Amplified bursts of laser pulses are sought for various machining, deposition, spectroscopic and strong-field applications. Standard frequency- and time-domain techniques for pulse division become inadequate when intraburst repetition rates reach the terahertz (THz) range as a consequence of inaccessible spectral resolution, requirement for interferometric stability, and collapse of the chirped pulse amplification (CPA) concept due to the loss of usable bandwidth needed for safe temporal stretching. Avoiding the burst amplification challenge and resorting to a lossy post-division of an isolated laser pulse after CPA leaves the limitations of frequency- and time-domain techniques unsolved. In this letter, we demonstrate an approach that successfully combines amplitude and phase shaping of THz bursts, formed using the Vernier effect, with active stabilization of spectral modes and efficient energy extraction from a CPA regenerative amplifier. As proof of concept, the amplified bursts of femtosecond near-infrared pulses are down-converted into tunable THz-frequency pulses via optical rectification.
Highly-efficient optical generation of narrowband terahertz (THz) radiation enables unexplored technologies and sciences from compact electron acceleration to charge manipulation in solids. State-of-the-art conversion efficiencies are currently achieved using difference-frequency generation (DFG) driven by temporal beating of chirped pulses but remain, however, far lower than desired or predicted. Here we show that high-order spectral phase fundamentally limits the efficiency of narrowband DFG using chirped-pulse beating and resolve this limitation by introducing a novel technique based on tun…
The development of multiplexing information transmission technology in the THz band may accelerate the arrival of the 6G era. In this paper, has demonstrated the feasibility of forming a sequence of subpulses in the temporal domain and the corresponding quasidiscrete spectrum in the THz frequency range. It is shown that despite the fact that the THz pulse has an exponential chirp, there is a "linkage relation" between spectrum and temporal structures of the THz pulse train. This fact can be used for encoding information in THz pulses for implementation in 6G communication systems in the future…
We demonstrate an efficient procedure for terahertz-wave radiation generation by applying a nonlinear wavelength conversion approach using a mid-infrared pump source. We used a 3.3 μm dual-chirped optical parametric amplification source and a 1.5 μm fiber laser for a comparison of energy conversion efficiencies. Nonlinear inorganic and organic crystals were used, and for the periodically-poled lithium niobate crystal, the efficiencies were 1.3*10^-4 and 5.6*10^-12 for the 3.3 μm source and the 1.5 μm source, respectively. We confirmed that nonlinear crystals could be pumped with tera-watt / cm…
We report multicycle, narrowband, terahertz radiation at 14.8 THz produced by phase-matched optical rectification of femtosecond laser pulses in bulk lithium niobate (LiNbO$_3$) crystals. Our experiment and simulation show that the output terahertz energy greatly enhances when the input laser pulse is highly chirped, contrary to a common optical rectification process. We find this abnormal behavior is attributed to a linear electro-optic (or Pockels) effect, in which the laser pulse propagating in LiNbO$_3$ is modulated by the terahertz field it produces, and this in turn drives optical rectif…
Pulse shaping is important for communications, spectroscopy, and other applications that require high peak power and pulsed operation, such as radar systems. Unfortunately, pulse shaping remains largely elusive for terahertz (THz) frequencies. To address this void, a comprehensive study on the dispersion tunability properties of THz chirped pulses traveling through a dielectric-lined hollow-core waveguide loaded with a helical graphene ribbon is presented.
High energy single- to few-cycle terahertz pulses enable the exploration of the frontier of science, such as electron acceleration, strong-field physics, and spectroscopy. One important method of generating such terahertz pulses is to use the tilted-pulse-front (TPF) technique. However, due to the non-collinear phase-matching, the large angular dispersion leads to a spatial and temporal break-up of the optical pump, limiting the terahertz generation efficiency and reducing the few-cycle character of the generated terahertz fields. To reduce the effects caused by angular dispersion, multiple sc…
We report a plasma-based strong THz source generated by using intense femtosecond laser pulses to irradiate solid targets at relativistic intensity >10^18W/cm2. Energies up to 50 microJ/sr per THz pulse is observed in the specular direction when the laser pulses are incident onto a copper foil at 67.5 degree. The source appears to be linearly polarized. The temporal, spectral properties of the THz are measured by a single shot, electro-optic sampling method with a chirped laser pulse. The THz radiation is attributed to the self-organized transient fast electron currents formed along the target…
By combining a tilted-pulse-intensity-front scheme using a LiNbO3 crystal and a chirped-pulse-beating method, we generated a narrowband intense terahertz (THz) pulse, which had a maximum electric field of more than 10 kV/cm at around 2 THz, a bandwidth of about 50 GHz,and frequency tunability from 0.5 to 2 THz. By performing THz-pump and near-infrared-probe experiments on GaAs quantum wells, we observed that the resonant excitation of the intraexcitonic 1s-2p transition induces a clear and large Autler-Townes splitting. Our time-resolved measurements show that the splitting energy observed in …
We present a high-power source of broadband terahertz radiation covering the whole THz spectral region (0.1-30 THz). The two-color gas plasma generation process is driven by a state-of-the-art Ytterbium fiber chirped pulse amplification system based on coherent combination of 16 rod-type amplifiers. Prior to the THz generation, the pulses are spectrally broadened in a multi-pass-cell and compressed to 37 fs with a pulse-energy of 1.3 mJ at a repetition rate of 500 kHz. A gas-jet scheme has been employed for the THz generation, increasing the efficiency of the process to 0.1%. The air-biased-co…
We present a near-infrared optical parametric chirped-pulse amplifier (OPCPA) and soft X-ray (SXR) high-harmonic generation system. The OPCPA produces few-cycle pulses at a center wavelength of 800 nm and operates at a high repetition rate of 100 kHz. It is seeded by fully programmable amplitude and phase controlled ultra-broadband pulses from a Ti:sapphire oscillator. The output from the OPCPA system was compressed to near-transform-limited 9.3-fs pulses. High-power operation up to an average power of 35 W was achieved, and a fully characterized pulse compression was recorded for a power leve…
We report on the group delay observed in continuous-wave terahertz spectroscopy based on photomixing with phase-sensitive homodyne detection. We discuss the different contributions of the experimental setup to the phase difference Δϕ(ν) between transmitter arm and receiver arm. A simple model based on three contributions yields a quantitative description of the overall behavior of Δϕ(ν). Firstly, the optical path-length difference gives rise to a term linear in frequency. Secondly, the ultra-wideband log-spiral antennae effectively radiate and receive in a frequency-dependent active region, wh…
In contrast with imaging using position-resolving cameras, single-pixel imaging uses a bucket detector along with spatially structured illumination for image recovery. This emerging imaging technique is a promising candidate for a broad range of applications due to high signal-to-noise ratio (SNR) and sensitivity, and applicability in a wide range of frequency bands. Here, inspired by single-pixel imaging in the spatial domain, we demonstrate a temporal single-pixel imaging (TSPI) system that covers frequency bands including both terahertz (THz) and near-infrared (NIR) region. By implementing …
