollinear geometry by a sub-picosecond, milijoule-level source. The crystal uses an optimized orientation for phase matching outside of the principal planes, enabling ultrabroadband amplification (gain of ∼800) in the range of 750–950 nm and supporting down to 7 fs pulses.

Effect of the pump beam profile and wavefront on the amplified signal wavefront in optical parametric amplifiers.

We present a theoretical and experimental analysis of the signal phase introduced by the pump-beam wavefront and spatial profile during optical parametric amplification (OPA) process. The theory predicts the appearance of an additional wavefront in the amplified signal beam that is proportional to the spatial derivative of the pump-beam wavefront. The effect of the pump-beam profile on the signal-beam wavefront is also investigated. Our experiments tested these theoretical predictions by comparing the wavefront of the signal beam before and after amplification in a multi-joule broadband OPA. The measured signal wavefront was shown to have the expected dependence on the pump-beam profile and wavefront. These results can be considered when designing petawatt-scale ultrabroadband optical parametric chirped-pulse-amplification systems.

Broadband optical parametric amplification using PPLN waveguide pumped by detuned second harmonic.

Optical parametric amplification in the range of 1.3-1.8 µm was demonstrated by using a periodically poled LiNbO3 (PPLN) waveguide as a nonlinear medium by varying the detuning of the pump wavelength. A wide range of detuning was enabled by using a multiple-quasi-phase-matched (M-QPM) LiNbO3 waveguide for pump generation through second harmonic generation (SHG) and temperature control of the PPLN waveguide. Broadband optical amplification and wavelength conversion through difference frequency generation (DFG) are considered useful for widening the bandwidth of optical communication.

Multi-pass cells for post-compression of ultrashort laser pulses

Ultrafast lasers reaching extremely high powers within short fractions of time enable a plethora of applications. They grant advanced material processing capabilities, are effective drivers for secondary photon and particle sources, and reveal extreme light-matter interactions. They also supply platforms for compact accelerator technologies, with great application prospects for tumor therapy or medical diagnostics. Many of these scientific cases benefit from sources with higher average and peak powers. Following mode-locked dye and titanium-doped sapphire lasers, broadband optical parametric amplifiers have emerged as high peak- and average power ultrashort pulse lasers. A much more power-efficient alternative is provided by direct post-compression of high-power diode-pumped ytterbium lasers—a route that advanced to another level with the invention of a novel spectral broadening approach, the multi-pass cell technique. The method has enabled benchmark results yielding sub-50-fs pules at average powers exceeding 1 kW, has facilitated femtosecond post-compression at pulse energies above 100 mJ with large compression ratios, and supports picosecond to few-cycle pulses with compact setups. The striking progress of the technique in the past five years puts light sources with tens to hundreds of TW peak and multiple kW of average power in sight—an entirely new parameter regime for ultrafast lasers. In this review, we introduce the underlying concepts and give brief guidelines for multi-pass cell design and implementation. We then present an overview of the achieved performances with both bulk and gas-filled multi-pass cells. Moreover, we discuss prospective advances enabled by this method, in particular including opportunities for applications demanding ultrahigh peak-power, high repetition rate lasers such as plasma accelerators and laser-driven extreme ultraviolet sources.

Lineshape characterization of excitons in monolayer WS2 by two-dimensional electronic spectroscopy.

The optical properties of monolayer transition metal dichalcogenides (TMDCs), an important family of two-dimensional (2D) semiconductors for optoelectronic applications, are dominated by two excitons A (XA) and B (XB) located at K/K's valleys. The lineshape of the excitons is an indicator of the interaction of the excitons with other particles and also largely determines the performance of TMDC-based optoelectronic devices. In this work, we apply 2D electronic spectroscopy (2DES), which enables separation of the intrinsic homogeneous linewidth and the extrinsic inhomogeneous linewidth, to dissect the lineshape of XA in monolayer WS2. With a home-built broadband optical parametric amplifier, the 2D spectra give the exciton linewidth values for extensive ranges of excitation densities and temperatures, reflecting inter-exciton and exciton–phonon interactions. Meanwhile, the time-domain evolution of the lineshape reveals a similar rate of spectral diffusion to that in quantum wells (QWs) based on III–V semiconductors.

Temperature-insensitive broadband optical parametric chirped pulse amplification based on a tilted noncollinear QPM design.

Ultrafast pulsed laser of high intensity and high repetition rate is the combined requisite for advancing strong-field physics experiments and calls for the development of thermal-stable ultrafast laser systems. Noncollinear phasing matching (PM) is an effective solution of optimizing the properties of optical parametric chirped pulse amplification (OPCPA) to achieve broadband amplification or to be temperature-insensitive. But as a cost, distinct noncollinear geometries have to be respectively satisfied. In this paper, a noncollinear quasi-phase-matching (QPM) scheme of both temperature- and wavelength-insensitive is presented. With the assistance of the design freedom of grating wave vector, the independent noncollinear-angle requirements can be simultaneously realized in a tilted QPM crystal, and the temperature-insensitive broadband amplification is achieved. Full-dimensional spatial-temporal simulations for a typical 1064 nm pumped mid-IR OPCPA at 3.4 µm are presented in detail. Compared with a mono-functional temperature-insensitive or broadband QPM scheme, the presented QPM configuration shows a common characteristic that simultaneously optimizes the thermal stability and the gain spectrum. Broadband parametric amplification of a ∼40 fs (FWHM) pulsed laser is achieved with no signs of gain-narrowing. Both of the beam profiles and the amplified spectra stay constant while the temperature is elevated by ∼100°C. Finally, influence of the QPM grating errors on the gain spectrum is discussed.

