Optical Parametric Chirped Pulse Amplification Research Articles

A Review of Optical Parametric Amplification at the Vulcan Laser Facility

An overview of Optical Parametric Chirped Pulse Amplification (OPCPA) is given as the basis for the next generation of ultra-intense laser systems (>1×1023 W/cm2). The benefits and drawbacks of OPCPA are discussed to explain the choice behind the decisions for the direction of the Central Laser Facility’s (CLF) upcoming Vulcan 20-20 project. A history of OPCPA use at the CLF is described to surmise the foundation of the confidence in this technology for Vulcan 20-20; a 20 PW user facility for high-intensity plasma physics.

Efficient noncollinear optical parametric chirped-pulse amplification in oversaturation region

Optical parametric chirped pulse amplification (OPCPA) is the workhorse to generate intense ultrashort pulses across a broad wavelength range. Typically, OPCPA operates in the saturation region, but barely in the oversaturation region due to efficiency drop caused by back conversion. Through numerical simulations, we reveal the potential of noncollinear OPCPA to achieve significantly higher conversion efficiency in the oversaturation regime compared to the recognized saturation efficiency. This enhancement stems from the suppression of back conversion facilitated by noncollinearity-induced idler dissipation. Besides offering high efficiency and robustness, the oversaturated noncollinear OPCPA also exhibits acceptable spatial and temporal properties, as well as spatiotemporal coupling properties. These findings hold promise for enhancing the final stage of a noncollinear OPCPA system, where a high conversion efficiency is essential.

Crystal growth, structure, spectral and thermal properties of ScxY1-xCOB single crystals

Yttrium calcium oxyborate (YCOB) crystals are excellent nonlinear optical crystals. To enhance the thermal properties of YCOB crystal, Sc-doped YCOB crystals, denoted as ScxY1-xCa4O(BO3)3 (x = 0.1 and 0.2) were grown using the Czochralski method along the b-direction. Various measurements, including X-ray powder diffraction, rocking curve analysis, inductively coupled plasma-optical emission spectroscopy (ICP-OES), transmission spectroscopy, density measurements, and thermal property assessments, were conducted to evaluate the characteristics of the ScxY1-xCOB crystals. The results indicated that ScxY1-xCOB crystals have an isostructural arrangement like YCOB, with segregation coefficients of approximately 0.2. The full width at half maximum (FWHM) values of the rocking curves of the ScxY1-xCOB (x = 0.1 and 0.2) crystals are 33.9″ and 29.3″, respectively. Furthermore, the specific heat, thermal diffusion coefficients and thermal conductivity of the ScxY1-xCOB crystals were examined in the temperature range of 298–573 K, which were found to be higher than those of pure YCOB. These high-quality ScxY1-xCOB crystals are expected to serve as suitable nonlinear optical crystals media for optical parametric chirped pulse amplification (OPCPA) applications.

Toward high-energy few-cycle optical vortices with minimized topological charge dispersion.

A simple approach to generate high-energy few-cycle optical vortices with minimized topological charge dispersion is introduced. By means of numerical simulations, it is shown that, by leveraging the intrinsic properties of optical parametric chirped pulse amplification (OPCPA), clean transfer of topological charge from a high-energy narrowband pump pulse to a broadband idler is feasible under certain particular conditions, enabling the generation of high-energy few-cycle vortex pulses with extremely low topological charge dispersion.

Ultrarelativistic electron beams accelerated by terawatt scalable kHz laser

We show the laser-driven acceleration of unprecedented, collimated (2 mrad divergence), and quasi-monoenergetic (25% energy spread) electron beams with energy up to 50 MeV at 1 kHz repetition rate. The laser driver is a multi-cycle (15 fs) 1 kHz optical parametric chirped pulse amplification system, operating at 26 mJ (1.7 TW). The scalability of the driver laser technology and the electron beams reported in this work pave the way toward developing high-brilliance x-ray sources for medical imaging and innovative devices for brain cancer treatment and represent a step toward the realization of a kHz GeV electron beamline.

Experimental demonstration on 400 nm-scale bandwidth optical parametric chirped-pulse amplification based on mixed cascaded crystals.

We present an optical parametric chirped-pulse amplification (OPCPA) based on mixed cascaded crystals, taking advantage of the unique parametric phase-matching of lithium triborate (LiB3O5, LBO) and yttrium calcium oxyborate ((YCa4O(BO3)3, YCOB) crystals. The OPCPA properties of LBO at 880 nm and YCOB at 750 nm are studied respectively. After amplification by two LBO and two YCOB crystals, a total signal gain of 108 and spectral bandwidth close to 400 nm is obtained. After accurate dispersion compensation with a grating-pair compressor and chirped mirror compensator, a pulse duration of 9.4 fs is obtained by a SHG-frequency-resolved optical grating (FROG). This approach will be of great significance in high energy amplifier for high peak power few-cycle laser sources.

