Acousto-optic Programmable Dispersive Filter Research Articles

Ultrashort near-infrared pulse generation by non-collinear optical parametric amplification in LiInS2

We demonstrate non-collinear optical parametric amplification (NOPA) in LiInS2 to generate ultrashort near-infrared pulses. White light pulses around 1400 nm generated in yttrium aluminum garnet are amplified by five orders of magnitude up to 1.0 µJ by three-stage NOPA in LiInS2. The dispersion of the amplified pulses is compensated by an acousto-optic programmable dispersive filter, resulting in the pulse compression down to 40 fs, which is 1.1 times the pulse width of the Fourier-transform limited pulse. The successful demonstration of NOPA in LiInS2 indicates the possibility as a new light source to obtain high peak intensity which enables us to access the regime of non-perturbative physics.

Carrier-envelope phase control of synthesized waveforms with two acousto-optic programmable dispersive filters.

We demonstrate the scanning and control of the carrier-envelope phases (CEPs) of two adjacent spectral components totally spanning more than one-octave in the short-wave infrared (SWIR) wavelength region by operating two individual acousto-optic programmable dispersive filters (AOPDFs) applied to each of the two spectral components. The total CEP shift of the synthesized sub-cycle pulse composed of the two spectral components is controlled with simultaneous scans of the two CEPs. The resultant error of the controlled CEP was 642 mrad, so that this technique is useful for searching zero CEP of the synthesized pulse with the maximum field amplitude. In addition, we conduct a closed feedback loop to compensate for the CEP fluctuation by using the two AOPDFs together. As a result, we succeed to reduce the rms error of the CEP from 399 mrad to 237 mrad.

Proton beam quality enhancement by spectral phase control of a PW-class laser system

We report on experimental investigations of proton acceleration from solid foils irradiated with PW-class laser-pulses, where highest proton cut-off energies were achieved for temporal pulse parameters that varied significantly from those of an ideally Fourier transform limited (FTL) pulse. Controlled spectral phase modulation of the driver laser by means of an acousto-optic programmable dispersive filter enabled us to manipulate the temporal shape of the last picoseconds around the main pulse and to study the effect on proton acceleration from thin foil targets. The results show that applying positive third order dispersion values to short pulses is favourable for proton acceleration and can lead to maximum energies of 70 MeV in target normal direction at 18 J laser energy for thin plastic foils, significantly enhancing the maximum energy compared to ideally compressed FTL pulses. The paper further proves the robustness and applicability of this enhancement effect for the use of different target materials and thicknesses as well as laser energy and temporal intensity contrast settings. We demonstrate that application relevant proton beam quality was reliably achieved over many months of operation with appropriate control of spectral phase and temporal contrast conditions using a state-of-the-art high-repetition rate PW laser system.

Frequency-domain two-dimensional infrared spectroscopy using an acousto-optic programmable dispersive filter.

We report on multidimensional spectroscopy in the mid-infrared, performed using a calomel-based acousto-optic programmable dispersive filter. Although the associated spectral resolution is currently not as good as what has been previously reported using time-domain interferometers or other pulse-shaping technologies, the extreme compactness of the calomel crystal allows a straightforward implementation in a pre-existing pump-probe setup. Furthermore, the frequency-domain approach allows easy measurement of 2D slices of the multidimensional spectrum associated with a given pump frequency. We demonstrate our method with the measurement of the mid-infrared spectrum of carboxy-hemoglobin in three spectro-temporal dimensions.

Femtosecond supercontinuum generation in scattering media

We report our results on the effect of random multiple scattering on supercontinuum (SC) generation by intense light pulses. Spectral measurements are performed on the SC generated when femtosecond laser pulses propagate in water containing randomly suspended microspheres. We observed that the SC emission in the presence of scatterers is significantly suppressed in the blue side of the spectrum in comparison to that observed in neat water. We attribute this to the dissipation of incident energy, strong scattering of the shorter wavelengths, and stretching of the pulse temporally. This reasoning is supported by our experiments in neat water where we alter the shape of the incident femtosecond pulse by means of an acousto-optic programmable dispersive filter, and find similar suppression in the blue side with the lengthening of the input pulse. We believe our study will help in understanding the physics governing applications that involve transmission of high-intensity ultrashort pulses through long distances in scattering media like the atmosphere and sea water.

