Temporal Magnification Research Articles

Time Lens Photon Doppler Velocimetry (TL-PDV) for extreme measurements

Capturing extreme surface velocities with >50 km/s dynamic range, which arise in shock physics such as inertial confinement fusion (ICF), is beyond the reach of conventional photon Doppler velocimetry (PDV) systems due to the need for extremely large electrical bandwidth under such conditions. The recent ignition in ICF calls for new velocimetry that can measure velocities exceeding 100 km/s. Time lens PDV (TL-PDV) is a solution where the high frequency beat signal from a conventional PDV system is periodically temporally magnified in the optical domain using a time lens. Here we experimentally demonstrate TL-PDV for the first time, validate the performance over a 74 km/s velocity range with high accuracy using a temporal magnification factor of 7.6, and verify excellent agreement with conventional PDV for laser driven micro-flyer experiments. TL-PDV currently provides the largest velocity dynamic range among PDV systems and is scalable to even higher velocities, which makes it an ideal candidate for material characterization under the most extreme conditions such as optimizing fuel efficiency in ICF experiments.

Characterization of the upgraded single-line-of-sight time-resolved x-ray imager using short-pulse visible and UV lasers.

The single-line-of-sight time-resolved x-ray imager (SLOS-TRXI), a fast-gated x-ray imager used for capturing x-ray self-emission in inertial confinement fusion experiments on OMEGA, has been upgraded and characterized. SLOS-TRXI combines an electron-dilation imager and a hybrid complementary metal-oxide-semiconductor (hCMOS) sensor to capture multiple gated frames on a single line of sight with a temporal resolution of ∼40ps and a spatial resolution of 10 µm. The original hCMOS sensor with four frames was replaced with a newer-generation hCMOS sensor having eight frames. Gate characterizations of both the sensor and the entire SLOS-TRXI diagnostic were performed using ∼10-ps FWHM visible (2ω) and UV (4ω) short-pulse lasers, respectively. A stepped echelon was used to generate a train of five UV laser pulses having an interpulse separation of 30 ± 3ps. Characterization results of the hCMOS gating (2.28 ± 0.02-ns FWHM on average) and a temporal resolution of the upgraded SLOS-TRXI (34 ± 4-ps FWHM on average) are presented. A temporal magnification for the electron-dilation imager between 40 and 60 was inferred from the characterization results. The spatial resolution of the upgraded SLOS-TRXI remains the same in light of this work.

Simulation of the temporal resolution uniformity of a dilation framing camera.

The temporal resolution uniformity of a time-dilation framing camera is studied, and the ideal photocathode (PC) pulse curve is determined, while the temporal magnification factor is kept constant. To obtain the ideal curve, a series of linear pulses with the same slope are superposed. The variance in the temporal resolution and the number of linear pulses required are compared, while the superposition results with different slopes are used as the PC voltage. As the slope of the linear pulses decreases, the variance decreases, which means that the uniformity of the temporal resolution is improved, but the number of linear pulses required increases. In this study, linear pulses with a slope of 1V/ps are superposed. Nine linear pulses with a front edge time of 200ps, amplitude of 200V, and flat top time of 1ns are superimposed to approximate the ideal PC pulse curve with a constant temporal magnification factor of 10; the trigger times of the pulses are 0, 0, 0, 185, 200, 350, 450, 605, and 790ps. When the superposition result is applied as the PC voltage and the measured signal is synchronized to the PC pulse at 128ps-1ns, the temporal resolution error is within 5%.

Bandwidth Compressed Time-Mapped Spectrogram Analysis Based on Temporal Talbot Effect and Temporal Magnification

A method to provide bandwidth compressed time-mapped spectrogram analysis based on temporal Talbot effect and temporal magnification is proposed and numerically demonstrated in this paper. The signal under test (SUT) is firstly sampled by a periodic pulse train, then passes through a dispersive medium under the Talbot condition and the spectrogram of the SUT is mapped to the time domain, so-called time-mapped spectrogram (TM-SP). Subsequently, a temporal magnification technique is implemented to stretch the time axis and compress the spectrum bandwidth, so that the effect of detection bandwidth on the frequency resolution is alleviated. Though the TM-SP cannot be acquired in a continuous way, the SUT is analyzed with ultrahigh frame rate in the temporal aperture. Additionally, a method to improve acquisition frame rate is proposed. The proposed bandwidth compressed TM-SP analysis is compared with the dispersion-based Fourier transform, and the related tradeoffs are provided in detail. The bandwidth compressed TM-SP analysis with a frequency resolution of 0.1 GHz, a measurable frequency range of 4.85 GHz, an analysis period of 0.1 ns, and an observation period of 4 ns is achieved by simulation.

