Katarzyna Bielska

The air-broadened, near-infrared CO2 line shape in the spectrally isolated regime: Evidence of simultaneous Dicke narrowing and speed dependence

Frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) was employed to measure air-broadened CO(2) line shape parameters for transitions near 1.6 μm over a pressure range of 6.7-33 kPa. The high sensitivity of FS-CRDS allowed for the first measurements in this wavelength range of air-broadened line shape parameters on samples with CO(2) mixing ratios near those of the atmosphere. The measured air-broadening parameters show several percent deviations (0.9%-2.7%) from values found in the HITRAN 2008 database. Spectra were fit with a variety of models including the Voigt, Galatry, Nelkin-Ghatak, and speed-dependent Nelkin-Ghatak line profiles. Clear evidence of line narrowing was observed, which if unaccounted for can lead to several percent biases. Furthermore, it was observed that only the speed-dependent Nelkin-Ghatak line profile was able to model the spectra to within the instrumental noise level because of the concurrent effects of collisional narrowing and speed dependence of collisional broadening and shifting.

Pound-Drever-Hall-locked, frequency-stabilized cavity ring-down spectrometer

We describe a high sensitivity and high spectral resolution laser absorption spectrometer based upon the frequency-stabilized cavity ring-down spectroscopy (FS-CRDS) technique. We used the Pound-Drever-Hall (PDH) method to lock the probe laser to the high-finesse ring-down cavity. We show that the concomitant narrowing of the probe laser line width leads to dramatically increased ring-down event acquisition rates (up to 14.3 kHz), improved spectrum signal-to-noise ratios for weak O(2) absorption spectra at λ = 687 nm and substantial increase in spectrum acquisition rates compared to implementations of FS-CRDS that do not incorporate high-bandwidth locking techniques. The minimum detectable absorption coefficient and the noise-equivalent absorption coefficient for the spectrometer are about 2×10(-10) cm(-1) and 7.5×10(-11) cm(-1)Hz(-1/2), respectively.

High-Accuracy CO(2) Line Intensities Determined from Theory and Experiment

Atmospheric CO(2) concentrations are being closely monitored by remote sensing experiments which rely on knowing line intensities with an uncertainty of 0.5% or better. Most available laboratory measurements have uncertainties much larger than this. We report a joint experimental and theoretical study providing rotation-vibration line intensities with the required accuracy. The ab initio calculations are extendible to all atmospherically important bands of CO(2) and to its isotologues. As such, they will form the basis for detailed CO(2) spectroscopic line lists for future studies.

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.

Absolute frequency determination of molecular transition in the Doppler regime at kHz level of accuracy

Abstract We measured absolute frequency of the unperturbed P7 P7 O2 B-band transition ν 0 =  434783.5084857(82) GHz and the collisional self-shift coefficient δ = − 9.381 ( 62 ) × 10 − 21  GHz/(molecule/cm3). With Doppler-limited spectroscopy we achieved the relative standard uncertainty of 2 × 10 − 11 on line position, typical for Doppler-free techniques. Shapes of the spectral line were measured with a Pound-Drever-Hall-locked frequency-stabilized cavity ring-down spectrometer referenced to an 88Sr optical atomic clock via an optical frequency comb.

Two independent strontium optical lattice clocks for practical realization of the meter and secondary representation of the second

We report a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. This allows verification of relative stability of both optical standards. The absolute frequency of the clocks can be roughly verified by the use of an optical frequency comb with the GPS-disciplined Rb frequency standard or, more accurately, by a long distance stabilized fiber optic link with the UTC(AOS) and UTC(PL) via the OPTIME network.

Background gas induced collision shift for a Sr spin-forbidden transition

Buffer gas induced collision shift for the 88Sr 1S0-3P1 transition is investigated by precision saturation spectroscopy of thermal gas in a heat cell. The cell was filled with rare gases of helium, neon, argon, and xenon as buffer gases. Helium showed the largest fractional shift coefficient of 1.6x10-9 Torr-1. The disagreement between our experiments and simple impact calculations indicates effective atom losses from zero-velocity class which contributes to saturated absorption spectroscopy. The result could be useful to evaluate the background gas collision shift of Sr lattice clocks. Keywords: collision, saturated absorption spectroscopy, lattice clock, optical clock, density shift

Buffer-gas-induced collision shift for the Sr 88 S 1 0 − P 3 1 clock transition

Precision saturation spectroscopy of the

Towards Polish Optical Clock with Cold Strontium Atoms, present status and performance

^{88}{\rm Sr} ^1S_0-^3P_1