Spectral Pulse Shaping Research Articles

Numerical investigation of the fractional-soliton mode-locked fiber laser.

We propose and numerically investigate a fractional-soliton mode-locked fiber laser by utilizing an intracavity spectral pulse shaper (SPS). The fiber laser can generate stable fractional-soliton pulses for three different Lévy index α (1 < α < 2), whose profiles are all close to the sech shape. We find that the positions of Kelly sidebands, pulse energy, and peak power of the emitted fractional pulses conform to three theoretical expressions, respectively. The numerical results are in good agreement with the theoretical analyses. In addition, the intracavity dynamics of the fractional pulses have been discussed. Our findings not only deepen the fundamental understanding of temporal fractional soliton but also provide a novel, to the best of our knowledge, approach to generating stable ultrashort fractional pulses.

Spectral phase pulse shaping reduces ground state depletion in high-order harmonic generation

High-order harmonic generation (HHG) has become an indispensable process for generating attosecond pulse trains and single attosecond pulses used in the observation of nuclear and electronic motion. As such, improved control of the HHG process is desirable, and one such possibility for this control is through the use of structured laser pulses. We present numerical results from solving the one-dimensional time-dependent Schrödinger equation for HHG from hydrogen using Airy and Gaussian pulses that differ only in their spectral phase. Airy pulses have identical power spectra to Gaussian pulses, but different spectral phases and temporal envelopes. We show that the use of Airy pulses results in less ground state depletion compared to the Gaussian pulse, while maintaining harmonic yield and cutoff. Our results demonstrate that Airy pulses with higher intensity can produce similar HHG spectra to lower intensity Gaussian pulses without depleting the ground state. The different temporal envelopes of the Gaussian and Airy pulses lead to changes in the dynamics of the HHG process, altering the time-dependence of the ground state population and the emission times of the high harmonics.Graphical abstractHigh-order harmonic generation (HHG) using an Airy pulse with a third order spectral phase results in less ground state depletion, but similar harmonic yield, compared to a Gaussian pulse. Top – schematic depiction of the 3-step HHG process for different intensity pulses. Bottom left – time-dependent ground state populations for Gaussian pulses showing that a more intense pulse causes more ground state depletion. Bottom middle – final ground state populations for Airy and Gaussian pulses as a function of intensity showing that Airy pulses result in less ground state depletion for a given intensity. Bottom right – HHG spectra for a more intense Airy pulse and a less intense Gaussian pulse exhibit similar shapes, magnitudes, and plateau cutoff values

Pure-high-even-order dispersion bound solitons complexes in ultra-fast fiber lasers

Temporal solitons have been the focus of much research due to their fascinating physical properties. These solitons can form bound states, which are fundamentally crucial modes in fiber laser and present striking analogies with their matter molecules counterparts, which means they have potential applications in large-capacity transmission and all-optical information storage. Although traditionally, second-order dispersion has been the dominant dispersion for conventional solitons, recent experimental and theoretical research has shown that pure-high-even-order dispersion (PHEOD) solitons with energy-width scaling can arise from the interaction of arbitrary negative-even-order dispersion and Kerr nonlinearity. Despite these advancements, research on the bound states of PHEOD solitons is currently non-existent. In this study, we obtained PHEOD bound solitons in a fiber laser using an intra-cavity spectral pulse shaper for high-order dispersion management. Specifically, we experimentally demonstrate the existence of PHEOD solitons and PHEOD bound solitons with pure-quartic, -sextic, -octic, and -decic dispersion. Numerical simulations corroborate these experimental observations. Furthermore, vibrating phase PHEOD bound soliton pairs, sliding phase PHEOD bound soliton pairs, and hybrid phase PHEOD bound tri-soliton are discovered and characterized. These results broaden the fundamental understanding of solitons and show the universality of multi-soliton patterns.

Experimental observation of linear pulses affected by high-order dispersion.

We experimentally study the linear propagation of optical pulses affected by high-order dispersion. We use a programmable spectral pulse-shaper that applies a phase that equals that which would result from dispersive propagation. The temporal intensity profiles of the pulses are characterized using phase-resolved measurements. Our results are in very good agreement with previous numerical and theoretical results, confirming that for high dispersion orders m the central part of the pulses follow the same evolution, with m only determining the rate of evolution.