Spectral-temporal transient dynamics of dissipative soliton molecules in mode-locking fiber lasers

Dissipative soliton molecules that are analogous in many ways to matter molecules manifest complex evolution dynamics. Here, spectral-temporal transient internal motion dynamics of dissipative soliton molecules generated in a passively mode-locking erbium-doped fiber laser are experimentally investigated. Various categories of internal motion dynamics including attraction, creeping, dual-period breathing, and collision behaviors are revealed by employing an asynchronous time lens-based temporal magnifier together with the time stretched technique. Soliton temporal separation in those motion dynamics exhibit gradual decreasing and slightly wiggling motion. The temporal magnification factor of time lens system is substantially improved into 361. Our work makes the temporal magnifier more attractive for the applications of ultrafast measurements and nonlinear fiber optics, and benefits for fiber laser design.

Difference-frequency chirped-pulse dual-comb generation in the THz region: Temporal magnification of the quantum dynamics of water vapor lines by >60 000.

A new difference-frequency method based on electro-optic phase modulators (EOMs) and two free-running lasers is reported to perform chirped-pulse dual-comb spectroscopy in the THz region. A variation of a near-IR interleaving scheme we recently reported has been developed to interleave the EOMs' orders and sidebands and to map THz comb teeth into the radio-frequency region below 1MHz. The down-converted comb teeth are shown to have transform limited widths of 1Hz over a 1s time scale. The dual chirp-pulsed scheme is used to measure the complex line shapes of two water vapor lines below 600GHz and to temporally magnify the effects of rapid passage by more than 60 000. For the 11,0 ← 10,1 transition in H2O, a pressure dependent phase perturbation is observed in the rapid passage response over the magnified time scale in contrast to a uniform line shape transformation observed for the 21,1 ← 20,2 transition of D2O. The possible origins for this anomalous behavior are modeled and discussed. The method is applicable to any region where difference or sum frequency waves can be generated.

Numerical study and improvement of the dynamic performance of dilation x-ray imager.

We present in this Note a numerical study on the dynamic performance of a Dilation X-ray Imager (DIXI). The DIXI including a photoelectron tube (PT) and a magnetic solenoid is modeled in 3D space. The initial parameters of the photoelectrons are sampled with a Monte Carlo code. The trajectories of the photoelectrons are calculated by using the particle-in-cell method, and the transit time spread (TTS) and temporal magnification are analyzed in detail. We have designed a PT with a double-microstrip structure and compared the performance of the double-microstrip PT with the traditional single-microstrip PT. The results show that the sensitivity of the TTS and the temporal magnification to the emission time of the photoelectrons can be significantly reduced by using the double-microstrip PT, resulting in an improvement of the time window. Therefore, the dynamic performance of the DIXI is improved.

Low-latency full-field temporal magnification based on spectral compression

Temporal magnification is an emerging technology for the observation of single-shot optical signals with irregular and ultrafast dynamics, which exceed the speed, precision, and record length of conventional digitizers. Conventional temporal magnification schemes suffer from transmission delay and large volume of dispersive elements. Because only the signal envelope can be magnified in the dispersion-based schemes, real-time full-field (phase and amplitude) measurement for a complex ultrafast optical signal remains an open challenge. Here, a bandwidth-compressed temporal magnification scheme for low-latency full-field measurements of ultrafast dynamics is proposed. Unlike the dispersion-based schemes, temporal magnification of a complex optical signal is achieved by bandwidth compression. The bandwidth is coherently compressed by the Vernier effect relying on the detuned free spectral range of a periodic optical filter and time lens. Experimentally, a temporal magnification factor of 224 is realized, and full-field measurements for picosecond pulses are demonstrated. The proposal eliminates the dependence on dispersive elements and shows great potential in integration, which may pave a new path toward full-field measurement for nonrepetitive and statistically rare signals.

