Doppler-free Two-photon Excitation Research Articles

Doppler-free two-photon spectrum of the 0 00 band of the à 1B 1←X̃ 1A 1 transition in difluorodiazirine, F 2CN 2

The Doppler-free two-photon excitation spectrum of the vibrationless à 1B 1←X̃ 1A 1 transition of difluorodiazirine (F 2CN 2) has been recorded with a resolution of 15 MHz using a cw single-mode dye laser coupled to an external concentric resonator. The asymmetric rotor spectrum has been analysed and more than 350 lines randomly selected from all five branches were assigned in order to fit the ground- and excited-state rotational and quartic centrifugal distortion constants. From the rotational constants the r NN and r FF distances in the ground X̃ 1A 1 and excited à 1B 1 state were determined. The geometry change upon excitation is found to be Δ r NN = 3.89(2) pm and Δ r FF = −4.09(2) pm. No perturbation in the rotational structure of the 0 0 0 band has been found. This points to a small singlet-triplet coupling matrix element in the small molecule limit.

Emission spectra from single rovibronic quantum states in S1 benzene after Doppler-free two-photon excitation

Dispersed emission from single rovibronic quantum states in S1 benzene is measured after Doppler-free two-photon excitation under low pressure conditions (0.3 Torr). This was made possible by a long-term stabilization of the single-mode dye laser yielding a stability of better than 1 MHz/h. The emission spectra of unperturbed rotational levels in the 141 and the 14111 vibronic states reveal a great number of detailed results on Duschinsky rotation and long-range Fermi resonances in the electronic ground state. By contrast, it is seen that the emission spectra from perturbed rovibronic states are contaminated by additional bands. The analysis of these bands leads in most cases to an identification of the coupled dark background state and the responsible rotation–vibration coupling process (H42 resonances). The emission spectra clearly demonstrate that even for a density of states of 60 1/cm−1, coupling in S1 benzene is still selective and far from the statistical limit. It is further demonstrated that the dark and the light states are more efficiently mixed by short-range couplings with coupling matrix elements of some GHz than by long-range Fermi resonances.

Collisions between Sr Rydberg atoms of intermediate and high principal quantum numbers and noble gases at thermal energies

Pressure shift and broadening measurements of 5snd 1D2 and 5snd 3D2 Rydberg states of Sr I due to Xe have been performed in the range 8<or=n<or=35 by means of Doppler-free two-photon excitation, combined with thermionic detection and the use of a molecular frequency standard. The data show striking differences between pressure shifts and broadenings of singlet and triplet states, which up to now have not been predicted by theory.

Time evolution of individual rotational states after pulsed Doppler-free two-photon excitation: Influence of perturbations in S1 benzene

Single rovibronic level excitation has been demonstrated for a molecule representing the statistical limit of a nonradiative electronic relaxation process. Resolution of the complex 1410 two-photon band of benzene was possible after elimination of the Doppler broadening in a Doppler-free two-photon absorption process with narrow bandwidth pulsed laser light and allowed for selective excitation of individual rotational states. Fluorescence decay measurements of these states under low pressure conditions display a pure exponential behavior and reveal that the nonradiative rate is independent of the rotational quantum numbers J, K for an electronic nonradiative relaxation process in the statistical limit. The decrease in lifetime found for perturbed states is attributed to the mixing with a background state containing quanta of an accepting mode.

Sub-doppler two-photon spectrum of asymmetric rotor molecules: analysis of the qqQ rotational branch of the S 1( 1B 2u)14 1 ← S 0( 1A 1g) system of benzene- d1

The Doppler-free two-photon excitation spectrum of the qqQ branch of the 14 1 0 vibrational band of the S 1( 1B 2u) ← S 0( 1A 1g) transition of benzene- d 1 has been recorded using a cw single-mode dye laser coupled to an external concentric resonator. The spectrum has been analysed using a non-rigid Watson Hamiltonian. More than 200 lines with J up to 20 have been assigned and the rotational constants which best reproduce the spectrum are A 1 v = 0.181435, B 1 v = 0.169990, C 1 v = 0.089055 cm −1. The K a = odd lines of the qqQ 5( J) subbranch show small and quite regular perturbations of 60 ± 5 MHz which are probably due to a coupling to another vibrational state of the S 1 manifold.