Manipulating Explosion Dynamics of Dissipative Soliton in an Ultrafast Fiber Laser with Dynamic Dispersion Engineering

AbstractAs one of the most fascinating phenomena in dissipative systems, soliton explosions have been intensively investigated in the field of nonlinear optics owing to their intriguing dynamics. However, few efforts have been dedicated to precisely manipulating the dynamics of soliton explosion in fiber lasers. Herein, the exploding dynamics of dissipative soliton in a passively mode‐locked fiber laser by engineering the intracavity dispersion with a spectral pulse shaper is investigated. It is found that the exploding interval of the dissipative soliton can be well manipulated by dynamically engineering the cavity dispersion. The real‐time spectral dynamics of the soliton explosions are investigated by virtue of the dispersion Fourier transform (DFT) technique. The experimental results are further reproduced by the numerical simulations. These findings demonstrated that the dispersion engineering approach is a promising way to manipulate the soliton exploding behavior, and will also shed new light into the dynamics of soliton explosions in dissipative optical systems.

General Form of the Power Spectral Density of Multicarrier Signals

Multicarrier modulation has been adopted in many modern communication systems because of its many appealing properties. Its relatively high out-of-band radiation has spurred many techniques to shape the power spectral density (PSD) of multicarrier signals, including spectral precoding and pulse shaping. We derive a general expression for the PSD which is valid for subcarrier-specific pulses and for spectral precoders operating over multiple blocks. The only statistical assumptions on the vector-valued sequence modulating the active subcarriers are wide-sense cyclostationarity and properness. The applicability of the result to a number of popular multicarrier formats is discussed.

Pinpointing the macroscopic signatures of attosecond transient absorption in helium: Reshaped spectral splitting and persistent quantum beating

Although attosecond transient absorption spectroscopy (ATAS) has been widely used in the study of ultrafast dynamics of atoms, molecules, and solids, there is a need for further theoretical exploration of macroscopic effects beyond the response of single atoms. Here, the extreme ultraviolet (XUV) absorbance of He atoms in the presence of a delayed near-infrared (NIR) pulse is studied theoretically, from the limit of dilute-gas medium to high densities. By numerically solving the time-dependent Schr\"odinger equation coupled with Maxwell's equations, we elucidate the macroscopic signatures in the absorption spectrum of an optically dense medium, including previously recognized XUV spectral pulse shaping, a complex spectral splitting, and a persistent quantum beating, based on the energies of the states involved. An analytical expression for optical density is deduced directly to pinpoint the physical origins of the various absorption features in a quantitative way, which helps one grasp the intuitive picture of the macroscopic absorption spectrum and provides guidance to explore applications such as optical pulse shaping and XUV molecular quantum beat spectroscopy.

Spectral and temporal shaping of spectrally incoherent pulses in the infrared and ultraviolet.

Laser-plasma instabilities (LPIs) hinder the interaction of high-energy laser pulses with targets. Simulations show that broadband spectrally incoherent pulses can mitigate these instabilities. Optimizing laser operation and target interaction requires controlling the properties of these optical pulses. We demonstrate closed-loop control of the spectral density and pulse shape of nanosecond spectrally incoherent pulses after optical parametric amplification in the infrared (∼1053 nm) and sum-frequency generation to the ultraviolet (∼351 nm) using spectral and temporal modulation in the fiber front end. The high versatility of the demonstrated approaches can support the generation of high-energy, spectrally incoherent pulses by future laser facilities for improved LPI mitigation.

Temporal shaping of narrow-band picosecond pulses via noncolinear sum-frequency mixing of dispersion-controlled pulses

A long-sought-after goal for photocathode electron sources has been to improve performance by temporally shaping the incident excitation laser pulse. The narrow bandwidth, short wavelength, and picosecond pulse duration make it challenging to employ conventional spectral pulse shaping techniques. We present a novel and efficient intensity-envelope shaping technique achieved during nonlinear upconversion through opposite-chirp sum-frequency mixing. We also present a numerical case study of the linac coherent light source-II photoinjector where transverse electron emittance is improved by at least 25%.

Infinite hierarchy of solitons: Interaction of Kerr nonlinearity with even orders of dispersion

The authors demonstrate the existence of optical solitons arising from the balance between self-phase modulation and negative, pure, even high-order dispersion using a fiber laser incorporating a spectral pulse shaper.

