A. N. Olenin

CARS diagnostics of molecular media under nanoporous confinement

The CARS spectroscopy is used for the diagnostics of carbon dioxide in a nanoporous glass at temperatures ranging from room temperature (20.5°C) to the subcritical temperature (30.5°C) in the pressure range below the saturated-vapor pressure. The contributions of the gas-phase molecules, the molecular layer adsorbed from the gas phase on the pore surface, the condensed liquid-like phase, and the liquid interface in the vicinity of the pore surface can be selected using the analysis of the nonlinear spectral response. The spectral behavior of the carbon dioxide confined in nanopores at the subcritical temperature indicates a state that is similar to the supercritical fluid. This corresponds to a low-temperature shift of the critical point of the medium confined in nanopores.

High resolution study of 1388 cm-1 CO2 vibration by time-domain CARS: spectral exchange and Dicke effect

Abstract The dephasing kinetics of the higher frequency component of the Fermi-resonance dyad ν 1 /2ν 2 (1388 cm −1 ) of CO 2 was studied by means of time-domain CARS in the density range where spectral exchange and Dicke effect play a noticeable role. The spectral exchange manifests itself in the gradual shift to longer delay times of minima and maxima of the beats between different Q -branch components with increasing densities and in the simultaneous beats smoothing. As a result of both the effects, the pulse response was practically exponential at CO 2 densities ⩾ 0.4 Amagat.

Broadening of vibrational spectra of carbon dioxide upon absorption and condensation in nanopores

Coherent anti-Stokes Raman Spectroscopy (CARS) has been used to study the vibrational Q-branch with the frequency of 1388 cm−1 of the ν1 mode of carbon dioxide molecules filling a sample made of nanopore glass at room temperature (20.5°C). The measurements were carried out in a gas cell at pressures approaching saturation Psat. When pressure was increased above 0.8 Psat, in addition to the spectral component due to the gaseous phase molecules, the CARS spectra featured a component due to the molecules adsorbed on the pore walls. Simulation of spectra taking the interference of these two contributions into account enabled the estimation of the broadening of the vibrational molecular spectra in the adsorbed layer. The spectral width of the component due to the adsorbed molecules was nearly a factor of two times larger than that of molecules in the bulk liquid phase. At pressures above 0.94 Psat, the spectral width of the component due to the adsorbed molecules decreased to values close to those measured in the bulk liquid phase, which corresponds to the condensation of molecules in nanopores.

Induction-resonance energy transfer between the terbium-binding peptide and the red fluorescent proteins DsRed2 and TagRFP

Two novel FRET-pairs: Tb3+-binding peptide-DsRed2 and Tb3+-binding peptide-TagRFP have been produced based on the terbium-binding peptide and the red fluorescent proteins DsRed2 and TagRFP. Two induction-resonance energy transfer processes in both FRET-pairs have been registered, from tryptophan of the terbium-binding peptide to Tb3+ and from sensitized Tb3+ to the acceptor, the chromophore, DsRed2 or TagRFP. The lifetimes of terbium in the presence and absence of the acceptor have been determined. It has been shown that the lifetime of Tb3+ in the presence of 150 mM NaCl decreases in both FRET-pairs. The efficiency of fluorescent resonance transfer from Tb3+ to the acceptor proteins is 28 and 35% for Tb3+-binding peptide-DsRed2 and Tb3+-binding peptide-TagRFP, respectively.

Spectral Characteristics of Subcritical Carbon Dioxide in Nanopores

Coherent anti-Stokes Raman scattering spectra measured within the Q-branch of the vibrational transition ν1 are used to gain insights into the state of carbon dioxide molecules in nanopores of Vycor™ glass at room temperature (20.5°C) and a subcritical temperature of 30.5°C and gas pressures up to the saturation point Psat for each temperature. Along with the main spectral component, belonging to gaseous CO2 molecules, the spectra recorded at pressures close to Psat feature a second (low-frequency) component. The second component is associated with the contribution from the CO2 molecules trapped inside pores. A spectral deconvolution with account for the interference of these two bands makes it possible to estimate the spectral characteristics of the second (low-frequency) component at each temperature. At 20.5°C, the bandwidth of the low-frequency component decreases with CO2 pressure, a behavior that can be explained by the transition of CO2 from the adsorbed to the condensed state in the pore. At the subcritical temperature of 30.5°C, the spectral width of the second component is pressure-independent and close to the value measured in the bulk of the supercritical fluid, a result likely associated with a low-temperature shift of the critical point of the substance trapped in nanopores.

Optical nutation at a Raman-active transition

Optical nutation at the Raman-active transition 6P1/2−6P3/2 of thallium atoms (ωR/2πc=7793 cm −1) under resonant Raman excitation by a biharmonic picosecond pulsed field, giving rise to substantial motion of the population, is detected. Optical nutation appears as an oscillatory behavior of the energy of the anti-Stokes scattering of probe pulses, which follow with a fixed delay, as a function of the product of the energies of the excitation pulses. As a result of the dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation conditions are satisfied for negative initial detunings of the Raman excitation frequency from resonance. The Raman scattering cross section for the transition under study is estimated by comparing the experimental data with the calculations.

Transformation of strong picosecond pulses in radiation with an extended quasirotational spectrum during self-focusing in high-pressure hydrogen

Radiation with a spectrum representing a discrete analog of the extended spectrum observed in the generation of a supercontinuum in gases is generated in the self-focusing of 30-ps pulses with a wavelength of 1.06 μ]m in hydrogen at pressures up to 120 atm. The spectrum contains lines with similar intensities, an average frequency spacing approximately equal to the rotational transition frequency in hydrogen (587 cm−1), and a smooth spatial profile. The lines consist of several vibrational-rotational components. As the pressure is increased, the spectral lines are transformed so that at a pressure above 60 atm each line in the spectrum contains one or two components formed as a result of the smaller number of cascade (rotational and vibrational) processes. Self-focusing is manifested in the occurrence of a radiating channel up to 12 cm in length. The formation of a channel of this length is associated mainly with the variation of the refractive index in vibrational excitation of the hydrogen molecules by electrons heated in the pump field.

Parametric amplification of broadband radiation of a cw superluminescent diode under picosecond pumping

It is proposed to use cw superluminescent diodes with a spectral width of about 300 and high spatial coherence as seed radiation sources in parametric amplifiers with picosecond pumping in order to form broadband picosecond pulses. A two-cascade parametric amplifier based on (BBO) crystals is pumped by pulses of the second harmonic of an Nd : YAG laser. For a superluminescent diode spectral width of (centre wavelength ), the spectral width of picosecond pulses at the parametric amplifier output is . At a total pump energy of for BBO crystals, the energy of the enhanced emission of the superluminescent diode is found to be .

Precise synchronization of qcw pumped active-passive mode locked picosecond lasers

We present designing qcw diode pumped Nd:YAG picosecond laser with 50 ps jitter of output pulse relative to active mode locking signal. Adjustment of signal delay in negative feedback circuit provides generation of transform-limited laser pulses. Obtained level of jitter is mainly attributed to phase noise of radio-frequency active mode locking signal generator. Further jitter decrease by means of enhancement of radio-frequency signal filtering and suppressing of phase noise is discussed.

Thermolens manifestation in end-pumped picosecond Nd:YAG laser

Experimental and theoretical modeling results for pulsed diode-array end-pumped Nd:YAG laser with aberrational thermolens are presented. Millijoule level energy stable picosecond pulse generation is realized in a wide range of repetition rates. Limiting factors of stable laser operation and quantitative contribution of aberrations in beam quality degradation are discussed.