Dispersion control for temporal contrast optimization

We investigate the temporal contrast of the Light Wave Synthesizer 20 (LWS-20): a powerful, few-cycle source based on the optical parametric synthesizer principle. Saturation effects in the RF amplifier driving the acousto-optic programmable dispersive filter (AOPDF) were found to degrade the coherent contrast for non-monotonic group delay corrections. We subsequently present a new dispersion scheme and design a novel transmission grism-based stretcher optimized for LWS-20. The resulting temporal contrast of the amplified, compressed output pulses is improved by 2-4 orders of magnitude compared to the former design.

Towards Terawatt Sub-Cycle Long-Wave Infrared Pulses via Chirped Optical Parametric Amplification and Indirect Pulse Shaping

We present an approach for both efficient generation and amplification of 4–12 μm pulses by tailoring the phase matching of the nonlinear crystal Zinc Germanium Phosphide (ZGP) in a narrowband-pumped optical parametric chirped pulse amplifier (OPCPA) and a broadband-pumped dual-chirped optical parametric amplifier (DC-OPA), respectively. Preliminary experimental results are obtained for generating 1.8–4.2 μm super broadband spectra, which can be used to seed both the signal of the OPCPA and the pump of the DC-OPA. The theoretical pump-to-idler conversion efficiency reaches 27% in the DC-OPA pumped by a chirped broadband Cr2+:ZnSe/ZnS laser, enabling the generation of Terawatt-level 4–12 μm pulses with an available large-aperture ZGP. Furthermore, the 4–12 μm idler pulses can be compressed to sub-cycle pulses by compensating the tailored positive chirp of the idler pulses using the bulk compressor NaCl, and by indirectly controlling the higher-order idler phase through tuning the signal (2.4–4.0 μm) phase with a commercially available acousto-optic programmable dispersive filter (AOPDF). A similar approach is also described for generating high-energy 4–12 μm sub-cycle pulses via OPCPA pumped by a 2 μm Ho:YLF laser.

4-W, 100-kHz, few-cycle mid-infrared source with sub-100-mrad carrier-envelope phase noise.

We demonstrate an optical parametric chirped-pulse amplifier delivering 4-cycles (38-fs) pulses centered around 3.1 µm at 100-kHz repetition rate with an average power of 4 W and an undersampled single-shot carrier-envelope phase noise of 81 mrad recorded over 25 min. The amplifier is pumped by a ~1.1 ps, Yb-YAG, thin-disk regenerative amplifier and seeded with a supercontinuum generated in bulk YAG from the same pump pulses. Carrier-envelope phase stability is passively achieved through difference-frequency generation between pump and seed pulses. An additional active stabilization at 10 kHz combining 2f-to-f interferometry and a LiNbO3 acousto-optic programmable dispersive filter achieves a record low phase noise.

High-energy two-cycle pulses at 3.2 μm by a broadband-pumped dual-chirped optical parametric amplification.

A design for efficient generation of mid-infrared pulses at 3.2 μm is presented, which is based on numerical simulations of the broadband-pumped dual-chirped optical parametric amplification (DC-OPA) in LiNbO3 doped with 5 mol.% MgO (MgO:LiNbO3). The broadband seed can be generated by difference frequency generation in KTA using spectrally-broadened Ti:Sapphire lasers. The broad DC-OPA phase-matching bandwidth-spanning from 2.4 μm to 4.0 μm-is achieved by chirping both the broadband Ti:Sapphire pump pulses and the seed pulses in such a way that the individual temporal slice of pump spectrum is able to phase match that of seed spectrum. This phase matching scheme allows the use of longer crystals without gain narrowing or loss of conversion efficiency. The theoretical conversion efficiency from the pump to the idler reaches 19.1 %, enabling generation of a few hundred mJ of mid-IR energy with an available large-aperture MgO:LiNbO3 crystal. Furthermore, the commercially available acousto-optic programmable dispersive filter (AOPDF) ensures compression of such a broad bandwidth down to 20 fs (two optical cycles at 3.2 μm).

Improved pulse contrast on the Texas Petawatt Laser

We have completed a pulse contrast upgrade on the Texas Petawatt Laser. This improvement enables the use of thin and reduced mass targets for ion acceleration, and reduces pre-plasma effects on all experiments. The new design starts with two BBO-based OPCPA stages pumped by an optically synchronized 8-ps laser. These stages amplify slightly chirped few ps pulses by six orders of magnitude. Next there are two LBO-based OPCPA stages that are pumped by 4 ns pulses. With much less gain than before, parametric fluorescence has been reduced by about three orders of magnitude. Prior to the upgrade, lenses caused pencil beam prepulses. Since tilting or wedging lenses was not a viable option, we replaced all lenses in the glass amplifiers with off-axis parabolic mirrors. There are still weak prepulses that we attribute to surface scattering. We eliminated thin transmissive optics to avoid post pulses that would result in prepulses by nonlinear (B-integral) conversion. This required us to reduce from eight to four passes in the 64-mm glass amplifier and to add a two-pass 25-mm “booster amplifier.” As a final upgrade we added an Acousto-Optic Programmable Dispersive-Filter (AOPDF) to improve higher order dispersion and steepen the rising edge of the compressed pulse.

