Spectroscopy Of Electronic Transitions Research Articles

Generation and research progress of femtosecond optical frequency combs in extreme ultraviolet

Femtosecond optical frequency combs have revolutionized the precision measurement of optical frequency and ultrafast science. Furthermore, the frequency combs expended to extreme ultraviolet (XUV) wavelength could provide an effective tool in attosecond pulse generation, nonlinear optics in ultraviolet, spectroscopy of electronic transitions and experiment of quantum electrodynamics. XUV femtosecond optical frequency combs need to be indirectly obtained by means of high-harmonic generation (HHG) drived by femtosecond pulses with high-repetition rate and extremely high peak power. In this review, firstly, the generation principle and the driving laser source requirements of femtosecond pulses generation in XUV spectral range are introduced. Basing on the requirements of driving laser sources, the several femtosecond laser amplification techniques are described, such as chirped pulse amplification (CPA), optical parametric chirped pulse amplification (OPCPA), double cladding pumped fiber amplifier and femtosecond enhancement cavity (fsEC). Meanwhile, the relative merits and applicability of which for XUV femtosecond optical frequency combs generation are compared. Secondly, in the HHG process, the XUV is generated collinearly or non-collinearly with the optical driving field. For the collinear generation process, one of the fundamental challenges is the design of a high-efficiency XUV output coupler. Here, three methods for out-coupling the XUV are expounded. Also, the theory of non-collinear XUV generation is mentioned. Finally, some typical research progress of XUV femtosecond optical frequency combs generation based on fsEC, OPCPA and femtosecond oscillators are reviewed respectively, as well as the current problems that need to be optimized are summarized.

Calculations of optical properties of some molecules suitable for coating of nanoparticles for biological applications

Coating of nanoparticles by various molecules is promising way to modify their surfaces and extend their bio-functionality, and infrared (IR), and spectroscopy of electronic transitions at ultraviolet and visible (UV/VIS) wavelengths are suitable techniques to investigate details of their attachment at nanoparticle surface. In the present work structure and optical properties of dextran, chitosan, oleic acid and poly(ethylene glycol) have been investigated by semi-empirical quantum mechanics, and ab initio Hartree–Fock calculations using the HyperChem® software package (http://www.hyper.com). The equilibrium conformations, IR, and UV/VIS spectra of molecules of various lengths, before and after their attachment to the magnetite (111) surface are determined, and IR modes and UV/VIS transitions that change the most upon the molecules attachment identified. The results are compared to the existing experimental data and the results of similar calculations, and possible implications for biological applications of nanoparticles coated with the investigated molecules have been discussed.

Low-energy electron-energy-loss spectroscopy of electronic transitions in solid carbon dioxide

We report electron-energy-loss spectra of solid films of CO2 for electronic transitions induced by 15, 19.4, and 25 eV incident electrons. All spectra were obtained under sufficiently small electron exposures so as to avoid sample damages. The use of a low-energy electron along with the backscattering geometry give access to spin- and symmetry-forbidden transitions while the effect of the condensed phase makes it possible to modify the energy, ordering, and magnitude of most gas-phase transitions. The most noticeable observation is the disappearance of all sharp energy-loss peaks attributed to a Rydberg series of CO2 in the gas phase. In contrast, transitions to the molecular valence Δu3,1 and Σu−3,1 states are located virtually at the same energy as in the gas phase. The strong dipole-allowed valence Σu+1 transition is found shifted to lower energy by about 0.3 eV while transitions to mixed Rydberg-valence Πg3,1 and Πu1 states are both shifted to higher energy by about 0.4–0.5 eV. The lowest valence Σu+3 transition is ascribed to the lowest energy-loss feature in the solid at 7.9 eV.

Transient polarization four-photon “non-Condon” spectroscopy of electronic transitions in complex molecules

We show both theoretically and experimentally that resonance transient grating spectroscopy (RTGS) is a good method for the investigation of ultrafast solvation dynamics of large probe molecules in solutions. We have studied the solvation dynamics of LDS 750 in many solvents in a broad time range by RTGS and by induced optical Kerr effect spectroscopy. We propose a new method for the investigation of non-Condon effects in solvation: transient polarization four-photon spectroscopy.

Excitation spectrum of a two-dimensional Wigner lattice.

We propose a spectroscopic method to determine the existence of an electronic Wigner lattice at a given electron density n. We derive the ``perpendicular'' excited states of the two-dimensional Wigner lattice on a dielectric layer with a metallic substrate, and compare them with the corresponding excited states of the two-dimensional electron gas at the same electron densities. The transitions from the ground to the first excited state are studied in detail and we have found a significant difference between the lattice and the gas excitation energies for n\ensuremath{\gtrsim}${10}^{8}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$. In that sense, the spectroscopy of electronic transitions can prove the existence of a Wigner lattice and a rapid change in the excitation spectrum can serve for determination of the lattice melting temperature. A linear Stark effect in the case of a Wigner lattice is also analyzed.

“Condon” and “non‐Condon” Nonlinear Spectroscopy of Polyatomic Molecules in Solutions: Solvation Dynamics Study

AbstractA theoretical basis for the solvation dynamics study of complex molecules in solutions by resonance four‐photon spectroscopy has been developed. A non‐Markovian theory of four‐photon spectroscopy of electronic transitions in complex molecules has been generalized for the “non‐Condon” tensor case. It has been shown that for definite conditions the cubic susceptibility χ(3), describing four‐photon interaction, can be expressed as a product of “Condon” and non‐Condon parts. The latter describes the mixing effect of different electronic molecular states by nuclear motions (Herzberg‐Teller effects). The Condon part depends on the excitation frequency, and the non‐Condon one depends on the polarization state of the pump and the probe beams. It has been shown that the Condon resonance transient grating spectroscopy is a good method for the investigation of ultrafast solvation dynamics.The dependence of the non‐Condon part of χ(3) on the polarizations of the interacting beams permits one to formulate the principles of a new method for the investigation of Herzberg‐Teller effects on electronic molecular transitions by transient polarization four‐photon spectroscopy.

Doppler-limited laser spectroscopy of electronic transitions in SnO

Laser-induced fluorescence with narrow-band excitation and time resolution has been used for the first time to investigate the quantum-resolved dynamics of excited states of 120SnO. Transitions to both the A1Π and b′3Π(1) excited states were observed. The 1–0 band of SnO A–X is unperturbed, whilst the v′= 3 and v′= 4 levels of SnO A1Π are perturbed. The v′= 3 level of A1Π and the v′≈ 13 level of b′3Π(1) show a strong mutual perturbation. The v′= 4 level of A1Π is somewhat more weakly perturbed by a 1Δ(1) or 3Π(2) state. Analysis of the spectra of the A–X and b′–X transitions is described.Lifetimes (τ0) of selected ro-vibrational states of the A1Π and b3Π(1) manifolds, and quenching rate constants with O2(kM), are reported for the first time as follows:—A1Π, v′= 1 : τ0= 160 ± 20 ns; kM=(2.2 ± 0.6)× 10–10 cm3 s–1; A1Πv′= 3 : τ0= 140 ± 10 ns; kM=(6.9 ± 0.6)× 10–10 cm3 s–1; A1Πv′= 4 : τ0= 130 ± 20 ns; kM≤ 1.4 × 10–10 cm3 s–1; b′3Π(1), v′= 14 : τ0= 580 ± 34 ns; kM=(3.6 ± 1.0)× 10–11 cm3 s–1