Temporal Pump Research Articles

Few-femtosecond soft X-ray transient absorption spectroscopy with tuneable DUV-Vis pump pulses

Achieving few-femtosecond resolution for a pump-probe experiment is crucial to measuring the fastest electron dynamics and for creating superpositions of valence states in quantum systems. However, traditional UV-Vis pump pulses cannot achieve few-fs durations and usually operate at fixed wavelengths. Here, we present, to our knowledge, an unprecedented temporal resolution and pump tuneability for UV-Vis-pumped soft X-ray transient absorption spectroscopy. We have combined few-fs deep-UV to visible tuneable pump pulses from resonant dispersive wave emission in hollow capillary fiber with attosecond soft X-ray probe pulses from high harmonic generation. We achieve sub-5-fs time resolution, sub-fs interferometric stability, and continuous tuneability of the pump pulses from 230 to 700 nm. We demonstrate that the pump can initiate an ultrafast photochemical reaction and that the dynamics at different atomic sites can be resolved simultaneously. These capabilities will allow studies of the fastest electronic dynamics in a large range of photochemical, photobiological and photovoltaic reactions.

Fractional Fourier transform based on a temporal gradient-index lens

In this paper, an approach to realize all optical fractional Fourier transform through a high-nonlinear fiber and an optical pump is discussed. Based on a gradient index (GRIN) time lens which is realized through cross-phase modulation by a temporal quadratic pump pulse, it is possible to achieve all optical fractional Fourier transform. The order of the fractional Fourier transform varies along the fiber propagation distance. In a fixed fiber, it can be adjusted by simply changing the peak power of the pump pulse.

Ultrafast scanning electron microscopy with sub-micrometer optical pump resolution

Ultrafast scanning electron microscopy images carrier dynamics and carrier induced surface voltages using a laser pump electron probe scheme, potentially surpassing all-optical techniques in probe resolution and surface sensitivity. Current implementations have left a four order of magnitude gap between optical pump and electron probe resolution, which particularly hampers spatial resolution in the investigation of carrier induced local surface photovoltages. Here, we present a system capable of focusing the laser using an inverted optical microscope built into an ultrafast scanning electron microscopy setup to enable high numerical aperture pulsed optical excitation in conjunction with ultrafast electron beam probing. We demonstrate an order of magnitude improvement in optical pump resolution, bringing this to sub-micrometer length scales. We further show that temporal laser pump resolution can be maintained inside the scanning electron microscope by pre-compensating dispersion induced by the components required to bring the beam into the vacuum chamber and to a tight focus. We illustrate our approach using molybdenum disulfide, a two-dimensional transition metal dichalcogenide, where we measure ultrafast carrier relaxation rates and induced negative surface potentials between different flakes selected with the scanning electron microscope as well as on defined positions within a single flake.

Transient Super‐/Sub‐Linear Nonlinearities in Silicon Nanostructures (Advanced Optical Materials 5/2022)

In article number 2101711, Kung-Hsuan Lin, Shi-Wei Chu, and co-workers demonstrate a temporally tunable transient nonlinearity based on fluence-dependent carrier dynamics. This is exemplified via Auger recombination on silicon nanostructures. By combining spatial confocal x-scan and temporal pump–probe techniques, the fluence dependence is analyzed at different pump–probe delays and various transient nonlinearities are found, including sub-linear, super-linear, and surprisingly full saturation behaviors. [Cover image: artwork by Guan-Jie Huang.]

Raman Gain Square‐Wave Noise‐Like Pulse Laser Pumped by a Random Fiber Laser

AbstractMode locking of a long‐cavity Raman fiber laser pumped by a low‐noise random fiber laser (RFL) is demonstrated experimentally, where tunable square‐wave noise‐like pulse (NLP) is generated through nonlinear polarization rotation technology. Pulse duration can be tuned from 26 to 134 ns by controlling the polarization state or pump power at a repetition rate of 93 kHz. A signal‐to‐noise ratio of 64 dB is obtained due to the low‐noise characteristic of RFL. In addition, up to 24th high‐order harmonic mode‐locked square‐wave NLP is observed, which has not been reported in mode‐locked Raman fiber lasers with large normal dispersion. This approach not only provides a good temporal stable pump source for mode locking of Raman fiber lasers, but also enriches the methods of laser pulse generation and regulation.