Kilohertz generation of high contrast polarization states for visible femtosecond pulses via phase-locked acousto-optic pulse shapers

We present a detailed analysis of a setup capable of arbitrary amplitude, phase, and polarization shaping of broadband visible femtosecond pulses at 1 kHz via a pair of actively phase stabilized acousto-optic programmable dispersive filters arranged in a Mach-Zehnder interferometer geometry. The setup features phase stability values around λ/225 at 580 nm as well as degrees of polarization of at least 0.9 for any polarization state. Both numbers are important metrics to evaluate a setup's potential for applications based on polarization-shaped femtosecond pulses, such as fully coherent multi-dimensional electronic spectroscopy.

Generation of ultrashort intense optical pulses at 1.6 μm from a bismuth triborate-based optical parametric chirped pulse amplifier with carrier-envelope phase stabilization

We describe a few-cycle intense optical parametric chirped pulse amplifier (OPCPA) in the IR that is based on bismuth triborate (BiB3O6, BIBO) crystals. Two Ti:sapphire chirped pulse amplification systems are used to generate seed and pump pulses for the OPCPA. Carrier-envelope phase (CEP)-stabilized seed pulses in the IR are produced by difference frequency mixing of white light spanning from the visible to near IR range. The seed pulses, which have a nearly one octave-spanning spectrum around 1.6 μm, are temporally stretched in an acousto-optic programmable dispersive filter and amplified up to 550 μJ in two BIBO-based parametric amplifiers without losing their bandwidth. After compression in a fused silica block, we obtained 9.2 fs optical pulses with a repetition rate of 1 kHz, which comprise less than two optical cycles at 1.6 μm. These optical pulses were used to generate extreme ultraviolet (XUV) high harmonics in krypton. We succeeded in measuring the CEP dependence of the XUV radiation near the silicon L edge around 100 eV, verifying the passive stabilization of the CEP of the sub-two cycle IR pulses. The XUV spectra consist of two half-cycle cutoffs and show a clear transition from a modulated structure to a continuum near the cutoff. The continuum-like spectra as well as their CEP dependence indicate that they originate in a single recombination burst, showing that few-cycle IR OPCPA light sources are capable of generating attosecond pulses in the XUV region.

Analysis the cross-polarized wave generation: Influence of the quadratic and cubic spectral phase with different pump energy fluence

In this paper, we present the comprehensive study of the influence of quadratic and cubic spectral phase on cross-polarized wave (XPW) generation, including conversion efficiency, spectrum broadening, and duration shortening with different pump energy fluence, using a sub-30fs laser pulse with 2-order supper Gaussian top-hat spectrum. This kind of broad top-hat spectrum, which would support very short fs pulse, can be obtained from acousto-optic programmable dispersive filter (AOPDF) technique. Different nonlinear processes that contribute to the generation of cross-polarized wave, including conversion efficiency and spectrum broadening, are theoretically compared. In addition, unlike the results given by previous authors, our analysis shows that the amount of XPW spectrum broadening relative to input linear chirp is asymmetric with respect to the zero chirp point, and the negative chirped pulse will result more spectral broadening compared to the pulse that has the same amount but positive chirp. We believe, our analysis presented here would result more in-depth of understanding about the XPW technique.

Visualization of high-order dispersion for compression of few-cycle pulses

We present a visually intuitive method for higher-order dispersion compensation based on multi-photon interpulse interference pulse scans. The dispersion values obtained from these scans are fed back as a correction to an acousto-optical programmable dispersive filter to compensate residual higher-order dispersions up to fifth order. This method is applied to the dispersion management of a non-collinear optical parametric chirped-pulse amplifier. A grism-pair stretcher is designed based on a global dispersion balance which provides a large stretching factor and supports a spectral bandwidth of up to 320 nm. It is implemented in a two-stage three-pass non-collinear optical parametric chirped-pulse amplifier and stretches 6-fs seed pulses to about 80 ps from 700 to 1,000 nm. The amplified pulses are compressed by material dispersion. Pulses of less than 10-fs duration with a pulse energy of 125 μJ are obtained at 20-kHz repetition rate.

