Pulse Compression Scheme Research Articles

Robust design of mismatched filters in echo truncation for inter‐pulse waveform diversity radar

AbstractRange sidelobe modulation is a primary issue that forbids application of inter‐pulse and intra‐coherent processing interval (coherent processing interval) waveform diversity in moving target indication or moving target detection radars. Previous research has adopted mismatched filters (MMFs) to reconstruct identical compressed outputs based on an ideal model. In practice however, echo truncation is inevitable due to transceiver isolation, significantly degrading the effectiveness of MMFs. In this paper, the design of MMFs under an echo‐truncated model to achieve a robust design is considered. Specifically, the authors extract the dominant scattering profile from the close‐range echo and incorporate it into the MMF design model. To judiciously combine the robust design with the ideal one, a segmented pulse compression scheme is proposed. Numerical results indicate that the proposed robust processing scheme can effectively reduce clutter leakage in both truncated and intact scenarios.

Nonlinear pulse compression technique based on in multi-pass plano-cancave cavity

<sec>Ultrafast femtosecond laser system with hundreds of microjoules of energy, operating at a repetition frequency of several kilohertz, has very important applications in many fields such as medicine, mid-infrared laser generation, industrial processing, and vibrational spectroscopy. The chirped pulse amplification technique provides a feasible path to obtain light sources with those parameters. However, the use of chirped pulse amplification increases the technical complexity and cost of the laser system. Recently, the proposal of a multi-pass cell (MPC) nonlinear pulse compression technique has enabled us to obtain high power ultrafast femtosecond pulses with reduced technical complexity and cost. The device requires only two concave mirrors and a nonlinear medium in between. In the past seven years, the multi-pass cell nonlinear pulse compression technique has made great progress, making it possible to obtain ultrashort pulses with average power of more than a few kW and peak power of tens to hundreds of TW.</sec><sec>In this work, we achieve nonlinear pulse compression of a 100-W picosecond laser by using an improved nonlinear pulse compression scheme that combines a hybrid of a plano-cancave multi-pass cell and multi-thin-plate. Using fused silica plates in plano-cancave cavity, the spectral bandwidth (FWHM) of input picosecond laser is broadened from 0.24 nm to 4.8 nm due to self-phase modulation effect, the pulse is compressed to 483 fs by dispersion compensation using grating pairs, which corresponds to a compression factor of 22, and the final output power of 44.2 W is obtained. Compared with traditional MPC, the plano-cancave cavity scheme we developed is a very promising solution for nonlinear compression due to its compactness, more stability and large compression ratio.</sec>

Femtosecond Autocorrelation of Localized Surface Plasmons.

Plasmon electronic dephasing lifetime is one of the most important characteristics of localized surface plasmons, which is crucial both for understanding the related photophysics and for their applications in photonic and optoelectronic devices. This lifetime is generally shorter than 100 fs and measured using the femtosecond pump-probe technique, which requires femtosecond laser amplifiers delivering pulses with a duration even as short as 10 fs. This implies a large-scale laser system with complicated pulse compression schemes, introducing high-cost and technological challenges. Meanwhile, the strong optical pulse from an amplifier induces more thermal-related effects, disturbing the precise resolution of the pure electronic dephasing lifetime. In this work, we use a simple autocorrelator design and integrate it with the sample of plasmonic nanostructures, where a femtosecond laser oscillator supplies the incident pulses for autocorrelation measurements. Thus, the measured autocorrelation trace carries the optical modulation on the incident pulses. The dephasing lifetime can be thus determined by a comparison between the theoretical fittings to the autocorrelation traces with and without the plasmonic modulation. The measured timescale for the autocorrelation modulation is an indirect determination of the plasmonic dephasing lifetime. This supplies a simple, rapid, and low-cost method for quantitative characterization of the ultrafast optical response of localized surface plasmons.

Ideal spatio-temporal pulse distribution for exawatt-scale lasers based on simultaneous chirped beam and chirped pulse amplification.

This paper presents the ideal spatio-temporal pulse structure that is required to produce exawatt-scale pulses based on simultaneous chirped beam and chirped pulse amplification in a Nd:Mixed-glass laser system. It is shown, that a 100 fs Fourier transform-limited pulse is created from a 20 ns duration stretched beam-pulse after propagating through an appropriate six-grating compressor arrangement. Quantitative results, from a ray-tracing model of the six-grating compressor, provide the detailed spatio-spectral and spatio-temporal pulse distributions of the stretched pulse along with the higher-order phase distortions compensated by this pulse compression scheme.

