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1.
Opt Lett ; 48(9): 2273-2276, 2023 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-37126252

RESUMO

Using sub-3-cycle pulses from mode-locked Cr:ZnS lasers at λ ≈ 2.4 µm as a driving source, we performed high-resolution dual-frequency-comb spectroscopy in the longwave infrared (LWIR) range. A duo of highly coherent broadband (6.6-11.4 µm) frequency combs were produced via intrapulse difference frequency generation in zinc germanium phosphide (ZGP) crystals. Fast (up to 0.1 s per spectrum) acquisition of 240,000 comb-mode-resolved data points, spaced by 80 MHz and referenced to a Rb clock, was demonstrated, resulting in metrology grade molecular spectra of N2O (nitrous oxide) and CH3OH (methane). The key to high-speed massive spectral data acquisition was low intensity and phase noise of the LWIR combs and high (7.5%) downconversion efficiency, resulting in a LWIR power of 300 mW for each comb.

2.
Opt Express ; 27(11): 16405-16413, 2019 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-31163818

RESUMO

We report a technique for generation of broad and coherent femtosecond (fs) continua that span several octaves from visible to long-wave IR parts of the spectrum (0.4-18 µm). The approach is based on simultaneous amplification of few-cycle pulses at 2.5 µm central wavelength at 80 MHz repetition rate, and augmentation of their spectrum via three-wave mixing in a tandem arrangement of polycrystalline Cr:ZnS and single crystal GaSe. The obtained average power levels include several mW in the 0.4-0.8 µm visible, 0.23 W in the 0.8-2 µm near-IR, up to 4 W in the 2-3 µm IR, and about 17 mW in the 3-18 µm long-wave IR bands, respectively. High brightness and mutual coherence of all parts of the continuum was confirmed by direct detections of the carrier envelope offset frequency of the master oscillator.

3.
Opt Express ; 24(12): 12730-9, 2016 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-27410292

RESUMO

The new optical gating technique uses a femtosecond optical laser pulses for the photoconductive detection of short pulses of terahertz (THz) radiation. This technique reproduces the shape of the THz pulse and after pulse plasmonic response of the two-dimensional electron gas in a short channel high electron mobility transistor (HEMT). The results are in excellent agreement with the electro-optic effect measurements and with the simulation results obtained in the frame of a two-dimensional hydrodynamic model. The femtosecond optical laser pulse time is delayed with respect to the THz pulse and generates a large concentration of the electron-hole pairs in the AlGaAs/InGaAs HEMT. This drastically increases the channel conductivity on the femtosecond scale and effectively shorts the device quenching the transistor response. The achieved time resolution is better than 250 femtoseconds and could be improved using shorter femtosecond laser pulses. The spatial resolution of this technique is on the order of tens of nanometers or even smaller. It could be applied for studying the electron transport in a variety of electronic devices ranging from silicon MOSFETs to heterostructure bipolar transistors.

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