Compact, ultrastable, high repetition-rate 2 μm and 3 μm fiber laser for seeding mid-IR OPCPA.

We report a compact and reliable ultrafast fiber laser system optimized for seeding a high energy, 2 μm pumped, 3 μm wavelength optical parametric chirped pulse amplification to drive soft X-ray high harmonics. The system delivers 100 MHz narrowband 2 μm pulses with >1 nJ energy, synchronized with ultra-broadband optical pulses with a ∼1 μm FWHM spectrum centered at 3 μm with 39 pJ pulse energy. The 2 μm and 3 μm pulses are derived from a single 1.5 μm fiber oscillator, fully fiber integrated with free-space downconversion for the 3 μm. The system operates hands-off with power instabilities <0.2% over extended periods of time.

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.

Bright continuously tunable vacuum ultraviolet source for ultrafast spectroscopy

Ultrafast electron dynamics drive phenomena such as photochemical reactions, catalysis, and light harvesting. To capture such dynamics in real-time, femtosecond to attosecond light sources are extensively used. However, an exact match between the excitation photon energy and a characteristic resonance is crucial. High-harmonic generation sources are advantageous in terms of pulse duration but limited in spectral tunability in the vacuum ultraviolet range. Here, we present a monochromatic femtosecond source continuously tunable around 21 eV photon energy utilizing the second harmonic of an optical parametric chirped pulse amplification laser system to drive high-harmonic generation. The unique tunability of the source is verified in an experiment probing the interatomic Coulombic decay in doped He nanodroplets across the He absorption bands. Moreover, we achieved intensities sufficient for driving collective processes in multiply excited helium nanodroplets, which have been previously observed only at free electron lasers.

Efficient and high-spatiotemporal-quality terawatt-class mid-infrared optical parametric amplifiers by spatially shaped pumping

We propose a method to efficiently generate terawatt (TW)-class mid-infrared (MIR) femtosecond laser pulses with high spatiotemporal quality through optical parametric chirped-pulse amplification (OPCPA). By transforming the pump-beam profile for the OPCPA from Gaussian to flat-top using a designed field mapping optics consisting of two aspherical lenses, we obtain a TW-class femtosecond laser pulse at 2 µm with a conversion efficiency of over 36% according to our simulations. Furthermore, the spatiotemporal coupling effects are greatly suppressed in our method compared to an OPCPA system that is pumped by a widely employed Gaussian profile beam. Our work provides a simple and robust method for developing OPCPA systems with high efficiency and high pulse quality.

Nonlinear compression of few-cycle multi-mJ 5 µm pulses in ZnSe around zero-dispersion.

We present a compact nonlinear compression scheme for the generation of millijoule few-cycle pulses beyond 4 µm wavelength. For this purpose 95 fs pulses at 5 µm from a 1 kHz midwave-IR optical parametric chirped pulse amplifier (OPCPA) are spectrally broadened due to a self-phase modulation in ZnSe. The subsequent compression in a bulk material yields 53 fs pulses with 1.9 mJ energy. The compression succeeds efficiently with only slight beam distortions and an energy throughput of 85%, which results in a peak power of 34 GW. The nonlinear refractive index of ZnSe was derived from the nonlinear compression and self-focusing measurements. Furthermore, we explore to which extent multiphoton absorption affects the nonlinear compression regime.

Research on the pre-pulses caused by post-pulses in the optical parametric chirped-pulse amplifier.

Pre-pulses caused by the post-pulses in the optical parametric chirped-pulse amplifier were comprehensively studied for the first time, including the underlying mechanism for the delay-shift of pre-pulses, the intensity variation of pre-pulses affected by the initial delay of post-pulses and the pump energy, and also the nonlinear beat noise. The simulation and measurement confirmed that the high-order dispersion of the pulse stretcher was the main cause for the delay-shift of pre-pulses, which should be similar with the chirped-pulse amplifiers. The intensity of pre-pulses would decrease significantly as the initial delay of post-pulses increased, but would increase with the growth of pump energy. Moreover, the temporal position of the nonlinear beat noise in the experiment was successfully predicted by our simulation. This work could help us better understand the pre-pulses in OPCPA and provide helpful guidance for designing high-contrast laser systems.

A versatile high-average-power ultrafast infrared driver tailored for high-harmonic generation and vibrational spectroscopy.

We report on an ultrafast infrared optical parametric chirped-pulse amplifier (OPCPA), pumped by a 200-W thin-disk Yb-based regenerative amplifier at a repetition rate of 100 kHz. The OPCPA is tunable in the spectral range 1.4-3.9 [Formula: see text]m, generating up to 23 W of < 100-fs signal and 13 W of < 200-fs idler pulses for infrared spectroscopy, with additional spectral filtering capabilities for Raman spectroscopy. The OPCPA can also yield 19 W of 49-fs 1.75-[Formula: see text]m signal or 5 W of 62-fs 2.8-[Formula: see text]m idler pulses with active carrier-to-envelope-phase (CEP) stabilisation for high-harmonic generation (HHG). We illustrate the versatility of the laser design, catering to various experimental requirements for probing ultrafast science.

