Collisional broadening and shifting of saturated absorption resonances in silicon tetrafluoride

The broadening and shifting of 12 saturated absorption resonances of the SiF₄ gas induced by molecular collisions have been measured in the lasing region of a low-frequency CO₂ laser at the P(30) line of the 9.4-μm band. Values of the collisional broadening are identical accurate to the measurement uncertainty. The collisional shift does not exceed 10% of the collisional broadening. This means that collisions with changes in the internal energy of molecules prevail over dephasing collisions.     

Supernarrow saturated absorption resonances in weakly coupled two resonant optical cavities

The advantages of the weakly coupled two resonant optical cavities (hereinafter referred to as three-mirror cavity) used for observation of the supernarrow saturated absorption resonances are shown. Among these advantages we can name: (a) the possibility to control the intensity in the cavity with the inside absorbing cell which is important when the gain and absorption saturation parameters differ significantly; (b) the resonances observation from the ‘passive’ side of the three-mirror cavity permits us to decrease drastically the influence of the reflected signal from the detector; (c) if instead of the absorbing cell an active system is put in (gain plus absorption), it is possible by tuning the operating mode of the active interferometer to obtain many-fold gain of the supernarrow resonance amplitude. Received: 11 January 2000 / Revised version: 20 June 2000 / Published online: 9 February 2001     

Doppler-free spectroscopy of Mg using uv-visible saturated absorption

Cascade double resonance saturation spectroscopy was performed on the Mg 3s ¹S₀-3p ¹P₁-5s ¹S₀ transitions. A strong dye laser at 571 nm induced an inverted dip on the 285 nm resonance line transmission spectrum probed by a second, frequency doubled, dye laser. New values for the isotopic shifts of the visible transition were obtained.     

Possibility of new resonances in transient nonlinear spectroscopy

We predict the existence of new types of extra resonances in transient four wave mixing from a system with negligible collisions. These new resonances arise from the coherent pumping and disappear in the long time limit. We give explicit results for extra resonances in four wave mixing from several conventonally used systems.     

On the resolving power of high-contrast saturated absorption spectroscopy

Recently Svanberg et al. [Optics Lett. 11 (1986) 138; J. Opt. Soc. Am. B 4 (1987) 462] obtained saturated absorption resonances with subnatural linewidth by working in the regime of high pumping intensities and optically thick atomic samples. We analyze here this new spectroscopic regime, within the formalism of Maxwell-Bloch-type equations, in the case of a Doppler broadened medium having two nearly degenerate but uncoupled resonances. We show that even in this most favourable case it is not possible to resolve spectral features that lie within the natural linewidth.     

Effects of modulation on signals obtained in saturated absorption spectroscopy experiments

An analysis of the useful signals detected in saturated absorption spectroscopy experiments is given. Both Gaussian and plane-wave fields are considered. The various cases of unmodulated, square-wave modulated and sinusoidally modulated saturating beams are examined. It is found that square-wave and sinusoidal modulations give different results. The first is identical to no modulation, and detection at the fundamental frequency records a fraction of the total signal which is also a square wave. The second gives fundamental or higher-harmonic signals each with a very different dependence on the saturation parameter. The signal at the fundamental saturates faster and more completely than that for square-wave modulation. The results suggest experimental methods for the determination of the absolute value of the saturation parameter.     

Intersubband lifetimes in InAs/GaSb superlattices using saturated absorption spectroscopy

We investigate intersubband relaxation rates above the optical phonon energy in a InAs/GaSb superlattice using saturation spectroscopy. A high-intensity free-electron laser tuned to the intersubband transition energy is used to saturate the absorption process revealing picosecond relaxation rates. The effects of the parallel magnetic field and laser energy on the relaxation processes are explored.     

Theoretical detection limit of saturated absorption cavity ring-down spectroscopy (SCAR) and two-photon absorption cavity ring-down spectroscopy

Giusfredi et al. (Phys Rev Lett 104, 110801, 2010), have developed a new approach to cavity ring-down spectroscopy where a saturable sample absorption is determined simultaneously with the cavity loss, providing immunity to changes in cavity loss, thereby allowing for lower analyte detection limit. This paper presents an error analysis that provides predictions of the ultimate sensitivity limits that can be realized with this detection method. In particular, the sensitivity is strongly dependent upon the initial degree of saturation of the sample, and optimal values for this are determined both for photon detector and shot-noise-limited detection of both inhomogeneous and homogeneous broadened spectroscopic lines. Also presented are sensitivity limits expected for two-photon absorption spectroscopy determined by cavity ring-down spectroscopy.     

Detection of saturated absorption spectroscopy at high sensitivity with displaced crossovers

We present an unconventional experimental approach for detecting saturated absorption spectroscopy. Using this approach, crossover peaks are displaced, leaving out peaks corresponding to an atom's natural resonant frequencies. Sensitivity of detection can also be enhanced. Consequently, the spectrum could reflect the energy structure of atoms more explicitly. Without harmful influence from crossovers, the locking range of the error signal is significantly increased and the symmetry of the dispersion line shape is perfectly preserved, so reliability of frequency stabilization can be improved.     

Low-resolution microwave spectroscopy: A new band type

The effects of relaxing two constraints on an earlier force field for benzene and fluorobenzenes have been explored. If the CC/CC ortho, meta, and para interaction constants are allowed to vary independently, they take the values 62, ?34, and 48 N m^?1, respectively. The interesting features of the earlier field are retained with the possible exception that the dependence of the CC stretching constant is less clearly dependent on fluoro substitution on the bond. An attempt to use more reasonable geometries than the regular hexagonal geometry assumed hitherto produced no improvement in the fit and did not alter the field significantly.     