Developments of Picosecond Lasers Based on Stimulated Brillouin Scattering Pulse Compression

Pulse compression based on stimulated Brillouin scattering (SBS) is a nonlinear optical approach that efficiently converts high-energy nanosecond pulses into the picosecond. Since the first observation of SBS pulse compression, different compression structures for different input and output parameters were developed to optimize the characteristics of pulse compression in the past decades. Here, a comprehensive review of the development status of SBS pulse compression schemes is provided, meanwhile, methods and trends to the optimization of SBS pulse compression are proposed.

Generation and compression of 10-fs deep ultraviolet pulses at high repetition rate using standard optics.

The generation and characterization of ultrashort laser pulses in the deep ultraviolet spectral region is challenging, especially at high pulse repetition rates and low pulse energies. Here, we combine achromatic second harmonic generation and adaptive pulse compression for the efficient generation of sub-10 fs deep ultraviolet laser pulses at a laser repetition rate of 200 kHz. Furthermore, we simplify the pulse compression scheme and reach pulse durations of ≈10 fs without the use of adaptive optics. We demonstrate straight-forward tuning from 250 to 320 nm, broad pulse spectra of up to 63 nm width, excellent stability and a high robustness against misalignment. These features make the approach appealing for numerous spectroscopy and imaging applications.

Enhanced Pulse Compression within Sign-Alternating Dispersion Waveguides

We show theoretically and numerically how to optimize sign-alternating dispersion waveguides for maximum nonlinear pulse compression, while leveraging the substantial increase in bandwidth-to-input peak power advantage of these structures. We find that the spectral phase can converge to a parabolic profile independent of uncompensated higher-order dispersion. The combination of an easy to compress phase spectrum, with low input power requirements, then makes sign-alternating dispersion a scheme for high-quality nonlinear pulse compression that does not require high powered lasers, which is beneficial for instance in integrated photonic circuits. We also show a new nonlinear compression regime and soliton shaping dynamic only seen in sign-alternating dispersion waveguides. Through an example SiN-based integrated waveguide, we show that the dynamic enables the attainment of compression to two optical cycles at a pulse energy of 100 pJ which surpasses the compression achieved using similar parameters for a current state-of-the-art SiN system.

Bulk, cascaded pulse compression scheme and its application to spin emitter characterization

The 35-fs-long pulses of a commercial Ti:sapphire amplifier are compressed to ∼20fs via self-phase modulation in bulk glass substrates. The cascading of both nonlinear broadening and dispersion compensation stages makes use of the increasing peak power in the successive nonlinear stages. As an application example, the compressed pulses are used for electro-optical sampling of terahertz waves created by optically pumped thin-film spin emitters.

A Compact, High-Gain, High-Power, Ultrawideband Microwave Pulse Compressor Using Time-Reversal Techniques

Generation of high-peak-power, microwave ultrashort pulses (USPs) is desirable for ultrawideband communications and radar/remote sensing. A variety of microwave USP generators exist today, or are described in the literature, and have benefits and limitations depending on the application. A new class of pulse compressors for generating USPs using electromagnetic time-reversal (TR) techniques has been developed in the last decade and is the topic of this article. This article presents a compact TR microwave pulse-compression cavity that has ultrawide bandwidth (BW) (5-18 GHz) and employs waveguide feeds for high-peak-power output over the entire band. The system uses a time-reversal-based pulse compression scheme with one-bit processing (OBTR) to achieve high-peak power. We present results from full-wave simulations and measurements showing compression gain exceeding 21.2 dB, 22% efficiency, and measured instantaneous peak output powers reaching 39.2 kW. These are all record results for this type of pulse compressor. In addition, we present a new analysis of variation in compression gain due to impulse response recording time and BW variation, new experimental work on the effect of mode stirrer position on compression gain, and a novel RF switch-based technique for reducing time-sidelobes while using OBTR.