Robust temporal pumping in a magneto-mechanical topological insulator

The transport of energy through 1-dimensional (1D) waveguiding channels can be affected by sub-wavelength disorder, resulting in undesirable localization and backscattering phenomena. However, quantized disorder-resilient transport is observable in the edge currents of 2-dimensional (2D) topological band insulators with broken time-reversal symmetry. Topological pumps are able to reduce this higher-dimensional topological insulator phenomena to lower dimensionality by utilizing a pumping parameter (either space or time) as an artificial dimension. Here we demonstrate a temporal topological pump that produces on-demand, robust transport of mechanical energy using a 1D magneto-mechanical metamaterial. We experimentally demonstrate that the system is uniquely resilient to defects occurring in both space and time. Our findings open a path towards exploration of higher-dimensional topological physics with time as a synthetic dimension.

Theory of coherent pump–probe spectroscopy in monolayer transition metal dichalcogenides

A valley-selective circular dichroism and a pronounced spin-valley locking in monolayer transition metal dichalcogenides (TMDCs) enable the investigation of new many-body physics revealed in the ultrafast nonlinear optical response of these atomically thin materials. While this topic is experimentally well studied in pump–probe spectroscopy, only a fragmented theoretical understanding is available due to the complexity and multitude of occurring effects. Here, a microscopic approach is presented to describe the ultrafast pump–probe response of monolayer TMDCs in the coherent limit. We focus on close to band edge excitations dominated by strongly correlated, bound electron–hole pairs, namely excitonic excitations. The approach includes Hartree–Fock and correlation effects up to two excitonic excitations known from conventional semiconductors as well as TMDC typical Coulomb mechanisms such as intra- and intervalley excitation and charge transfer. The investigated coherent limit is able to explain different signatures observed in ultrafast pump–probe spectroscopy for temporal pump–probe overlap within one consistent formalism dominated by excitons, biexcitons, and exciton-exciton scattering states.

Theoretical study of narrow-linewidth hybrid rare-earth-Raman fiber amplifiers.

In this paper, the spectral evolution properties and gain dynamics in hybrid rare-earth-Raman fiber amplifiers (H-RFAs) are demonstrated theoretically. Spectral broadening mechanisms and design strategies are given for H-RFAs based on two different types of pump schemes for generating the pump laser of Raman gain. As for the diode-pumped scheme, only a temporal stable pump laser of Raman gain is required to achieve the narrow-linewidth operation of an ultimate Raman fiber laser. As for the tandem-pumped scheme, both temporal stable pump lasers of rare-earth gain and Raman gain are required to achieve narrow-linewidth operation. The physical mechanism behind the phenomenon is the diversity of the pump-to-signal noise transfer property when applying different pump sources of rare-earth gain.

Laying the Foundation for Crassulacean Acid Metabolism (CAM) Biodesign: Expression of the C4 Metabolism Cycle Genes of CAM in Arabidopsis.

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that exploits a temporal CO2 pump with nocturnal CO2 uptake and concentration to reduce photorespiration, improve water-use efficiency (WUE), and optimize the adaptability of plants to hotter and drier climates. Introducing the CAM photosynthetic machinery into C3 (or C4) photosynthesis plants (CAM Biodesign) represents a potentially breakthrough strategy for improving WUE while maintaining high productivity. To optimize the success of CAM Biodesign approaches, the functional analysis of individual C4 metabolism cycle genes is necessary to identify the essential genes for robust CAM pathway introduction. Here, we isolated and analyzed the subcellular localizations of 13 enzymes and regulatory proteins of the C4 metabolism cycle of CAM from the common ice plant in stably transformed Arabidopsis thaliana. Six components of the carboxylation module were analyzed including beta-carbonic anhydrase (McBCA2), phosphoenolpyruvate carboxylase (McPEPC1), phosphoenolpyruvate carboxylase kinase (McPPCK1), NAD-dependent malate dehydrogenase (McNAD-MDH1, McNAD-MDH2), and NADP-dependent malate dehydrogenase (McNADP-MDH1). In addition, seven components of the decarboxylation module were analyzed including NAD-dependent malic enzyme (McNAD-ME1, McNAD-ME2), NADP-dependent malic enzyme (McNADP-ME1, NADP-ME2), pyruvate, orthophosphate dikinase (McPPDK), pyruvate, orthophosphate dikinase-regulatory protein (McPPDK-RP), and phosphoenolpyruvate carboxykinase (McPEPCK). Ectopic overexpression of most C4-metabolism cycle components resulted in increased rosette diameter, leaf area, and leaf fresh weight of A. thaliana except for McNADP-MDH1, McPPDK-RP, and McPEPCK. Overexpression of most carboxylation module components resulted in increased stomatal conductance and dawn/dusk titratable acidity (TA) as an indirect measure of organic acid (mainly malate) accumulation in A. thaliana. In contrast, overexpression of the decarboxylating malic enzymes reduced stomatal conductance and TA. This comprehensive study provides fundamental insights into the relative functional contributions of each of the individual components of the core C4-metabolism cycle of CAM and represents a critical first step in laying the foundation for CAM Biodesign.