Study of relaxation of molecular iodine by the method of saturated absorption spectroscopy

The paper describes detailed experimental studies of the width, shape and shifts of saturated absorption resonances at the X(v=0, j=13)B(v=43, j=12) transition of molecular iodine. Use of the geometry of oppositely travelling and unidirectional waves in the experiment and study of the luminescence decay under pulsed excitation allowed estimation of the cross-sections of elastic and inelastic scattering of I₂ molecules on the upper and lower levels of transition. The observed nonlinear dependence of width and shift of the saturation resonance on iodine pressure is explained by the influence of elastic collisions with no phase mismatch.     

Saturated absorption spectroscopy: Elimination of crossover resonances with the use of a nanocell

It is demonstrated that the velocity-selective optical pumping/saturation resonances of the reduced absorption in a Rb vapor nanocell with thickness L = λ, 2λ, and 3λ (resonant wavelength λ = 780 nm) allow for the complete elimination of crossover (CO) resonances. We observe well-pronounced resonances corresponding to the F _g = 3 → F _e = 2, 3, and 4 hyperfine transitions of the ⁸⁵Rb D₂ line with line widths close to the natural width. A small CO resonance located midway between F _g = 3 → F _e = 3 and F _g = 3 → F _e = 4 transitions appears only for L ≥ 4λ. The D₂ line (λ = 852 nm) in a Cs nanocell exhibits a similar behavior. From the amplitude ratio of the CO and VSOP resonances, it is possible to determine the thickness of the column of alkali vapor in the range of 1–1000 μm. The absence of the CO resonances for nanocells with L ～ λ is attractive for the frequency reference application and for studying the transitions between the Zeeman sublevels in external magnetic fields.     

Zeeman coherence in saturated absorption

By modulating the saturating beam polarization, it is possible to extract from the probe beam a signal which depends only on the Zeeman coherence Δm = 2 (transverse alignment), and to study velocity changing collisions which do not destroy the alignment. This type of collisions appears to be of small importance in neon, so that width of the saturated absorption curve from alignment is narrower than that from populations.     

A new cell for X-ray absorption spectroscopy study under high pressure

X-ray absorption fine structure （XAFS） spectroscopy is a powerful technique for the investigation of the local environment around selected atoms in condensed matter. XAFS under pressure is an important method for the synchrotron source. We design a cell for a high pressure XAFS experiment. Sintered boron carbide is used as the anvils of this high pressure cell in order to obtain a full XAFS spectrum free from diffraction peaks. In addition, a hydraulic pump was adopted to make in-suit pressure modulation. High quality XAFS spectra of ZrH2 under high pressure （up to 13 GPa） were obtained by this cell.     

A new cell for X-ray absorption spectroscopy study under high pressure

X-ray absorption fine structure (XAFS) spectroscopy is a powerful technique for the investigation of the local environment around selected atoms in condensed matter. XAFS under pressure is an important method for the synchrotron source. We design a cell for a high pressure XAFS experiment. Sintered boron carbide is used as the anvils of this high pressure cell in order to obtain a full XAFS spectrum free from diffraction peaks. In addition, a hydraulic pump was adopted to make in-suit pressure modulation. High quality XAFS spectra of ZrH2 under high pressure (up to 13 Gpa) were obtained by this cell.     

A model-independent description of dt and d3He systems near low-energy resonances

Very important information for the reconstruction of archaeometallurgical processes can be obtained from slags. The determination of the mineralogical and chemical composition of the major components has made it possible to derive the most important operative conditions of the ancient smelting processes. However, the loss of copper in the form of particles mechanically entrained in the slags is also of great interest because it can give us information about possible intermediates.Parts I and II have been published in Hyperfine Interactions 67 (1991) 473 and 70 (1992) 1005.     

Narrow resonances of saturated absorption of the asymmetrical molecule CHFCiBr and the possibility of weak current detection in molecular physics

According to V.S. Letokhov's suggestion the neutral and charged weak currents (in weak interactions) must cause a splitting of the vibrational-rotational levels of left and right molecules by a relative value of 10^-15–10^-16. To detect this effect an experiment is proposed which consists of direct measuring the beat frequency of two frequency stabilized lasers, their references being two identical narrow spectral lines in the vibrational-rotational spectrum of two optical isomers of an asymmetrical molecule. For this purpose one may use narrow saturated absorption resonances of CHFClBr induced in the cw CO₂ laser field. The effects having influence on the reproducibility of the frequency by molecular reference and the necessity of identity conditions for cells with left and right molecules (CHFClBr) are discussed.     

A new technique for Raman spectroscopy in highly absorbing liquid systems

In this paper we describe a new technique for Raman spectroscopy in highly absorbing liquid samples. Such a technique, called Jet Flow Raman Spectroscopy (JFRS) is used in the case of saturated solutions of strong electrolytes such as CuCl₂ and CoCl₂. A comparison of spectra obtained with JFRS and a semicapillary cell is shown. The power of the JFRS technique is also proved with the evidence of a resonant Raman effect in saturated aqueous solutions of CuCl₂.     

Optical absorption resonances of trapped particles

We have previously shown the possibility of the existence of a one-photon resonance with homogeneous width in the center of an absorption line of trapped particles. The results of a detailed investigation of this resonance are given in the first part of the present paper. The second part is devoted to a two-photon resonance in a standing-wave field: the time of coherent interaction with the field is increased for trapped particles, which permits the elimination of transit resonance broadening.