Doppler-free two-photon excitation of238U

A theoretical and experimental study of resonantly enhanced two-photon absorption in 238U vapour excited by two continuous wave dye lasers is presented. Good quantitative agreement between theory and experiment is found. In particular the central prediction of the theory, that antiparallel laser beams of modest intensity can pump an appreciable fraction of the Maxwell velocity distribution, has been checked directly by measuring the spectral width of the fluorescence from the two-photon excited level.

Doppler-free two-photon excitation of nitric oxide with frequency-stabilized cw dye laser radiation

Doppler-free two-photon transitions are induced in nitric oxide with blue, narrowband, tunable radiation generated by a frequency-stabilized cw dye ring laser. The recorded two-photon spectra provide a precise measurement of the spin-rotation splitting of the excited rotational levels (A 2∑ +, ν' = 0) N' = 1 to N' = 19. The splitting constant γ is determined to be γ = 80.35(15) MHz.

Influence of Singlet-Triplet Mixing on the Hyperfine Structure of5sndRydberg States inSr87

A systematic study of the hyperfine structure of $5snd$ $^{1}D_{2}$ and $^{3}D_{2}$ states of $^{87}\mathrm{Sr}$ was carried out by Doppler-free two-photon excitation. In the region of strong singlet-triplet mixing around $n=16$, the hyperfine structure exhibits a marked $n$ dependence which is related to the amount of singlet-triplet mixing.

Doppler-free two-photon laser excitation of the vacuum ultraviolet absorption spectrum of CO

The two photon excitation of the vacuum ultraviolet fourth positive band system (A1π − X1∑+) produced by frequency doubling the output of a nitrogen laser pumped tunable dye laser was reported previously where the (0–0) through (9–0) bands were observed under low resolution conditions [1]. The present work describes a high resolution, Doppler-free excitation of the fourth positive CO spectrum under high resolution conditions and with an absolute wavelength calibration that appears to be an order of magnitude more accurate than can be obtained by conventional grating spectroscopy.

ʌ-type doubling and spin-rotation splitting of NO, measured in simultaneous one- and two-photon laser spectroscopy

Doppler-free two-photon excitation of NO A 2Σ + by visible dye laser radiation is recorded simultaneously with single-photon absorption of frequency-doubled UV laser light. The measurement of the frequency difference between corresponding lines in the one- and two-photon spectrum provides a new method for a direct optical determination of Λ-type doubling in the X 2Π ground state. In addition, the spin-rotation splitting of the A 2Σ + excited state is resolved in the Doppler-free two-photon spectrum.

Hyperfine interaction in the [formula omitted] and the [formula omitted] levels of sodium

We have excited the 4D 3 2 and 4D 5 2 levels of sodium using Doppler-free two-photon excitation. By measuring the polarization rate in zero magnetic field of the fluorescence lines, we have deduced the following values for the hyperfine interaction |A( 4D 3 2 ) | = 0.23 ± 0.12 MHz and |A( 4D 5 2 )| < 0.28 MHz . The value of A( 4D 3 2 ) is in disagreement with the one reported by Schenk and Pillof.

Raman transients observed in Doppler free two-photon excitation

Using Doppler-free two-photon excitation, we have observed the transients produced by the sudden introduction or cut-off of the exciting light. The two-photon excitation is of a particular interest because all the atoms are excited with the same energy detuning from the resonance. We have observed the time-variation of the scattered light for several values of the detuning. The corresponding results show the transition from resonance fluorescence to Raman scattering.

Coherent Two-Photon Excitation by Multiple Light Pulses

We have studied Doppler-free two-photon excitation of atoms with a train of phase-coherent standing-wave light pulses, originating from the same laser pulse. Quantum interference effects produce narrow spectral fringes which have a physical origin similar to that of Ramsey fringes. Linewidths much less than the Fourier-transform limit of an individual light pulse have been observed for the sodium $3S\ensuremath{-}5S$ transition; and a dramatic enhancement of the resonant signal is possible.

Doppler-free resonant two-photon transition for isotope separation

The Doppler-free two-photon transition by the use of two opposing laser beams makes the highly selective excitation of isotopic molecules possible. Saturation and pressure dependence of Doppler-free two-photon excitation with arbitrary amplitudes of the optical fields have been calculated and compared with those of the two-step transition and the single-photon transition. The result at the Doppler limit for low pressure gas reveals that the probability of the selective two-photon excitation with a moderate laser power can be larger than that of the single-photon excitation as well as that of the two-step excitation.