Kagome-fiber prism compressor combination for Yb:KGW laser pulse compression to sub-40 fs

Spectral broadening in hollow-core fibers is an important tool for pulse compression of low-peak power laser pulses, especially for Yb-based lasers. Here, we present a pulse compression scheme to reduce the pulse duration of a commercial Yb:KGW laser operating at 100 kHz repetition rate and 40 μJ pulse energy from 390 to 38 fs. The spectral broadening is accomplished using a krypton-filled Kagome-type fiber. We report broadened spectra for variable Kr-pressures and input powers. At optimal settings of 8 bar Kr-pressure and 3.3 W input power, the bandwidth of the pulse at the −10 dB level increased from 9.5 to 85 nm corresponding to a Fourier limit of 26 fs. A simple SF10 prism compressor is used to reduce the accumulated chirp and shortens the fiber output from about 500 to 38 fs. In addition to the spectral broadening, a pressure dependent change of the polarization is observed.

Generation of High-Voltage Pulses with a Picosecond Front in a Cascade Kivotron Connection

The possibility of the operation of high-current high-voltage switches based on “open” discharge with the generation of counter-propagating electron beams, that is, kivotrons, in a two-stage pulse compression scheme is demonstrated experimentally. The total degree of the initial-pulse compression, which exceeded 600 at a minimum measured front duration of a generated pulse of at most 100 ps, was achieved at a voltage of up to 18 kV and a pulse-repetition rate of 1 kHz.

A fully integrated W‐band pulse compression radar CMOS transceiver

AbstractA fully integrated ultra‐wideband (UWB) W‐band pulse compression radar transceiver in a 65‐nm CMOS technology is presented. The transceiver adopts a pulse compression scheme for high power spectral density with low TX leakage. Two identical voltage controlled oscillators, which are coupled through the second harmonic, are designed to achieve high output power and low phase noise without buffers. A transformer‐based local oscillator distribution network is proposed to achieve both small chip area and high port‐to‐port isolation. The transceiver chip produces 7.5‐GHz UWB RF pulses with 14.5‐dBm peak output power in the tuning range of 75–81 GHz, while the receiver shows a dynamic range of above 60 dB. The radar module was realized with waveguide transitions from a micro‐strip to a WR‐10 waveguide, and was capable of differentiating two targets with 6.5‐cm separation within 30 m distance.

Efficient High-Power Ultrashort Pulse Compression in Self-Defocusing Bulk Media

Peak and average power scalability is the key feature of advancing femtosecond laser technology. Today, near-infrared light sources are capable of providing hundreds of Watts of average power. These sources, however, scarcely deliver pulses shorter than 100 fs which are, for instance, highly beneficial for frequency conversion to the extreme ultraviolet or to the mid- infrared. Therefore, the development of power scalable pulse compression schemes is still an ongoing quest. This article presents the compression of 90 W average power, 190 fs pulses to 70 W, 30 fs. An increase in peak power from 18 MW to 60 MW is achieved. The compression scheme is based on cascaded phase-mismatched quadratic nonlinearities in BBO crystals. In addition to the experimental results, simulations are presented which compare spatially resolved spectra of pulses spectrally broadened in self-focusing and self-defocusing media, respectively. It is demonstrated that balancing self- defocusing and Gaussian beam convergence results in an efficient, power-scalable spectral broadening mechanism in bulk material.

Nonlinear pulse compression in a multi-pass cell.

We demonstrate a scheme for nonlinear pulse compression at high average powers based on self-phase modulation in a multi-pass cell using fused silica as the nonlinear medium. The scheme is suitable for compression of pulses with peak powers exceeding the threshold for critical self-focusing. At >400 W of input power, the pulses of a Yb:YAG-Innoslab laser system (10MHz repetition rate, 850fs pulse duration) are spectrally broadened from 1.6 to >13.5 nm bandwidth while maintaining almost diffraction-limited beam quality. The chirp is removed with a dispersive mirror compressor, and pulse durations of 170fs at an output power of 375W are achieved. The compression unit reaches an overall transmission of >90%.

Single laser pulse compression via strongly coupled stimulated Brillouin scattering in plasma

Laser amplification in plasma, including stimulated Raman scattering amplification and strongly coupled stimulated Brillouin scattering (sc-SBS) amplification, is very promising to generate ultrahigh-power and ultrashort laser pulses. But both are quite complex in experiments: at least three different laser pulses must be prepared; temporal delay and spatial overlap of these three pulses are difficult. We propose a single pulse compression scheme based on sc-SBS in plasma. Only one moderately long laser is applied, the front part of which ionizes the gas to produced plasma, and gets reflected by a plasma mirror at the end of the gas channel. The reflected front quickly depletes the remaining part of the laser by sc-SBS in the self-similar regime. The output laser is much stronger and shorter. This scheme is at first considered theoretically, then validated by using 1D PIC simulations.