Soliton Burst and Bi‐Directional Switching in the Platform with Positive Thermal‐Refractive Coefficient Using an Auxiliary Laser

AbstractDissipative Kerr solitons in optical microresonators enable the generation of stable ultrashort pulses and phase‐locked frequency combs, leading to their widespread applications. For traditional platforms with positive thermal‐refractive coefficient, strong thermal effect increases the difficulties of soliton triggering and prohibits the deterministic control of soliton number. Here, using an auxiliary laser to tune thermal effect, soliton burst and bi‐directional switching are demonstrated in high‐index doped silica glass platform. First, by varying the parameters of the auxiliary laser, the thermal effect tuning of the microresonator is studied with different thermal compensation states achieved, leading to distinct soliton switching features. Especially, the solitons burst and bi‐directional switch in over‐compensated state. The corresponding process is recorded in real time based on a temporal magnification system, uncovering transient dynamics from continuum background noise to soliton formation. Finally, the deterministic generation of solitons is enabled with controllable soliton number spanning from 1 to 21. The present work provides insight into soliton dynamics and enables soliton generation on demand with a large range of soliton numbers inside a single device.

Simulation of a pulse-dilation framing tube with sensitive diameter of 60 mm using large aperture short magnetic lens

A pulse-dilation framing tube with large aperture short magnetic lens is simulated by using Monte Carlo method. The photo-cathode (PC) sensitive diameter is 60 mm, and the image ratio is 2:1. While a -3.15 kV dc voltage overlap by an excitation pulse with gradient of 3 V/ps are applied on PC, a gating pulse with width of 225 ps and amplitude of -1.3 kV plus a −100 V dc bias are for the microchannel plate (MCP), the temporal resolution and spatial resolution are 7.8 ps, 11 lp/mm, respectively. The electron beam temporal magnification factor is about 10.3. The relationship between the spatial resolution and the PC electron beam emitting point is obtained. The variation of the temporal magnification factor and temporal resolution with the PC excitation pulse gradient is also given. Furthermore, the connection between the spatial resolution and the PC excitation pulse gradient is acquired.

Time-division-multiplexed observation bandwidth for ultrafast parametric spectro-temporal analyzer.

Parametric spectro-temporal analyzer (PASTA) has been demonstrated as a powerful tool for ultrafast spectrum measurement with superior frame rate and resolution. Compared with other time-stretch-based counterparts, the temporal focusing mechanism enlarges the initial condition and enables the observation of arbitrary waveform, especially the emission spectrum. However, due to the limited conversion bandwidth of the parametric mixing-based time-lens, the observation bandwidth of PASTA is constrained within the C (conventional) band, which hinders its practical applications. To overcome this constraint, both stokes and anti-stokes conversions of the parametric mixing process are leveraged, and the concept of time division multiplexing (TDM) is introduced to ensure their separability. Therefore, the TDM-based PASTA system successfully demultiplexes the C band and L (long) band spectra in two adjacent temporal frames. It is capable of reconstructing the wavelength-to-time sequence for arbitrary waveform over a record 58-nm observation bandwidth, which can be further improved by optimizing the filters and amplifiers. Meanwhile, both of these two bands achieve 20-pm resolution, 10-MHz frame rate, and -30-dBm sensitivity. Moreover, this TDM concept can also be applied to other parametric mixing-based temporal imaging systems to enlarge the working wavelength band, such as temporal magnification.

Influences of group velocity dispersion on ultrafast pulse shaping in time lens

Time-lens technology is of significant interest in signal processing and optical communication. The impacts of group velocity dispersion (GVD) on ultrafast pulse shaping in a time-lens system based on four-wave mixing are explored in this paper. The output signals of temporal magnification and time-to-frequency conversion under different GVDs are theoretically investigated in detail. The simulation results imply that the femtosecond pulse is sensitive to GVD in propagation. GVD has an important effect on nonlinear parametric processes, which results in output signals presenting different pulse shapes and different frequency profiles. Furthermore, a model of silicon nitride waveguide with flat dispersion is proposed by finite element method and signal processing with negligible pulse distortion is realized in near-infrared region.

