Single-mode Dye Laser Research Articles

High-resolution hyperfine spectroscopy in real space

A new experimental technique is presented for the observation of high-resolution hyperfine spectra in real space. The method is demonstrated for the case of the hyperfine spectrum of a single rotational line of iodine. Light from a single-mode ring dye laser, which intersects a supersonic molecular jet, excites only those velocity groups for which one of the hyperfine components is properly Doppler shifted into resonance. This new method is useful for spectral measurement and for the characterization of molecular beams.

Autoionization rates and energy levels of triplet nf, v=1 Rydberg states of H2.

We have measured the linewidths of 35 different triplet Rydberg states of the ${\mathrm{H}}_{2}$ molecule with quantum numbers n=10--22, L=3, v=1, and R=0--4. An 18-eV electron beam excites a collimated ${\mathrm{H}}_{2}$ beam to the metastable c(2p${)}^{3}$${\mathrm{\ensuremath{\Pi}}}_{\mathit{u}}$ state. Stepwise excitation using two counterpropagating cw single-mode dye laser beams excites the metastable molecule first to an intermediate state [(3d${)}^{3}$\ensuremath{\Sigma} or (3d${)}^{3}$\ensuremath{\Pi}] and then to a triplet nf Rydberg state. The linewidths for the nf Rydberg states give the autoionization rates, which agree satisfactorily with the polarizability--quadrupole-moment long-range interaction model. We also have measured the transition frequencies between these states to an accuracy of 0.002 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. We use these measurements to derive the ionization potential of the metastable triplet state to an accuracy of 0.020 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ and the energy difference between the metastable and ground states of ${\mathrm{H}}_{2}$ to an accuracy of 0.025 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$.

A new single-mode laser equation

A new complex field amplitude equation for the single-mode laser with several colored multiplicative noises is derived. The relation between our equation and the single-mode dye laser equations with gain noise is discussed. To study the statistical properties of the single-mode laser using the equation we obtained, an effective Fokker-Planck equation (EFPE) in which the laser intensity is decoupled from the phase variable is derived.

Narrow Linewidth Operation of a Pulsed Grazing-incidence Dye Laser

Abstract We have designed and tested a pulsed single-mode dye laser for use as the master oscillator in a laser isotope separation (LIS) system. The design features a grazing incidence, or Littman type, cavity which is pumped at a repetition rate of up to 6 kHz by a copper vapour laser to produce a single-mode nearly diffraction-limited beam at over 1% efficiency. Operating on the dye Rhodamine B the laser can be tuned over the range 570–590 nm of interest for LIS.

Depolarization of optically pumped sodium atoms by wall surfaces

The polarizations of sodium atoms optically pumped by a single-mode cw ring dye laser were measured as a function of the pumping power, sodium-vapor thickness, and external magnetic field for Pyrex glass and copper walls with and without dry-film coating. Observed quantities were analyzed by a simple optical pumping model in which the effect of the radiation trapping was taken into account. Assuming that the depolarization of the sodium atom was mainly induced by the local magnetic field at the sodium atom during its adsorption on the wall surface, the calculations could successfully reproduce the observed polarizations.

Time dependence of hole spectrum due to dispersive burning kinetics in dye-doped polymers

Time evolution of a persistent hole spectrum has been investigated for dyes doped in polyvinyl alcohol films at 2 K. The zero-phonon hole profile measured for resorufin using a single-mode dye laser has been found to be nearly Lorentzian even in the case of relatively deep holes. The observed fluence-dependent depth and width of the zero-phonon hole are reproduced well by the numerical simulation based on a dispersive burning-kinetics model. It is pointed out that a large distribution of the burning rate is responsible for the fluence-dependent hole broadening. Time evolution of the phonon-sideband hole simulated using the same model is also compared with the experimental data. It is shown that the low-energy sideband hole is enhanced when the burning kinetics is dispersive.

Multiple Photochemical Hole Burning of Tetraphenylporphine Derivatives

We have studied multiple photochemical hole burning of tetraphenylporphine derivatives in the frequency domain. More than 100 holes were produced in an inhomogeneously broadened absorption band at liquid helium temperature. High resolution monitoring of photochemical holes by scanning the wavelength of a single-mode dye laser proves that the potential area density of recording reaches up to 1000 holes/laser spot. We also carried out multiple photochemical hole burning in a focused laser spot, and produced more than 10 holes. These experiments indicate that tetraphenylporphine derivatives are suitable materials in practical applications of photochemical hole burning.