Selective generation of ultracold high-density 1s orthoexcitons in Cu_2O with phase-modulated pulse using acousto-optic programmable filter

Ultracold and high-density 1s orthoexcitons in semiconductor cuprous oxide are prepared via resonant two-photon absorption of a phase-tailored femtosecond pulse, by utilizing an acousto-optic programmable dispersive filter. The stability of the quantum degenerate exciton gas is studied using excitonic Lyman spectroscopy. A density of 10(16) cm(-3) is realized without creating hot carriers, and the Lyman spectrum remains unchanged at this density. This result assures the stability of a spontaneous Bose-Einstein condensate of excitons at sub-Kelvin temperatures.

Pulse chirp effects in ultrafast laser-induced breakdown spectroscopy

When compared to many other sensitive methods for material detection, such as inductively coupled mass spectroscopy and thermal ionization mass spectroscopy, laser-induced breakdown spectroscopy (LIBS) typically exhibits a lower signal-to-noise ratio (SNR), resulting in higher detection limits. Increasing the SNR of LIBS would improve the ability to characterize the sample composition with increased accuracy and speed and reduce the amount of material needed to perform analysis. We have been investigating the effect of simple ultrashort laser pulse shaping on the SNR of LIBS. Our goal is to control the dynamics of the ionization and recombination processes in the laser-produced plasma to favorably affect the SNR associated with the line emission from the plasma. Pulse shaping is performed using an acousto-optic programmable dispersive filter. An adaptive learning algorithm is being developed to automate the pulse shape optimization process for maximization of LIBS SNR in nuclear security-relevant material characterization scenarios. We report a 27 % increase of the SNR for non-gated LIBS measurements of uranium by utilizing simple pulse shaping limited exclusively to excess quadratic spectral phase of the laser 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).

Remote sensing of trace gases with optical correlation spectroscopy and lidar: theoretical and numerical approach

In this paper, we propose a new active remote sensing methodology, based on laser spectroscopy, to evaluate the content of atmospheric trace gases. Its principle consists in coupling a lidar with optical correlation spectroscopy (OCS-lidar). Our theoretical and numerical studies show that OCS-lidar is a robust measurement methodology allowing trace gases environmental, agricultural, and industrial plants surveys. The novelty of this work is threefold. Firstly, we develop a new formalism to remotely evaluate the target gas concentration from optical correlation spectroscopy. Secondly, an acousto-optical programmable dispersive filter has been used to ensure that the lidar signal be spectrally correlated with the target gas of interest. It avoids using a hazardous gas reference cell, as operated in conventional OCS devices. Moreover, a clever spectral correlation is achieved since the contribution of absorption interfering species can then be minimized. Thirdly, to evaluate the performance of the OCS-lidar methodology, a numerical study of methane greenhouse gas is presented to evidence that atmospheric methane mixing ratios are retrievable over two orders of magnitude, from background level up to 100 ppb, within 100-m range resolution. Evaluation of the accuracy and the detection limit, including statistical and systematic errors assessment, are then objectively presented and discussed.

Spectral phase shift and residual angular dispersion of an acousto-optic programmable dispersive filter

Spectral phase shift and both types of wavelength dependent angular deviation introduced by an acousto-optic programmable dispersive filter (AOPDF) into a femtosecond laser beam at 800 nm have been measured with high precision. With the use of spectrally and spatially resolved interferometry, we have proved experimentally that the AOPDF controls the group delay dispersion (GDD) and third-order dispersion (TOD) with an accuracy of better than 1% and 3% of the preset values within the range of 10–1000 fs2 and 1000–40,000 fs3, respectively. The values of angular deviation and angular dispersion are primarily dependent on the set absolute value of GDD of the AOPDF when it is operating in continuous mode. Besides of a small offset value, there is no added angular dispersion at 0 fs2, while it can increase up to 0.2 μrad/nm at 10,000 fs2.

Direct shaping of picosecond high energy deep ultraviolet pulses

We demonstrate temporally shaped pulses in the deep ultraviolet spectral range (270 nm) with energies up to 37 μJ using an efficient prism stretcher and an acousto-optic programmable dispersive filter (AOPDF) applied directly in the UV. The scheme allows for arbitrary phase and amplitude shaping of picosecond UV pulses at high energy in a simple and efficient way.