Demutiplexing of Nyquist-OTDM Signal Based on Temporal Magnification Aided Optical Sampling With Enhanced Performance

Demultiplexing of high-speed Nyquist optical time-division multiplexed (N-OTDM) signal requires ultra-narrow local sampling pulse to avoid the severe inter-symbol-interference (ISI) between each tributary. Unfortunately, generation of such narrow sampling pulse is difficult or usually need complex setup configure at the receiver side, which would cause ineffective cost in application scenarios such as short-reach optical communication or PON applications. In this paper, we propose and demonstrate demultiplexing of N-OTDM signal based on temporal magnification followed by coherent optical sampling to enable broader sampling pulsewidths while reducing the ISI. The target tributary of the N-OTDM signal is temporally magnified and further demultiplexed through coherent optical sampling using Gaussian-shaped or Nyquist-shaped pulses. With the aid of temporal magnification based on a time-lens, the sampling window can be extended during the coherent detection progress at the receiver side. Gaussian sampling pulses with a pulsewidth up to 10.4 ps are enabled for the demultiplexing of a 160 Gbaud N-OTDM signal. Compared with demultiplexing based on Nyquist pulses (i.e., coherent matched sampling) without temporal magnification, the proposed scheme features a better performance with pulsewidths greater than 6 ps. If temporal magnification is combined with coherent matched sampling, Nyquist sampling pulses with a pulsewidth up to 12.4 ps are made possible for the demultiplexing. Therefore, the proposed scheme based on temporal magnification could significantly release the pulsewidth requirement for N-OTDM demultiplexing while mitigating the ISI.

Temporal magnification for streaked ultrafast electron diffraction and microscopy

One of the frontiers of modern electron scattering instrumentation is improving temporal resolution in order to enable the observation of dynamical phenomena at their fundamental time-scales. We analyze how a radiofrequency cavity can be used as an electron longitudinal lens in order to produce a highly magnified temporal replica of an ultrafast process, and, in combination with a deflecting cavity, enable streaked electron images of optical-frequency phenomena. We present start-to-end simulations of an MeV electron beamline for two variations of this idea (a “magnifying-glass” and a “point-projection” configuration) showing the feasibility for an electron probe to achieve single shot 1.4 fs(rms) temporal resolution.

Characterisation of a sub-20 ps temporal resolution pulse dilation photomultiplier tube.

A pulse-dilation photomultiplier tube (PD-PMT) with sub-20 ps temporal resolution has been developed for use with γ-ray-sensitive gas Cherenkov detectors at the National Ignition Facility to improve the diagnosis of nuclear fusion burn history and the areal density of the remaining capsule ablator. The pulse-dilation mechanism entails the application of a time-dependent, ramp waveform to a photocathode-mesh structure, introducing a time-dependent photoelectron accelerating potential. The electric field imparts axial velocity dispersion to outgoing photoelectrons. The photoelectron pulse is dilated as it transits a drift region prior to amplification in a microchannel plate and read out with a digital oscilloscope. We report the first measurements with the prototype PD-PMT demonstrating nominal <20 ps FWHM across a 400 ps measurement window and <30 ps FWHM for an extracted charge up to 300 pC. The output peak areas are linear to within 20% over 3 orders of magnitude of input intensity. 3D particle in cell simulations, which included space charge effects, have been carried out to investigate the device temporal magnification, resolution, and linearity.

Quantum simulation of ultrafast dynamics using trapped ultracold atoms

Ultrafast electronic dynamics are typically studied using pulsed lasers. Here we demonstrate a complementary experimental approach: quantum simulation of ultrafast dynamics using trapped ultracold atoms. Counter-intuitively, this technique emulates some of the fastest processes in atomic physics with some of the slowest, leading to a temporal magnification factor of up to 12 orders of magnitude. In these experiments, time-varying forces on neutral atoms in the ground state of a tunable optical trap emulate the electric fields of a pulsed laser acting on bound charged particles. We demonstrate the correspondence with ultrafast science by a sequence of experiments: nonlinear spectroscopy of a many-body bound state, control of the excitation spectrum by potential shaping, observation of sub-cycle unbinding dynamics during strong few-cycle pulses, and direct measurement of carrier-envelope phase dependence of the response to an ultrafast-equivalent pulse. These results establish cold-atom quantum simulation as a complementary tool for studying ultrafast dynamics.