The 5dnf J=4 and 5 autoionising Rydberg series in barium: experiment and MQDT analysis

Accurate values for the energies and linewidths of the 5dnf J=5, 4 (n=4-50) autoionising Rydberg series of neutral barium have been collected using either a single-mode CW ring dye laser or a Nd:YAG pumped pulsed dye laser and a beam of neutral atoms in the metastable 5d2 1G4 and 5d2 3F states. The interactions between series within the configuration converging to the 5d3/2 and 5d5/2 ionisation limits as well as the continuum interactions (for J=5) have been analysed using multichannel quantum defect theory (MQDT) in the 'phaseshifted reaction matrix' formalism. Good agreement between experiment and MQDT calculations is obtained; however, not all interaction parameters could be determined from the available data.

Multiplicative colored noise in a dye laser at steady state.

The steady-state intensity fluctuations of a single-mode dye laser are investigated when the laser is operated far above threshold. An analytic expression for the variance of the laser intensity is obtained when both additive white and multiplicative colored noise are included in the laser model. The result is in excellent agreement with the measurements of Kaminishi, Roy, Short, and Mandel [Phys. Rev. A 24, 370 (1981)].

Manipulation of level-crossing signals using narrow-band or pulsed laser excitation

Level-crossing experiments yielding Doppler-free signals are normally performed using a CW light source with a broad spectral distribution ("white" excitation), and the signals obtained are described by a well-known formula due to Breit. By using a single-mode dye laser or a pulsed laser for the excitation, strong modifications of level-crossing signals can be obtained. Profound changes in hyperfine structure crossing signals are demonstrated in experiments, performed in a cell, on the 9 2D3/2 state of 133Cs. Practical utilisation of unconventional excitation in level-crossing and optical double resonance spectroscopy is discussed.

Laser spectroscopy on the A0 +-X1Σ + transition of T1I

The first excited electronic state of TII was investigated by laser excitation and laser fluorescence spectroscopy. Almost completely resolved rotational fine structure was observed with the help of a collimated molecular beam and a single-mode cw dye laser. From the derived Dunham parameters Y lk a RKR potential for the excited state is calculated. The unusual shape of the potential energy curve can be understood as originating from an avoided crossing of the ionic ground-state potential and a non-bonding covalent state of the atomic asymptote (6p) 2P 1 2 (TI)+(5p) 5 2P 3 2 (I).

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.

High-resolution coherent VUV spectroscopy of NO[C 2Π(1)∼B 2Π(10), B 2Π(11)] and CO[B 1Σ(0)

The outputs of two single longitudinal mode dye lasers have been combined by the processes of four-wave sum and difference frequency mixing in Hg vapour to produce tunable, coherent VUV radiation in the ranges 110–116 nm and 178–195 nm, respectively. The dye laser pulses of 500 MHz bandwidth (fwhm) produced a VUV pulse of bandwidth 3 GHz (0.1 cm −1, fwhm).The bandwidth was tested by recording UF spectra of NO[B 2Π←X 2Π(10, 0) and (11, 0)] and CO[B 1Σ +←X 1Σ +(0, 0)]. This VUV light was also used to excite single rovibrational levels of NO or CO in a supersonic jet and the resulting radiative decay was monitored by time-resolved fluorescence detection. Collision-free radiative lifetimes were measured for the first time for several low J rotational levels of B 2Π(10) and B 2Π(11) of NO. The B 2Π(10) level showed a variation in lifetime of 60.6±2.0 to 39.3±5.0 ns from J = 1 2 to J = 11 2 while B 2Π(11) showed no variation in its lifetime of 14.0±0.4 ns. Linewidth measurements for the C 2Π(1) level infer a lower limit of 0.03 ns for its lifetime. Lifetimes were also measured for B 1Σ +(0) of CO whose radiative decay revealed severe radiation trapping effects at pressures above 10 −5 Torr.

Measurements of 22Ne-20Ne Isotope Shifts by Laser-Induced Line Narrowing in Three-Level Systems

Application of laser-induced absorption line narrowing (ALN) to neon isotope shift investigations in the stretched three-level systems 1 s5-2p4-3 s2 and 1 s4-2 p4-3 s2 is reported. The measurements have been performed with a frequency and intensity-stabilized 633-nm He-Ne probe laser and with a tunable single-mode R6G dye laser. Utilization of longitudinal magnetic modulation to the neon gas absorber yields background-free resonance signals. Measurements of 594.5-, 609.6-, and 633-nm 22Ne-20Ne isotope shifts result in (1712 ± 8) MHz, (1753 ± 8) MHz, and (904 ± 8) MHz, respectively. These values agree with previous data.