Net optical parametric gain in a submicron silicon core fiber pumped in the telecom band

A silicon core fiber (SCF) has been designed and fabricated with a dispersion engineered profile to support broadband optical parametric amplification across the telecom window. The combination of low optical transmission losses and high coupling efficiency of the SCF platform has allowed for an on-off optical parametric gain up to 9 dB, without experiencing gain saturation due to nonlinear absorption, resulting in a net off-waveguide gain of ∼2 dB. The ability to splice the SCFs with conventional silica fiber systems opens a route to compact and robust all-fiber integrated optical parametric amplifiers and oscillators that could find use in telecoms systems.

High Energy, Sub-Cycle, Field Synthesizers

Tailoring the electromagnetic field transients has been a prominent research focus over the last decade. Advances in ultrashort pulse generation and stabilizing the carrier phase of the electromagnetic field relative to its envelope allowed for extension of coherent synthesis to optical frequencies and ultrashort pulse domain at tens of microjoules of energy. In parallel, ytterbium-doped lasers become a mature technology. They are able to deliver down to 1-picosecond scale pulses at hundreds of millijoule energy and kilowatt-scale average power, making them suitable frontends for scaling the energy and power of light transients. In this paper, we discuss two conceptual schemes, our experimental results, and technological challenges for generation of sub-cycle light transients based on Yb:YAG thin-disk lasers by direct and efficient spectral broadening of ytterbium-doped lasers, and by coherent combination of pulses from multiple broadband optical parametric amplifiers. Moreover, a conceptual design study for a novel synthesis scheme based on polarization splitting of a broadband spectrum and amplification of each polarization in a separate stage is presented. The novel sources hold promise for studying and controlling the nonlinear interactions of matter with custom-tailored light transients at a sub-cycle period of their electric field, opening up unprecedented opportunities in attoscience and strong-field physics.

Scanning broadband optical parametric chirped pulse amplification based on optical beam deflection

One of the goals pursued in laser pulse is to achieve a laser with a shorter duration and higher intensity. In the past two decades, the laser pulse duration has been shortened by more than 7 orders of magnitude due to the development of Q-switched, Mode-locked and pulse compression technology. The peak power of laser pulse has been increased to PW, even EW and ZW from initial MW with the development of pulse amplification technology, whose focused intensity can reach to 10<sup>23</sup> W/cm<sup>2</sup>. Thus, it provides unprecedented extreme conditions, and speeds up the laser applications in ultrafast nonlinear optics, strong field physics, fast ignition of laser nuclear fusion, optic communication, etc. The optical parametric chirped pulse amplification (OPCPA) is one of the important technologies in ultra-short laser pulse field. It is of great significance to increase the gain bandwidth for improving the conversion efficiency of OPCPA and achieving broadband optical parametric amplification. Combining the optical beam deflection and non-collinear OPCPA, a novel scanning broadband OPCPA model is proposed based on the optical beam deflection. The basic principle of increasing the gain bandwidth for the scanning broadband OPCPA is analyzed theoretically, which ensures the phase matching of each frequency component of signal by optical beam deflecting to change the non-collinear angle constantly. Namely, the non-collinear angles of incident frequency components of signal are different from each other, which, however, makes the whole phase matching of signal, i.e. momentum conservation in optics. The optical parametric amplification of signal pulse with 800 nm central wavelength and almost 100 nm bandwidth is simulated numerically by the proposed scanning broadband OPCPA. The results show that the bandwidth after being amplified is almost the same as before and there is no spectral narrowing, and the scanning broadband OPCPA increases the gain bandwidth and conversion efficiency greatly compared with the amplification with a constant given non-collinear angle, which leads to broadband optical parametric amplification. Finally, it is necessary to make sure that the on-load voltage to the KTN crystal matches with the frequency of signal pulse in time and reduces the unfavorable voltage deviation and time-delay for the maximizing gain bandwidth and conversion efficiency and ensuring the phase matching of each signal frequency component. The results of this paper not only provide an approach to increasing the gain bandwidth of OPCPA, but also supply some theoretical references and the basis for the experimental work of OPCPA in ultra-short laser pulse system.

Time-resolved photoemission electron microscopy of a plasmonic slit resonator using 1 MHz, 25 fs, UV-to-NIR-tunable pulses

We discriminate different field dynamics across distances as small as 33 nm within a plasmonic slit resonator using aberration-corrected photoemission electron microscopy and a tunable broadband optical parametric amplifier at 1 MHz repetition rate.

