Konstantin L. Vodopyanov

Full characterization of electric-field waveforms in amplitude and phase is achieved across the terahertz to visible spectral range through interaction with an optical pulse shorter than a half-cycle period via the Pockels (linear electro-optic) effect. This technique of electro-optic sampling has become an indispensable tool in various areas, including ultrafast pump-probe, time-domain and frequency-comb spectroscopies, quantum optics, high-harmonic generation, and attosecond science, and holds great promise for further advances. Not only does it enable spectroscopic measurements with record dynamic range and temporal resolution, along with massively parallel real-time spectral data acquisition, but its remarkable sensitivity also allows the detection of vacuum fluctuations, i.e., “zero-point motion” of electric fields, profoundly impacting our understanding of the fundamental laws of nature.

We present high-resolution dual-comb spectroscopy across two broad UV spectral regions spanning 372–410 nm and 325–342 nm. This is achieved by generating sixth and seventh harmonics, respectively, from a low-noise 2.35 µm Cr:ZnS dual-comb laser system. The sixth harmonic band contains approximately 1,000,000 spectrally resolved comb lines, while the seventh harmonic band—around 550,000 comb lines. With the line spacing of 80 MHz, this corresponds to a resolving power of up to 10 million, offering remarkable spectral resolution.

We have demonstrated high resolution dual comb spectroscopy in two wide UV bands: 325-342 nm and 372-410 nm based on high harmonic generation of a low-noise 2.35-μm Cr:ZnS dual comb laser system (the 7th and the 6th harmonics respectively). The bands consist of ~550,000 spectrally resolved comb modes for the 7th harmonics, and ~1,000,000 modes for the 6th harmonics with 80 MHz mode separation.

We have demonstrated high resolution dual comb spectroscopy in two wide UV bands: 325-342 nm and 372-410 nm based on high harmonic generation of a low-noise 2.35-μm Cr:ZnS dual comb laser system (the 7th and the 6th harmonics respectively). The bands consist of ~550,000 spectrally resolved comb modes for the 7th harmonics, and ~1,000,000 modes for the 6th harmonics with 80 MHz mode separation.

We perform dual-comb spectroscopy in two UV bands: 325-342 nm and 372-410 nm, corresponding to the 7th and 6th harmonics of a dual-comb 2.35-μm laser source, and simultaneously resolve ~500,000 and ~1,000,000 comb lines spaced by 80 MHz respectively.

Detecting the electric-field waveform of an optical pulse from the terahertz to the visible spectral domain provides a complete characterization of the average field waveform and holds great potential for quantum optics, time-domain (including frequency-comb) spectroscopy, high-harmonic generation, and attosecond science, to name a few. The field-resolved measurements can be performed using electro-optic sampling, where a laser pulse is characterized through an interaction with another pulse of a much shorter duration. The measured pulse train must consist of identical pulses, including their equal carrier-envelope phase (CEP). Due to the limited coverage of broadband laser gain media, creating CEP-stable pulse trains in the mid-infrared typically requires nonlinear frequency conversion, such as difference frequency generation, optical parametric amplification, or optical rectification. These techniques operate in a single-pass geometry, often limiting efficiency. In this work, we demonstrate field-resolved analysis of the pulses generated in a resonant system, an optical parametric oscillator (OPO). Due to the inherent feedback, this device exhibits a relatively high conversion efficiency at a given level of input power. By electro-optic sampling, we prove that a subharmonic OPO pumped with CEP-stable few-cycle fiber-laser pulses generates a CEP-stable mid-infrared output. The full amplitude and phase information renders dispersion control straightforward. We also confirm the existence of an exotic “flipping” state of the OPO directly in the time domain, where the electric field of consecutive pulses has the opposite sign.

Optical materials transparent in the CO₂ laser wavelength range have been evaluated regarding their suitability for components in ultrashort-pulse (≤ a few ps), high-peak-power (≥ a few TW) long-wave infrared (LWIR) lasers. We provide values for the nonlinear refractive index (n₂) for seventeen materials, and onsets for nonlinear absorption for eleven materials. Characterizations were performed using a 2 ps laser pulse at λ=9.2μm. This paper methodically presents the newly acquired data in conjunction with existing literature on linear optical properties, establishing it as a comprehensive reference for designing high-peak-power LWIR laser systems.

Starting from two phase-locked frequency combs based on Kerr-lens mode-locked Cr:ZnS lasers (2.35µm), we use various up- and down-conversion strategies to perform dual-comb spectroscopy across 1THz–1PHz range with up to some 1,000,000 comb-teeth resolved.

Ultrabroadband electro-optic sampling using few-optical-cycle probing pulses is a sensitive technique to detect electric field amplitudes with a high dynamic range and up to near-infrared optical frequencies. By combining this method with dual-frequency-comb spectroscopy and using a new class of ultrafast lasers, we perform high-resolution, 80 MHz/0.0027 cm−1 (10 MHz/0.0003 cm−1 with spectral interleaving), spectroscopic measurements in the frequency range 1.5–45 THz (6.6–200 µm), excluding the strongly absorbing Reststrahlen band of lattice resonances at 4.5–9 THz, with an instantaneous spectral coverage exceeding an octave (e.g., 9–22 μm). As a driving source, we use a pair of mutually coherent combs from Kerr-lens mode-locked solid-state Cr:ZnS (2.35 μm) lasers. One of the combs is frequency downconverted via intrapulse difference frequency generation to produce a longwave “sensing” comb, while the second comb is frequency doubled to produce a near-IR “probe” comb for electro-optic sampling (EOS). The low intensity and phase noise of our dual-comb system allow for capturing a large amount of spectral information (200 000 comb-mode-resolved spectral lines spaced by 80 MHz) in the mid-IR portion of the spectrum at a video rate of 69 Hz, with the signal-to-noise ratio limited by the shot noise of the near-IR EOS balanced detection system. Our dual-comb spectroscopy measurements with low-pressure gaseous ethanol, isoprene, and dimethyl sulfide reveal Doppler-limited spectroscopic signatures that have never been explored before.