The pure-quartic soliton laser

Ultrashort pulse generation hinges on the careful management of dispersion. Traditionally, this has exclusively involved second-order dispersion, with higher-order dispersion treated as a nuisance to be minimized. Here, we show that this higher-order dispersion can be strategically leveraged to access an uncharted regime of ultrafast laser operation. In particular, our mode-locked laser—with an intracavity spectral pulse shaper—emits pure-quartic soliton pulses that arise from the interaction of fourth-order dispersion and the Kerr nonlinearity. Phase-resolved measurements demonstrate that their pulse energy scales with the third power of the inverse pulse duration. This implies a strong increase in the energy of short pure-quartic solitons compared with conventional solitons, for which the energy scales as the inverse of the pulse duration. These results not only demonstrate a novel approach to ultrafast lasers, but more fundamentally, they clarify the use of higher-order dispersion for optical pulse control, enabling innovations in nonlinear optics and its applications. By suppressing the second- and third-order intracavity dispersion using an intracavity spectral pulse shaper, a mode-locked laser that emits pure-quartic soliton pulses that arise from the interaction of the fourth-order dispersion and the Kerr nonlinearity is demonstrated.

ADC Nonlinearity Correction for the Majorana Demonstrator

Imperfections in analog-to-digital conversion (ADC) cannot be ignored when signal digitization requirements demand both wide dynamic range and high resolution, as is the case for the Majorana Demonstrator <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">76</sup> Ge neutrinoless double-beta decay search. Enabling the experiment's high-resolution spectral analysis and efficient pulse shape discrimination required careful measurement and correction of ADC nonlinearities. A simple measurement protocol was developed that did not require sophisticated equipment or lengthy data-taking campaigns. A slope-dependent hysteresis was observed and characterized. A correction applied to digitized waveforms prior to signal processing reduced the differential and integral nonlinearities by an order of magnitude, eliminating these as dominant contributions to the systematic energy uncertainty at the double-beta decay Q value.

ZICOS - Neutrinoless Double Beta Decay experiment using Zr-96 with an organic liquid scintillator -

A liquid scintillator containing a tetrakis(isopropyl acetoacetato)zirconium has been developed for ZICOS experiment. In order to reach the sensitivity years, we have to use tone scale of 96Zr and have to reduce 95 % of backgrounds from 208Tl decay, which should be major backgrounds observed around Q-value (3.35 MeV) of 96 Zr neutrinoless double beta decay. According to the Monte Carlo simulation, we demonstrated that new method using the topological information of Cherenkov light could reduce 93 % of 208Tl background with 78 % efficiency for 0vββ signal. For an identification of Cherenkov light, the precise spectral pulse shape from both Cherenkov and scintillation was directly measured by using sub-MeV electrons from 90Sr/90Y beta source. The observed pulse rise and fall (decay) time for Cherenkov light were 0.8 ns and 2.5 ns, respectively. They were actually shorter than those times of scintillation light which were also measured by 1.6 ns and 6.5 ns, respectively. This clear difference of rise time will be used for the pulse shape discrimination in order to select photomultiplier tube which receives Cherenkov lights, and the topological information of Cherenkov light will be used for the reduction of backgrounds from 208Tl decay.

Coherent light matter interactions in nanostructure based active semiconductor waveguides operating at room temperature

Light matter coherent interactions require that the coherent state induced in the matter be maintained for the duration of the observation. The only way to induce and observe such interactions in room temperature semiconductors, where the coherence time is of the order of a few hundred femtoseconds, is to use ultrashort pulse excitations and an ultrafast characterization technique. For media comprising an ensemble of nanostructure semiconductors such as self-assembled quantum dots, the gain broadening inhomogeneity also affects the interaction. Moreover, when gain media in the form of an active waveguide, such as optical amplifiers, are used, the interaction is distributed and includes nonresonant incoherent phenomena that occur simultaneously with the coherent effects. Such a complex system can exhibit, nevertheless, clear coherent interactions even at room temperature. Using InAs/InP quantum dot and wirelike quantum dash amplifiers, Rabi oscillations, self-induced transparency, coherent control using spectral pulse shaping, Ramsey interference, and photon echo have been demonstrated. The characterization employed cross frequency resolved optical gating, and the experiments were accompanied by a comprehensive finite difference time domain model that solves the Maxwell and Lindblad equations. This work has major implications on the understanding of the details of dynamical processes in active semiconductor devices, on short pulse generation from semiconductor lasers, and on various future quantum devices.