An Octave-Spanning Optical Parametric Amplifier Based on a Low-Dispersion Silicon-Rich Nitride Waveguide

Optical amplification is one of the main applications of nonlinear optics, and broadband optical parametric amplifiers are useful not only for multiple data channels in a communication system but for ultrashort optical pulses in ultrafast optics as well. We propose an octave-spanning parametric amplifier in a dual-pump scheme, enabled by advanced dispersion flattening and strong Kerr nonlinearity in a silicon-rich nitride waveguide. A comprehensive nonlinear model is used to study cascaded (non)degenerate parametric processes, by taking wavelength-dependent nonlinearity and all-order dispersion into account. The obtained gain spectrum has a 3-dB bandwidth of one octave from 126 to 244 THz (i.e., 1151 nm), and the gain reaches 11 dB. We show that the proposed amplifier is in principle tolerant to variations of physical parameters, such as pump power, propagation loss, and dispersion. We also examine the amplification of an ultrafast 13-fs soliton pulse with a sech2 waveform. The gain can reach 8 dB, with the pulse shape well maintained.

Spectral pulse shaping of a 5 Hz, multi-joule, broadband optical parametric chirped pulse amplification frontend for a 10 PW laser system.

We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4J pulses at a repetition rate of 5Hz. It will serve as a frontend for the 1.5kJ, <150 fs, 10PW laser beamline currently under development by a consortium of National Energetics and Ekspla. The spectrum of the OPCPA system is precisely controlled by arbitrarily generated waveforms of the pump lasers. To fully exploit the high flexibility of the frontend, we have developed a 1D model of the system and an optimization algorithm that predicts suitable pump waveform settings for a desired output spectrum. The OPCPA system is shown to have high efficiency, a high-quality top-hat beam profile, and an output spectrum demonstrated to be shaped consistently with the theoretical model.

Decoupling phase-matching bandwidth and interaction geometry using non-collinear quasi-phase-matching gratings.

In optical parametric amplification (OPA) of broadband pulses, a non-collinear angle between the interacting waves is typically introduced in order to achieve broadband phase-matching. Consequently, bandwidth and beam geometry are closely linked. This coupling restricts the geometrical layout of an OPA system. Here, we demonstrate a quasi-phase-matching (QPM) geometry for broadband OPA in which a transverse component is introduced to the QPM grating to impose an additional momentum on the generated wave. This momentum shift detunes the wavelength where the signal and the idler are group-velocity matched, thereby allowing for broadband phase-matching without having to add a non-collinear angle between the interacting waves. We present two experimental configurations making use of this principle, and propose a third configuration with the potential to further simplify ultra-broadband OPA system architectures.

2.5 TW, two-cycle IR laser pulses via frequency domain optical parametric amplification.

Broadband optical parametric amplification in the IR region has reached a new milestone through the use of a non-collinear Frequency domain Optical Parametric Amplification system. We report a laser source delivering 11.6 fs pulses with 30 mJ of energy at a central wavelength of 1.8 μm at 10 Hz repetition rate corresponding to a peak power of 2.5 TW. The peak power scaling is accompanied by a pulse shortening of about 20% upon amplification due to the spectral reshaping with higher gain in the spectral wings. This source paves the way for high flux soft X-ray pulses and IR-driven laser wakefield acceleration.

Broadband optical parametric chirped pulse amplification in K3B6O10Br crystal near 800 nm

Broadband optical parametric chirped pulse amplification (OPCPA) of the K3B6O10Br (KBOB) crystal at a central wavelength of 800 nm has been demonstrated for the first time. Using type-1 non-collinear phase matching, a 52 nm FWHM bandwidth was achieved around 800 nm. The 0.25 mJ signal was amplified to 23.92 mJ at the pump intensity of 2.1 GW cm−2. The energy gain was 95.68. After compression, 15.31 mJ to 31.9 fs pulses were obtained. The results confirm that KBOB crystal is a potential alternative for efficient, broadband OPCPA near 800 nm.

Versatile backconversion-inhibited broadband optical parametric amplification based on an idler-separated QPM configuration.

Conversion efficiency and phase-matching (PM) bandwidth are both critical issues for broadband parametric processes. In some sense, they determine the highest peak power achieved via the optical parametric amplification. In this Letter, a versatile idler-separated quasi-phase matching scheme capable of both backconversion circumvention and ultra-broadband PM is presented. Full-dimensional spatial-temporal simulations for the typical optical parametric chirped pulse amplification processes at 800nm and 3.4μm were presented in detail. By virtue of the broad PM bandwidth on account of the non-collinear PM configuration, the backconversion circumvention on account of the idler-separated design, and the walk-off self-compensation on account of the symmetrical tilting grating patterns, significantly improved gain bandwidth, extremely high conversion efficiency, and a well-preserved beam profile are simultaneously achieved. Compared with the collinear configuration, the peak power can be potentially enhanced by 5-10 times under the same operation circumstances.