Incoherent triggering of picosecond pulse pumped supercontinuum

ABSTRACTWe numerically study spectral and noise properties of picosecond pulse pumped supercontinuum using an incoherent continuous wave trigger with 1% pump intensity. We have swept the trigger central wavelength from 1404 to 1724 nm, and observe obvious improvement in the SC bandwidth and moderate enhancement of SNR when the ASE-based CW-trigger is located at a proper wavelength range. We also varied the trigger bandwidth from 0.5 to 6 nm and find a reduced effect of the trigger when its associated coherence time decreases below the duration of the temporal pump pulse. Finally, we have varied the pump pulse peak intensity from 20 W to 120 W to demonstrate the power dependency of the suggested CW triggering technique.

Highly efficient, cascaded extraction optical parametric amplifier.

The scheme of cascaded extraction optical parametric amplifier (CE-OPA) has been proposed as a final amplifier for high peak power laser systems. 4D numerical simulations show that conversion efficiency of a CE-OPA system pumped with a temporal Gaussian pump pulse is as close to the theoretical limit of quantum efficiency as a conventional OPA pumped with temporal flat-top pump pulse. The CE-OPA system is also similar to the conventional scheme in output energy stability and alignment sensitivity of the phase-matching angles, too. However, with the use of the CE-OPA scheme, the requirement of pump pulse shaping can be relaxed, leading to an overall higher plug in efficiency as well as compact design.

Topological magnetoelectric pump in three dimensions

We study the topological pump for a lattice fermion model mainly in three spatial dimensions. We first calculate the U(1) current density for the Dirac model defined in continuous space-time to review the known results as well as to introduce some technical details convenient for the calculations of the lattice model. We next investigate the U(1) current density for a lattice fermion model, a variant of the Wilson-Dirac model. The model we introduce is defined on a lattice in space but in continuous time, which is suited for the study of the topological pump. For such a model, we derive the conserved U(1) current density and calculate it directly for the $1+1$ dimensional system as well as $3+1$ dimensional system in the limit of the small lattice constant. We find that the current includes a nontrivial lattice effect characterized by the Chern number, and therefore, the pumped particle number is quantized by the topological reason. Finally we study the topological temporal pump in $3+1$ dimensions by numerical calculations. We discuss the relationship between the second Chern number and the first Chern number, the bulk-edge correspondence, and the generalized Streda formula which enables us to compute the second Chern number using the spectral asymmetry.

Resonant excitation of transverse patterns in broad-area lasers by periodic temporal pump modulation

We demonstrate numerically that the temporal periodic modulation of the pump can excite regular transverse spatiotemporal intensity patterns in broad-area lasers. The Floquet stability analysis is used to characterize dynamics of modulated systems. Pattern formation occurs when the modulation frequency is approximately equal to the relaxation frequency or twice the value of this frequency. Instability of homogeneous oscillations leads to the formation of regular optical patterns, such as stripes and hexagons. The characteristic sizes of the observed patterns are in good agreement with predictions of the Floquet analysis.

200 J high efficiency Ti:sapphire chirped pulse amplifier pumped by temporal dual-pulse.

We report on an experimental and theoretical study of a large-aperture Ti:Sapphire (Ti:S) amplifier pumped with a novel temporal dual-pulse scheme to suppress the parasitic lasing (PL) and transverse amplified spontaneous emission (TASE) for high-energy chirped-pulse amplification (CPA). The pump energy distribution was optimized and the time delay between each pump pulse was controlled precisely. Both the numerical and experimental results confirm that the temporal dual-pulse pump technique can effectively suppress PL and TASE. The maximum output energy of 202.8 J was obtained from the final 150-mm-diameter Ti:S booster amplifier with a pump energy of 320.0 J, corresponding to a conversion efficiency of 49.3%. The compressed pulse duration of 24.0 fs was measured with a throughput efficiency of 64%, leading to a peak power of 5.4 PW. This novel temporal dual-pulse pump technique has potential applications in a 10 PW CPA laser system.

