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A quartz-enhanced photoacoustic spectroscopy based gas sensor was optimized to improve its compact spectrophone design and performance. The impact of a 2-tube microresonator geometry on the detected signal and signal to noise ratio (SNR) was investigated. Experimental studies demonstrate that the l=4.4 mm long tubes (ID=0.5 mm) result in a significantly enhanced SNR.
We have used terahertz time-domain spectroscopy to investigate carrier dynamics in a wide range of semiconductors. The technique allows discriminating between free charges and excitons and is perfectly suitable to study carrier-carrier interactions in nanostructured materials.
Using wavelengths between 2.6 and 3.8 microns from a fiber-based supercontinuum laser, lipids and proteins can be identified and selectively ablated. Absorption spectroscopy and selective ablation are conducted on atherosclerotic plaque constituents and adipose/fat tissues.
We realized a continuous-wave terahertz spectrometer based on optical heterodyning of two near-infrared distributed-feedback diode lasers. Using active frequency stabilization we achieve 1 MHz resolution and a signal-to-noise ratio up to 80 dB.
The appearance of the two-photon strong-coupling states is analyzed in atomic vs. semi-conductor quantum-dot microcavities. An identical excitation mechanism explains phenomena observed in photon-correlation measurements.
We investigate exciton dynamics in disordered quantum wells with optical two-dimensional Fourier transform spectroscopy (2DFTS). The lack of cross peaks in 2DFTS suggests that excitons localized in spatially separated regions are uncoupled.
We demonstrate a simple experimental technique to perform optical Two-Dimensional Fourier Transform Spectroscopy. This technique derives from a modified pump-probe geometry with a pair of collinear, phase-locked pump pulses.
Two-quantum coherences in two-dimensional Fourier-transform (2DFT) spectra are attributed to many-body interactions. 2DFT spectroscopy allows two-quantum coherences in semiconductors to be isolated. As a result, many-body coherences can be separated from biexciton coherences.
It is shown that a wavelet power spectrum estimation technique can be applied to high-resolution terahertz time-domain spectroscopy using asynchronous optical sampling to effectively remove noises without sacrificing spectral features on a spectrum.
We have performed open-aperture Z-scan measurements on n-doped InGaAs using intense few-cycle terahertz pulses. We observe a significant bleaching of the terahertz pulse absorption attributed to terahertz-electric-field-induced intervalley carrier scattering.
We demonstrate high-resolution Fourier-transform terahertz spectroscopy using two terahertz frequency combs with stabilized different repetition frequencies without a mechanical time delay tool.
Optical spectra of InAs quantum dot molecules show clear signatures of 2-photon absorption through sequential and simultaneous transitions. Biexcitons can be spatially direct or indirect, producing 2-photon transitions that are unique to molecules.
We resolve complex electron autoionization dynamics in molecules in real time for the first time, where a second electron cannot be ejected from O2 until the internuclear separation of the fragments is >30 Aring.
An Yb-doped fiber laser and amplifier system is used together with an enhancement cavity for high harmonic generation for precision spectroscopy. Higher order harmonics can be produced in comparison to systems with Ti:sapphire lasers.
We present an externally and actively tuneable metamaterial composed of random subwavelength elements that is experimentally shown to alter the propagation direction of terahertz pulses by an amount adjustable via an external magnetic field.
We have identified 68 rotational transitions from three isotopic variants of nitrous oxide, among which 29 were never observed previously. By deducing and comparing the rotational constants, we have reliably differentiated among three isotopic variants.
We show a technique to measure the two-photon excitation spectrum of various fluorophores, based on Fourier transform nonlinear spectroscopy with the use of ultrabroadband laser (670-1100 nm).
Ethylene (C2H4) absorption line intensity at 6172.95 cm-1 was determined for trace gas detection. C2H4 trace concentration measurements were performed using quartz enhanced photoacoustic spectroscopy (QEPAS) with a sensitivity of 1.3 ppmv (1sigma) for tau=1s time constant. The effect of modulation frequency accuracy on QEPAS signal was investigated.
We have observed third-harmonic generation by single nanorods in solution and investigated its excitation polarization dependence. Our findings demonstrate the possibility of using third-harmonic signals for correlation spectroscopy, in contrast to conventional fluorescence correlation spectroscopy.
High-time-resolution broadband pump-probe spectroscopy of rhodopsin reveals the loss of reactant and appearance of photoproduct features within ap100 fs, which are signatures of a wavepacket moving through a conical intersection. Experiments are supported by molecular dynamics simulations.
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