Evolutionary optimization and long-term stabilization of a white-light seeded two-stage OPCPA seed laser.

Ultrafast laser systems, such as optical parametric chirped pulse amplifiers (OPCPA), are complex tools. Optimizing laser performance for a given application is often plagued by intricate couplings between different output parameters, making simultaneous control of multiple pulse properties difficult. Here, we experimentally demonstrate an autonomous tuning procedure of a white-light seeded two-stage OPCPA using an evolutionary strategy to reliably reach an optimized working point. We use the data collected during the tuning procedure to calibrate a performance model of the laser system, which we then apply to stabilize the intricately coupled laser output energy and spectrum simultaneously. Our approach ensures reliable day-to-day operation at optimized working points without manual tuning. We demonstrate shot-to-shot energy stability of <0.18 % rms, in combination with <25 pm rms wavelength stability and <0.2 % rms bandwidth stability during multi-day operation.

Single-shot, high-repetition rate carrier-envelope-phase detection of ultrashort laser pulses.

We propose a single-shot, high-repetition rate measurement scheme of the carrier-envelope phase offset of ultrashort laser pulses. The spectral fringes resulting from f-2f nonlinear interferometry, encoding the carrier-envelope-phase, are evaluated completely optically via an optical Fourier transform. For demonstration, the carrier-envelope-phase of a 200 kHz, few-cycle optical parametric chirped-pulse amplification (OPCPA) laser system was measured employing an interferometer as a periodic optical filter. The proposed method shows excellent agreement with simultaneous measurement of the spectral fringes by a fast line-scan camera.

Sub-picosecond tunable mid-infrared light source for driving high-efficiency optical rectification.

Optical rectification (OR) is a popular way to generate coherent terahertz radiation. Here, we develop a sub-picosecond mid-infrared (mid-IR) light source with a tailored wavelength and pulse duration for enhancing the OR efficiency. Numerical simulations for a LiNbO3-based OR with tilted pulse-front excitation are first conducted to determine the optimal parameters of pump wavelength and pulse duration, demonstrating that the OR efficiency pumped by 4-µm sub-picosecond (0.5-0.6 ps) pulses is approximately twice the value with 0.8-µm pump at the same conditions. Guided by the simulation results, we build a BaGa4Se7-based optical parametric chirped-pulse amplification system with 1030-nm thin-disk pump and broadband mid-IR seeds. The output performances of >200-µJ pulse energy, ∼600-fs pulse duration and 1-kHz pulse repetition rate are achieved in a spectral range tunable from 3.5 to 5 µm. The large energy scalability and high parameter tunability make the light source attractive to high-efficiency OR in various materials.

49 W carrier-envelope-phase-stable few-cycle 2.1 µm OPCPA at 10 kHz.

We demonstrate a mid-infrared optical parametric chirped pulse amplifier (OPCPA), delivering 2.1 µm center wavelength pulses with 20 fs duration and 4.9 mJ energy at 10 kHz repetition rate. This self-seeded system is based on a kW-class Yb:YAG thin-disk amplifier driving a CEP stable short-wavelength-infrared (SWIR) generation and three consecutive OPCPA stages. Our SWIR source achieves an average power of 49 W, while still maintaining excellent phase and average power stability with sub-100 mrad carrier-envelope-phase-noise and 0.8% average power fluctuations. These parameters enable the OPCPA setup to drive attosecond pump probe spectroscopy experiments with photon energies in the water window.

Final amplifier of an ultra-intense all-OPCPA system with 13-J output signal energy and 41% pump-to-signal conversion efficiency.

Optical parametric chirped-pulse amplification (OPCPA) using high-energy Nd:glass lasers has the potential to produce ultra-intense pulses (>1023 W/cm2). We report on the performance of the final high-efficiency amplifier in an OPCPA system based on large-aperture (63 × 63-mm2) partially deuterated potassium dihydrogen phosphate (DKDP) crystals. The seed beam (180-nm bandwidth, 110 mJ) was provided by the preceding OPCPA stages. A maximum pump-to-signal conversion efficiency of 41% and signal energy up to 13 J were achieved with a 52-mm-long DKDP crystal due to the flattop super-Gaussian pump beam profile and flat-in-time pulse shape.

Generation and characterization of intense terahertz pulses from DSTMS crystal.

Matter manipulation in terahertz range calls for a strong-field broadband light source. Here, we present a scheme for intense terahertz generation from DSTMS crystal driven by a high power optical parametric chirped pulse amplifier. The generated terahertz energy is up to 175 µJ with a peak electric field of 17 MV/cm. The relationship between terahertz energy, conversion efficiency, and pump fluence is demonstrated. This study provides a powerful driving light source for strong-field terahertz pump-probe experimentation.

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.