Multi-microjoule GaSe-based mid-infrared optical parametric amplifier with an ultra-broad idler spectrum covering 4.2-16 {\mu}m

We report a multi-microjoule, ultra-broadband mid-infrared optical parametric amplifier based on a GaSe nonlinear crystal pumped at ~2 {\mu}m. The generated idler pulse has a flat spectrum spanning from 4.5 to 13.3 {\mu}m at -3 dB and 4.2 to 16 {\mu}m in the full spectral range, with a central wavelength of 8.8 {\mu}m. The proposed scheme supports a sub-cycle Fourier-transform-limited pulse width. A (2+1)-dimensional numerical simulation is employed to reproduce the obtained idler spectrum. To our best knowledge, this is the broadest -3 dB spectrum ever obtained by optical parametric amplifiers in this spectral region. The idler pulse energy is ~3.4 {\mu}J with a conversion efficiency of ~2% from the ~2 {\mu}m pump to the idler pulse.Comment: 5 pages, 5 figure

Mid-infrared computational temporal ghost imaging

Ghost imaging in the time domain allows for reconstructing fast temporal objects using a slow photodetector. The technique involves correlating random or pre-programmed probing temporal intensity patterns with the integrated signal measured after modulation by the temporal object. However, the implementation of temporal ghost imaging necessitates ultrafast detectors or modulators for measuring or pre-programming the probing intensity patterns, which is not universally available in all spectral regions especially in the mid-infrared range. Here, we demonstrate a frequency downconversion temporal ghost imaging scheme that enables to extend the operation regime to arbitrary wavelengths regions where fast modulators and detectors are not available. The approach modulates a signal with temporal intensity patterns in the near-infrared and transfers the patterns to an idler via difference-frequency generation at the wavelength of the temporal object to be retrieved. As a proof-of-concept, we demonstrate temporal ghost imaging in the mid-infrared. The scheme is flexible and introduces new possibilities for scan-free pump-probe imaging and the study of ultrafast dynamics in spectral regions where ultrafast modulation or detection is challenging such as the mid-infrared and THz regions

High-energy mid-infrared sub-cycle pulse synthesis from a parametric amplifier

High-energy phase-stable sub-cycle mid-infrared pulses can provide unique opportunities to explore phase-sensitive strong-field light-matter interactions in atoms, molecules and solids. At the mid-infrared wavelength, the Keldysh parameter could be much smaller than unity even at relatively modest laser intensities, enabling the study of the strong-field sub-cycle electron dynamics in solids without damage. Here we report a high-energy sub-cycle pulse synthesiser based on a mid-infrared optical parametric amplifier and its application to high-harmonic generation in solids. The signal and idler combined spectrum spans from 2.5 to 9.0 μm. We coherently synthesise the passively carrier-envelope phase-stable signal and idler pulses to generate 33 μJ, 0.88-cycle, multi-gigawatt pulses centred at ~4.2 μm, which is further energy scalable. The mid-infrared sub-cycle pulse is used for driving high-harmonic generation in thin silicon samples, producing harmonics up to ~19th order with a continuous spectral coverage due to the isolated emission by the sub-cycle driver

Low divergence single-mode surface-emitting concentric-circular-grating terahertz quantum cascade lasers

We report the design, fabrication and experimental characterization of surface-emitting terahertz (THz) frequency quantum cascade lasers (QCLs) with distributed feedback concentric-circular-gratings. Single-mode operation is achieved at 3.73 THz with a side-mode suppression ratio as high as ~30 dB. The device emits ~5 times the power of a ridge laser of similar dimensions, with little degradation in the maximum operation temperature. Two lobes are observed in the far-field emission pattern, each of which has a divergence angle as narrow as ~13.5° × 7°. We demonstrate that deformation of the device boundary, caused by anisotropic wet chemical etching is the cause of this double-lobed profile, rather than the expected ring-shaped pattern

Design and fabrication of ultraviolet metal-oxide light-emitting devices

Zinc Oxide (ZnO) has a wide bandgap energy (~3.37 eV) and high exciton binding enegy (~ 60 meV) which is more than two times larger than that of Gallium Nitride (GaN). Therefore, ZnO has been recognized as a promising candidate of ultraviolet (UV) optoelectronic devices operating at room temperature or even at high temperature. Especially, the high exciton binding energy favors the excitonic stimulated emission in the application of lasers. However, ZnO has a wurtzite crystal structure, and thus two sufficiently smooth mirror surfaces are hardly to be cleaved to form Fabry-Perot cavity. The discovery and development of ZnO random laser successfully avoid this difficulty by forming the lasing resonance via multi-scattering in a closed-loop feedback.DOCTOR OF PHILOSOPHY (EEE

A generalized analytical model of gain bandwidth for design of optical parametric amplifiers

An analytical model is derived for calculating the maximum gain bandwidth of optical parametric amplifiers (OPA). The model relates in an explicit but simple way the gain bandwidth to the key design parameters of an optical parametric amplifier. It can be used as a tool to obtain the design parameters of an OPA capable of achieving the maximal gain bandwidth. The model is especially useful to design of long wavelength (>6μm)optical parametric amplifiers which have small difference between the center wavelengths of pump and signal.Agency for Science, Technology and Research (A*STAR)We acknowledge the financial support from SERC, Singapore (Grant No. 1426500050, and 1426500051) from the Agency for Science, Technology and Research (A*STAR), Singapore

High-energy mid-infrared sub-cycle pulse synthesis

We present the carrier-envelope phase-stable mid-infrared sub-cycle pulses, synthesized from an optical parametric amplifier covering the 2.5-9.0 μm range. The strong-field applications in solids and nano-structures are discussed

High-energy mid-infrared intrapulse difference-frequency generation with 5.3% conversion efficiency driven at 3 µm

Intrapulse difference-frequency generation (IPDFG) is a relatively simple technique to produce few-cycle mid-infrared (MIR) radiations. The conversion efficiency of IPDFG could be potentially improved by using the long driving wavelength to reduce the quantum defect. In this paper, we report a high-energy MIR IPDFG source with a record-high conversion efficiency of up to 5.3%, driven by 3 µm, 35 fs, 10 kHz pulses. The IPDFG output has a 5 µJ pulse energy and 50 mW average power. It spans over a spectral range from 6 to 13.2 µm. A 68 fs of IPDFG pulse width is measured, corresponding to 2.1 cycles, centered at 9.7 µm. The high-energy, two-cycle IPDFG pulses are used to produce a 3-octave supercontinuum in a KRS-5 crystal, spanning from 2 to 16 µm, with a 2.4 µJ pulse energy and a 24 mW average power.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Published versionAgency for Science, Technology and Research (1426500050, 1426500051, A1890b0049); Ministry of Education - Singapore (MOE 2016-T2-1-128)