High-quality pulse compression in a novel architecture based on a single-mode fiber cascading a nonlinear optical loop mirror

A novel all-fiber low-pedestal pulse compression scheme is proposed and investigated. The scheme is based on an anomalously dispersive single-mode fiber (SMF) cascading a nonlinear optical loop mirror (NOLM) with another anomalously dispersive SMF in the loop. Numerical results show that excellent pulse compression and pedestal reduction can be achieved by using the proposed scheme.

High Degree Picosecond Pulse Compression in Chalcogenide-Silicon Slot Waveguide Taper

In this paper, we propose and design a chalcogenide (As2S3)-based slot waveguide taper with exponentially decreasing dispersion profile to realize high-degree pulse compression of low-power chirped solitons. Based on the waveguide taper designed, pulse compression of fundamental solitons, and chirped 2-soliton breather are both investigated numerically. With self-similar pulse compression scheme, a 1 ps input pulse is compressed to 81.5 fs in 6 cm propagation. By using 2-soliton breather pulses, a 1 ps chirped pulse is compressed to 80.3 fs in just 2.54 cm. This is the first demonstration of the feasibility of high-degree nonlinear pulse compression in As2S3-based slot waveguide taper.

Generation of spectrally stable 6.5-fs visible pulses via filamentation in krypton

We produced $5\text{-}{\rm\mu}\text{J}$ , 6.5-fs visible pulses at a repetition rate of 1 kHz using filamentation in a gas cell filled with krypton followed by spectral selection and phase compensation by a combination of dielectric mirrors. The visible pulses have a smooth spectrum from 520 to 650 nm with a shot-to-shot stability in each spectral component of better than 2% (standard deviation). This pulse compression scheme is simple and robust, and can be easily integrated into intense ultrashort-pulse laser systems.

Concept for Pulse Compression Device Using Structured Spatial Energy Distribution

We explore a novel concept for pulse compression scheme applicable at RF, microwave, and possibly up to optical frequencies based on structured energy distribution in cavities supporting degenerate band-edge (DBE) modes. We show the high spatial concentration of energy due to DBE modes and proper choice of boundary conditions in coupled transmission lines (TLs) provide the basis for superior performance of the structured cavity when compared to a conventional cavity. We investigate the novel cavity features: larger loaded quality factor of the cavity and stored energy compared to conventional designs, robustness to variations of cavity loading, energy feeding and extraction at the cavity center, and substantial reduction of the cavity size by use of equivalent lumped circuits for low-energy sections of the cavity. Structured energy also allows for controlled pulse shaping via engineered extraction techniques. The presented concepts are general, in terms of equivalent coupled TLs, and can be applied to a variety of realistic guiding structures. Potential applications include microwave pulse compression devices, on-chip millimeter-wave pulse generation, and pulsed laser generation.

A W-Band 4-GHz Bandwidth Phase-Modulated Pulse Compression Radar Transmitter in 65-nm CMOS

This paper presents a fully integrated W-band 4-GHz bandwidth (BW) pseudo-noise (PN)-coded pulse compression radar transmitter (TX) in a CMOS technology. The PN-coded pulse compression scheme is adopted to obtain high spectral density and to lower the TX leakage using a 63-bit PN code generator based on linear feedback shift registers. We propose a sub-harmonic pumped pulse former and a pulsed power amplifier for high TX efficiency with the suppression of local oscillator (LO)/2LO leakage. A frequency synthesizer including a frequency divider chain generates a sub-harmonic LO signal, as well as a 5-GHz digital clock. Digital blocks with the PN-code generator are synchronized with the clock signal, which makes all pulses start with the same phase. The proposed TX achieves 14.5-dBm maximum output power with the tuning range of 75–81.5 GHz, and the phase noise is ${-}{\hbox{95.2}}$ dBc/Hz at a 1-MHz offset in the range of LO frequencies. In pulse mode, it generates a 4-GHz BW RF pulse signal, which corresponds to a range resolution of 7.5 cm, and the average dc power dissipation is 160 mW.