Temporal and spectral manipulations of correlated photons using a time lens

A common challenge in quantum information processing with photons is the limited ability to manipulate and measure correlated states. An example is the inability to measure picosecond scale temporal correlations of a multi-photon state, given state-of-the-art detectors have a temporal resolution of about 100 ps. Here, we demonstrate temporal magnification of time-bin entangled two-photon states using a time-lens, and measure their temporal correlation function which is otherwise not accessible because of the limited temporal resolution of single photon detectors. Furthermore, we show that the time-lens maps temporal correlations of photons to frequency correlations and could be used to manipulate frequency-bin entangled photons. This demonstration opens a new avenue to manipulate and analyze spectral and temporal wavefunctions of many-photon states.

All-Optical Reconfigurable Signal Processing Based on Cross Phase Modulation Time Lensing

A system is proposed for all-optical reconfigurable time-to-frequency (T-to-F) conversion and temporal magnification of optical waveforms using a design based on a cross phase modulation-induced time lens combined with group-velocity dispersion. In this design, the T-to-F conversion ratio and magnification factor can be easily tuned by exploiting the direct dependence of the time-lens chirp with the peak power of a parabolic pump pulse. In a proof-of-concept experiment, T-to-F conversion and temporal magnification of picosecond optical waveforms are demonstrated using a fiber-optics scheme, where the T-to-F conversion and magnification factors are effectively tuned over a twofold range by controlling the gain of an optical amplifier. The same system can be additionally adjusted to provide a time-mapped Fourier transform of the input waveform.

Ultrafast electrical spectrum analyzer based on all-optical Fourier transform and temporal magnification.

Real-time electrical spectrum analysis is of great significance for applications involving radio astronomy and electronic warfare, e.g. the dynamic spectrum monitoring of outer space signal, and the instantaneous capture of frequency from other electronic systems. However, conventional electrical spectrum analyzer (ESA) has limited operation speed and observation bandwidth due to the electronic bottleneck. Therefore, a variety of photonics-assisted methods have been extensively explored due to the bandwidth advantage of the optical domain. Alternatively, we proposed and experimentally demonstrated an ultrafast ESA based on all-optical Fourier transform and temporal magnification in this paper. The radio-frequency (RF) signal under test is temporally multiplexed to the spectrum of an ultrashort pulse, thus the frequency information is converted to the time axis. Moreover, since the bandwidth of this ultrashort pulse is far beyond that of the state-of-the-art photo-detector, a temporal magnification system is applied to stretch the time axis, and capture the RF spectrum with 1-GHz resolution. The observation bandwidth of this ultrafast ESA is over 20 GHz, limited by that of the electro-optic modulator. Since all the signal processing is in the optical domain, the acquisition frame rate can be as high as 50 MHz. This ultrafast ESA scheme can be further improved with better dispersive engineering, and is promising for some ultrafast spectral information acquisition applications.

Characterization of ultrashort pulses by time-frequency conversion and temporal magnification based on four-wave mixing at 1 μm.

In order to characterize ultrashort pulses in real time at 1 μm wavelength, a temporal imaging structure based on the four-wave mixing effect in highly nonlinear fibers is implemented and analyzed both theoretically and experimentally. It is found that both time-frequency transfer and the temporal magnification process can be realized approximately in one structure. The pulse widths of the signal laser measured by the time-frequency transfer and the temporal magnification process are 3.2 ps and 3.1 ps, respectively, which are nearly the same and are in agreement with the result of the autocorrelator. The temporal magnification factor is 33, and the temporal resolution is 380 fs. The method based on the temporal magnification process is inherently real time and single shot, which makes it suitable for applications in the measurement of high-power ultrashort pulses. The four-wave mixing time lens promises future applications in the characterization of the single-shot high-power short laser.