Cyril Drag

Experimental versus theoretical rates for photoassociation and for formation of ultracold molecules

We report on the spectra of the long-range attractive molecular states of the Cs/sub 2/ dimer below the dissociation limits 6s+6p/sub 1/2/ and 6s+6p/sub 3/2/ which are accessible by molecular photoassociation of cold Cs atoms. For the states O/sub u//sup +/ and O/sub g//sup -/(6s+6p/sub 3/2/), we have performed trap-loss measurements, which are in good agreement with the theoretical calculations, performed in a perturbative approach. For the O/sub g//sup -/ and 1/sub u/(6s+6p/sub 3/2/) states, we observe, after spontaneous decay of the electronically excited molecules, the formation of translationally cold molecules. A rate of formation of cold molecules of the order of /spl sim/10/sup 6/ molecules per second is obtained in the case of the state O/sub g//sup

Pulsed photodetachment microscopy and the electron affinity of iodine

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Frequency stabilization at the kilohertz level of a continuous intracavity frequency-doubled singly resonant optical parametric oscillator

Photodetachment microscopy is carried out on a beam of 127I− ions with a nanosecond pulsed laser. The photoelectron interferograms are recorded by means of a digital camera that images the light spots produced by the amplified photoelectrons on a phosphor screen. This is the first implementation of such an optical imaging technique in photodetachment microscopy. Due to their sensitivity to the photoelectron energy, the recorded electron interferograms can be quantitatively analysed to produce a measure of the electron affinity of iodine eA(127I) with an accuracy improved by more than a factor of 2 with respect to the best previous measurement. The result is 2467 287.4(29) m−1 or 3.059 0463(38) eV.

High spectral purity and tunable operation of a continuous singly resonant optical parametric oscillator emitting in the red.

A continuous intracavity frequency-doubled singly resonant optical parametric oscillator (OPO) is stabilized to the side of the transmission peak of a medium finesse Fabry-Perot cavity. The narrow bandwidth of the frequency noise of this OPO allows this simple scheme to lead to a stability of a few kilohertz with respect to the locking etalon. The system, operating in the visible domain, remains locked for more than 1 h.

Photodetachment microscopy of the P, Q, and R branches of the OH−(v=0) to OH(v=0) detachment threshold

Continuous-wave oscillation of a singly resonant optical parametric oscillator operating from 619 to 640 nm has been obtained. Parametric gain is created in a MgO-doped periodically poled stoichiometric lithium tantalate crystal pumped at 532 nm. 100 mW of single-frequency red light have been generated. The signal frequency is tunable, and its frequency stabilization on an external reference has been achieved.

Actively mode-locked optical parametric oscillator.

A photodetachment experiment is performed on the v=0-->v=0 OH(-) detachment threshold. The weak O and S branches provide a signal strong enough to make amplitude measurements on all five O, P, Q, R, and S branches possible, which are used to fix the formulas for their relative intensities. Photodetachment microscopy is applied to 15 different thresholds of the P, Q, and R branches. The quantitative analysis of the interference patterns obtained does not show any effect of the dipole moment of OH, but yields a new measurement of the rotational parameters of OH(-)(v=0) and of the electron affinity of the molecule. The new recommended value for the electron affinity of (16)O(1)H is 14 740.982(7) cm(-1) or 1.827 648 7(11) eV.

The fine structure of S and S − measured with the photodetachment microscope

We report on what we believe to be the first demonstration of active mode locking of an optical parametric oscillator. An acousto-optic modulator is inserted into a nearly degenerate (approximately 1064 nm) and doubly resonant optical parametric oscillator based on periodically poled LiNbO3 and pumped with the second harmonic of a quasi-continuous-wave single-frequency Nd:YAG laser. When the modulation frequency is matched to the free spectral range of the cavity (120 MHz), a pulsed regime is observed, with pulse durations as short as 700 ps.

Single-frequency and tunable operation of a continuous intracavity-frequency-doubled singly resonant optical parametric oscillator

Photodetachment microscopy of a beam of 32S− ions makes it possible to measure the detachment thresholds corresponding to different fine-structure levels of the negative ion S− and the neutral atom S. The electron affinity of sulfur, at 2.077 eV, is well suited for detachment by a tunable dye laser, which provides a third way of measuring neutral S fine structure, besides VUV spectroscopy of S I lines and direct fine-structure resonance spectroscopy. The fine-structure intervals are found to be 48 353.52(34) m−1 for the 2P1/2 − 2P3/2 energy difference in S−, and 39 605.87(32) m−1 for the 3P1 − 3P2 one in S (with expanded uncertainties), consistent with an independent measurement of the 3P0 − 3P1 interval. The new recommended electron affinity for isotope 32 of sulfur is 1675 297.60(42) m−1, or 2.077 104 18(71) eV.

Spectrotemporal dynamics of a picosecond OPO based on chirped quasi-phase-matching

A widely tunable continuous intracavity-frequency-doubled singly resonant optical parametric oscillator based on MgO-doped periodically poled stoichiometric lithium tantalate crystal is described. The idler radiation resonating in the cavity is frequency doubled by an intracavity BBO crystal. Pumped in the green, this system can provide up to 485 mW of single-frequency orange radiation. The system is continuously temperature tunable between 1170 and 1355 nm for the idler, 876 and 975 nm for the signal, and between 585 and 678 nm for the doubled idler. The free-running power and frequency stability of the system have been observed to be better than those for a single-mode dye laser.

Stimulated Raman scattering in an optical parametric oscillator based on periodically poled MgO-doped stoichiometric LiTaO3.

We report on the first experimental investigation of the spectral dynamics of a synchronously pumped optical parametric oscillator (OPO) by use of dispersive Fourier transformation. For standard pumping rates, we observe a reproducible steady-state pulse-to-pulse spectrum. However, at high pumping levels, the OPO delivers pulse trains with nontrivial oscillatory spectral patterns. So as to benefit from a tailored broadband gain spectrum, the investigated OPO contains a chirped quasi-phase matching (QPM) nonlinear crystal. We explore the specific impacts of using such a remarkable parametric amplification medium where nonlinearly coupled frequencies vary with position. Depending on the QPM chirp rate sign, a red- or blue-shift of the emitted wavelength occurs when the OPO is switched on, leading to different spectral steady-states. These singular spectrotemporal dynamics are evidenced and explained for the first time.