Modulation techniques in three-level laser spectroscopy of a neon discharge

The interaction between a chopped laser pump beam and a neon discharge is compared with the interaction between the unchopped beam and a Zeeman modulated discharge response. Experimental sensitivity and reliability is obtained by unconventionally utilizing a fixed frequency and intensity stabilized single mode 633 nm He-Ne laser as a probe and a tunable single mode dye laser as a pump. Neon atoms in the metastable first excited state 1s 5 are pumped to the lower energy level of the (633 nm) 2p 4-3s 2 transition. Pumping to uncoupled nearby levels of 2p 4 is also studied. Several gigahertz wide backgrounds originating from the plasma ionization changes induced by the chopped pump beam are shown to be eliminated by the more adiabatic magnetic modulation technique. Connections between high resolution spectroscopy, polarization spectroscopy line shape asymmetries and optogalvanic spectroscopy are discussed. The usefulness of the magneticmodulation technique in high resolution studies is demonstrated.

Effects of colored pump noise on intensity correlations of a single-mode dye laser.

Recent theoretical analyses of the single-mode laser with colored-noise pump fluctuations have allowed the detailed prediction of the short-time behavior of the intensity autocorrelations of such a laser. In particular, a rounding off of the intensity correlation function on the time scale of the correlation time of the pump fluctuations has been predicted. We present results from experiments performed on a single-mode dye-laser system that clearly confirm these predictions. Numerical simulations of the laser Langevin equations including the colored-noise pump fluctuations are used to fit the experimental results.

Radiative lifetimes of Am I atomic levels.

The lifetimes of several atomic levels of Am I that are connected by electric dipole transitions to the ground state have been measured. The Am atoms were excited by light pulses from a cw single-mode dye laser with the aid of an optoacoustic modulator. The decay curve of the delayed emitted photons was measured by counting single photons in the beam-off periods. The lifetimes of 14 levels in the wavelength region between 6405 and 4265 A were measured using Am-metal vapor. The metallic Am was obtained by reducing AmO/sub 2/ with La at 1500 /sup 0/C in a high-vacuum system and collecting Am on a catcher foil. The Am vapor was then produced by controlled reevaporation from the foil at a temperature of about 800 /sup 0/C. These lifetime measurements, in combination with the line intensities from a hollow-cathode discharge, allow the identification of the Am transitions homologous to the strong Eu I transitions from the y/sup 8/P/sub 5/2,7/2,9/2/ terms to the ground state.

Stabilization of a single mode dye laser to a HeNe laser using magnetic modulation of a three-level neon system

We describe a simple stabilization method where a tunable single mode (594.5 nm) cw dye laser is locked to a stabilized (633 nm) HeNe laser via the 1s 5-2p 4-3s 2 Ne transitions. By using longitudinal Zeeman modulation of the absorber and a circularly polarized HeNe laser beam derivative signals are obtained. Utilization of routine lock-in techniques produces a dye laser frequency stability comparable with that of the reference HeNe laser.

Optical-optical double-resonance spectroscopy of SrF: The F 2Σ +-B 2Σ + and G 2Π-B 2Σ + systems

Sub-Doppler optical-optical double-resonance spectra of SrF were recorded using two single-mode cw dye lasers. Via the intermediate state B 2Σ +, the F 2Σ + and G 2Π states were observed in the 32000 to 35000 cm −1 region above the ground state. The (1, 0), (2, 0), and (3, 0) bands of the F 2Σ +-B 2Σ + transition and the (0, 0) band of the G 2Π-B 2Σ + transition were rotationally analyzed. Rotational and vibrational constants for the F 2Σ + state and rotational constants for the G 2Π state are reported.

Observation and characterization of a doubly excited electronic state of 39K 2

Supersonic nozzle beam and optical-optical double resonance techniques using a cw single-mode ring dye laser as a pump and a narrow-band pulsed dye laser as a probe have been used to make the first spectroscopic study of a doubly excited electronic state ( 1Σ g −) of 39K 2 above the (lowest) 2Σ g + state of K 2 +. Molecular constants (in cm −1) are T e = 36599.7(1), ω e = 43.47(3), ω eχ e = 0.225 (3), B e = 0.0444(3), α e = 0.00027 (5), and R e = 4.41 Å.