R. S. Trawiński

Cavity ring-down spectroscopy of the oxygen B-band with absolute frequency reference to the optical frequency comb

Absolute positions of several oxygen B-band lines were measured with the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer. The frequency axis of spectra was linked to the optical frequency comb. Achieved uncertainties of line positions are between 0.9 and 2.9 MHz. Self-pressure shifts coefficients are also reported.

Active control of the Pound-Drever-Hall error signal offset in high-repetition-rate cavity ring-down spectroscopy

A new approach to realizing the Pound–Drever–Hall (PDH) error signal offset correction is presented. The proposed setup and correction procedure allow one to control not only the effect of amplitude modulation of the error signal, but also other sources of offsets that are present in the PDH feedback loop. This technique significantly improves laser frequency locking in high-repetition-rate cavity ring-down spectroscopy (CRDS) by allowing one to recover a tight PDH lock within 1 ms after switching off the probe laser beam. We apply the PDH error signal offset correction to CRDS measurements of the weak 16O2 B-band R7 Q8 line. The resulting spectra taken at a pressure of 1.2 kPa had a signal-to-noise ratio of ~8000:1.

Strontium optical lattice clocks for practical realization of the metre and secondary representation of the second

We present a system of two independent strontium optical lattice standards probed with a single shared ultranarrow laser. The absolute frequency of the clocks can be verified by the use of Er:fiber optical frequency comb with the GPS-disciplined Rb frequency standard. We report hertz-level spectroscopy of the clock line and measurements of frequency stability of the two strontium optical lattice clocks.

Low-pressure line-shape study in molecular oxygen with absolute frequency reference

We present a line-shape analysis of the rovibronic R1 Q2 transition of the oxygen B band resolved by the Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectroscopy technique in the low pressure range. The frequency axis of the spectra is linked by the ultra-narrow diode laser to the optical frequency comb in order to measure the absolute frequency at each point of the recorded spectra. Experimental spectra are fitted with various line-shape models: the Voigt profile, the Galatry profile, the Nelkin-Ghatak profile, the speed-dependent Voigt profile, and the speed-dependent Nelkin-Ghatak profile with quadratic and hypergeometric approximations for the speed dependence of collisional broadening and shifting. The influences of Dicke narrowing, speed-dependent effects, and correlation between phase- and velocity-changing collisions on the line shape are investigated. Values of line-shape parameters, including the absolute frequency of the transition 435685.24828(46) GHz, are reported.

Effect of dissociative recombination on spectral line profiles in neon glow discharge

In the present study we have shown that the dissociative recombination of Ne2+ ions which gives rise to non-thermalized Ne atoms may be regarded as the main process responsible for the distortion of the profiles of the 753.5 and 754.4 nm neon lines. The distorted profiles were analysed as a superposition of the Ballik profile for thermalized atoms and the modified Ballik profile for non-thermalized atoms and the Lorentzian and Gaussian widths as well as the relative density of non-thermalized and thermalized atoms have been determined. We have found for the dissociation energy of the neon molecular ion Ne2+ in the 2 Sigma u+ state the value D=(1.20+or-0.08) eV. We have also found for the 3d6 excited neon atoms of speed 1275 m s-1 the excitation transfer cross section Q3d6 with a value Q3d6=(39+or-15)*10-16 cm2.

On the role of Dicke narrowing in the formation of atomic line shapes in the optical domain

The purpose of this work is to verify the possibility of the observation of the Dicke narrowing of atomic spectral lines in the optical domain. As an example we have chosen experimental results obtained by means of a laser-induced fluorescence method for the 114Cd 326.1 nm line perturbed by xenon. Experimental results were carefully reanalysed using a line shape model which takes into account the speed dependence of collisional broadening and shifting, the velocity-changing collisions and the collision-time asymmetry. We have found no convincing evidence for the occurrence of Dicke narrowing of the 326.1 cadmium line perturbed by xenon. The Dicke narrowing (if it occurs at all) appears to be smaller than that resulting from the estimation based on the accessible data describing the diffusion of Cd in Xe. As a source of this behaviour the correlation between velocity-changing and dephasing collisions was indicated.

Non-adiabatic approach to the asymmetry of pressure broadened spectral lines

Abstract A semi-classical formula for the asymmetry of the profile of pressure broadened spectral lines, which takes into account non-adiabatic processes is derived. The resultant spectrum is shown to be given as a linear combination of the Lorentzian and dispersion profiles. The line profile asymmetry can be evaluated in cases when the degeneracy of both the initial and final states is important.

Low pressure broadening and shift of the cadmium intercombination line 326.1 nm (5 1S0-5 3P1) perturbed by He and Ne

The collisional broadening and shift of the 114Cd intercombination line lambda =326.1 nm (5 1S0-5 3P1) perturbed by He and Ne have been investigated using a pressure-scanned Fabry-Perot interferometer. The values of pressure broadening and shift coefficients determined from the experiment compared with those calculated by Czuchaj and Sienkiewicz (1987) and with values resulting from the Lennard-Jones potential.

Self-referenced, accurate and sensitive optical frequency comb spectroscopy with a virtually imaged phased array spectrometer

We present a cavity-enhanced direct optical frequency comb spectroscopy system with a virtually imaged phased array (VIPA) spectrometer and either a dither or a Pound-Drever-Hall (PDH) locking scheme used for stable transmission of the comb through the cavity. A self-referenced scheme for frequency axis calibration is shown along with an analysis of its accuracy. A careful comparison between both locking schemes is performed based on near-IR measurements of the carbon monoxide ν=3←0 band P branch transitions in a gas sample with known composition. The noise-equivalent absorptions (NEA) for the PDH and dither schemes are 9.9×10(-10) cm(-1) and 5.3×10(-9) cm(-1), respectively.

Low-pressure broadening and shift of 3p54s-3p5np (n=4, 5, 6) argon spectral lines perturbed by He, Ne, Ar

Low-pressure broadening and shift of three spectral lines of argon: 667.7 nm (3p54s-3p54p), 430.0 nm (3p54s-3p55p) and 360.6 nm (3p54s-3p56p), emitted from a low current glow discharge in pure argon, Ar-Ne and Ar-He mixtures have been investigated by means of a Fabry-Perot interferometer. The values of the pressure broadening and shift coefficients are determined.