Inside Cover: Fingerprint‐to‐CH stretch continuously tunable high spectral resolution stimulated Raman scattering microscope (J. Biophotonics 9/2019)

A novel design of an SRS microscope exploiting spectral pulse shaping allows measurement of fingerprint to CH‐stretch SRS spectra without any modification of the optical setup. High spectral resolution over a broad vibrational range allows label‐free quantitative imaging of biological samples. An exemplary SRS broadband spectrum of lipid droplets in a liver cancer cell is shown in the picture.Further details can be found in the article by Sergey P. Laptenok, Vijayakumar P. Rajamanickam, Luca Genchi, et al. (e201900028). image

Spectral efficient pulse shape design for UWB communication with reduced ringing effect and performance evaluation for IEEE 802.15.4a channel

Ultra-Wideband (UWB) faces some regulations due to the interference issues with the co-existing narrowband communication systems, due to which the effective utilization of bandwidth is not possible that causes lower data rate of transmission. We propose a pulse shaping method which can curtail the interference with the co-existing band of communication and have an ability to depress the ringing oscillation. The modified pulse shape has an ability to control over the transmitted power spectral density and offers improved antenna power resolution. To obtain the specific results, the seventh derivative of Gaussian pulse is used as a basic pulse. This pulse is spectrally modified by windowing with Gaussian window to achieve the desired performance. The analysis is not only limited to spectral management but also inculcate the performance estimation of the resultant pulse in multi-user scenario for indoor multipath channel IEEE 802.15.4a. We have also analysed the modified pulse to prove its ability in the location accuracy improvement for high-end application of UWB communication.

Generation of millijoule few-cycle pulses at 5 μm by indirect spectral shaping of the idler in an optical parametric chirped pulse amplifier

Spectral pulse shaping in a high-intensity midwave-infrared (MWIR) optical parametric chirped pulse amplifier (OPCPA) operating at 1 kHz repetition rate is reported. We successfully apply a MWIR spatial light modulator (SLM) for the generation of ultrashort idler pulses at 5 μm wavelength. Only bulk optics and active phase control of the 3.5 μm signal pulses via the SLM are employed for generating compressed idler pulses with a duration of 80 fs. The 80-fs pulse duration corresponds to less than five optical cycles at the central wavelength of 5.0 μm. The pulse energy amounts to 1.0 mJ, which translates into a peak power of 10 GW. The generated pulse parameters represent record values for high-intensity MWIR OPCPAs.

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.

Optimal design of waveform digitisers for both energy resolution and pulse shape discrimination

Fast digitisers and digital pulse processing have been widely used for spectral application and pulse shape discrimination (PSD) owing to their advantages in terms of compactness, higher trigger rates, offline analysis, etc. Meanwhile, the noise of readout electronics is usually trivial for organic, plastic, or liquid scintillator with PSD ability because of their poor intrinsic energy resolution. However, LaBr3(Ce) has been widely used for its excellent energy resolution and has been proven to have PSD ability for alpha/gamma particles. Therefore, designing a digital acquisition system for such scintillators as LaBr3(Ce) with both optimal energy resolution and promising PSD ability is worthwhile. Several experimental research studies about the choice of digitiser properties for liquid scintillators have already been conducted in terms of the sampling rate and vertical resolution. Quantitative analysis on the influence of waveform digitisers, that is, fast amplifier (optional), sampling rates, and vertical resolution, on both applications is still lacking. The present paper provides quantitative analysis of these factors and, hence, general rules about the optimal design of digitisers for both energy resolution and PSD application according to the noise analysis of time-variant gated charge integration.

Direct control of mode-locking states of a fiber laser

Mode locking is a non-equilibrium steady state. Capability to control mode-locking states can be used to improve performance as well as shed light on non-equilibrium physics using the laser as an experimental platform. We demonstrate direct control of the mode-locking state using spectral pulse shaping by incorporating a spatial light modulator at a Fourier plane inside the cavity of an Yb-doped fiber laser. We show that we can halt and restart mode locking, suppress instabilities, induce controlled reversible and irreversible transitions between mode-locking states, and perform advanced pulse shaping while using pulses as short as 40 fs.