Comparison of high-energy multi-pass Ti:sapphire amplifiers with a different Ti-dopant concentration

We experimentally compare the output abilities of lightly and heavily doped Ti:Sapphire (Ti:S) amplifiers with diameters as large as 150 mm. Although a lightly doped Ti:S is more favorable to overcome parasitic lasing (PL) and transverse amplified spontaneous emission (TASE), the self-phase-modulation (SPM) effect becomes more pronounced when a longer crystal is used. Recompression of the amplified, stretched pulses can be seriously affected by the SPM effect. We then propose a temporal multi-pulse pump scheme to suppress PL and TASE in a thin, heavily doped Ti:S crystal. This novel temporal multi-pulse pump technique can find potential applications in 10 PW chirped-pulse amplification laser systems.

Phase-mismatched localized fields in A-PPLN waveguide devices.

Highly phase-mismatched nonlinear interactions can generate spatially localized optical fields that can affect the performance of nonlinear optical devices. We present a theoretical description of the generation of such spatially localized optical fields by ultrafast pulses. The effects of temporal walk-off and pump depletion are discussed, along with methods for suppression of the localized field while maintaining the performance of the nonlinear device. The model is validated by the measurement of the spatial profile of the localized field in a quasi-phase-matched (QPM) aperiodically poled lithium niobate (A-PPLN) waveguide. Finally, we fabricate and characterize A-PPLN devices with a 33% duty cycle to reduce the locally generated field by 90%.

Nonphotochemical Laser-Induced Nucleation in Levitated Supersaturated Aqueous Potassium Chloride Microdroplets

We have observed nonphotochemical laser-induced nucleation (NPLIN) in levitated 8 pL microdroplets of supersaturated aqueous potassium chloride irradiated with nanosecond pulses of 532 nm light. A much higher supersaturation ratio S of 1.20 was required to observe NPLIN in a microdroplet, compared to the value of 1.06 for bulk solutions, attributed to a 40-million-fold lower nucleation rate in a microdroplet at S = 1.06 as a result of its much smaller volume. This finding has application to high spatial and temporal resolution pump–probe studies of nucleation in a containerless environment.

Engineering crassulacean acid metabolism to improve water-use efficiency.

Climatic extremes threaten agricultural sustainability worldwide. One approach to increase plant water-use efficiency (WUE) is to introduce crassulacean acid metabolism (CAM) into C3 crops. Such a task requires comprehensive systems-level understanding of the enzymatic and regulatory pathways underpinning this temporal CO2 pump. Here we review the progress that has been made in achieving this goal. Given that CAM arose through multiple independent evolutionary origins, comparative transcriptomics and genomics of taxonomically diverse CAM species are being used to define the genetic 'parts list' required to operate the core CAM functional modules of nocturnal carboxylation, diurnal decarboxylation, and inverse stomatal regulation. Engineered CAM offers the potential to sustain plant productivity for food, feed, fiber, and biofuel production in hotter and drier climates.

Theoretical model to suppress parasitic lasing in large-aperture Ti:sapphire amplifiers using a temporal dual-pulse pump

Transverse parasitic lasing (PL) in large-aperture Ti:sapphire (Ti:S) crystals is a critical factor that limits the energy achievable with the chirped-pulse amplification (CPA) technique. We propose a method to suppress PL effects in large-aperture Ti:S amplifiers by using a temporal dual-pulse pump. Theoretical simulations based on the experimental parameters in 2.0PW Ti:S laser system are performed to predict the transverse gain as a function of pumping time and output energy. By optimizing the temporal profile of the pump beam as well as the time delay between the input seed and pump pulses, we can minimize PL effects in Ti:S crystals. This method is applicable to larger-aperture Ti:S crystals pumped at higher pump fluence and energy, and is potential to develop a ~10PW laser system.

Optical data exchange of 100-Gbit/s DQPSK signals

We experimentally demonstrate the phase-transparent optical data exchange between two differential quadrature phase-shift keying (DQPSK) signals by exploiting the signal depletion effect of non-degenerate four-wave mixing (FWM) in a highly nonlinear fiber (HNLF). Identical phase modulation is applied to the two pumps to suppress the stimulated Brillouin scattering (SBS) effect and enable the pump phase cancellation in the exchanged signals. Optical data exchange of 100-Gbit/s return-to-zero DQPSK (RZ-DQPSK) signals is implemented with a power penalty of less than 5 dB at a bit-error rate (BER) of 10(-9). Moreover, we investigate the impact of the temporal pump phase misalignment on the exchange performance and the dynamic range of the input signal power for the 100-Gbit/s RZ-DQPSK data exchange. The tolerance of the temporal pump phase misalignment is assessed to be +/-2 ps. An approximate 20-dB dynamic range of the input signal power is achieved.