Hanle Resonances Research Articles

Measurement of collisional depolarisation rates in the 4f 66s2 7F levels of Sm by optical field induced circular birefringence

The Hanle resonance investigated as an optical field induced circular birefringence has been applied to studying the collisional depolarisation in the 4f 66s2 7FJ (J not=0) levels of Sm by rare gas perturbers. The measured cross sections for the destruction of orientation in 4f 66s2 7FJ (J=1-6) by He and Ar perturbers are reported. The data for the 7F1 level are compared with previous works.

Optical Haroche and Hanle resonances

It is shown that Haroche and Hanle resonances, known from magnetic resonance, should be observable in an optical resonance experiment in which a narrowband, phase-modulated laser resonantly excites a two-level system. The narrow Haroche resonances should allow the first observation of an optical Bloch-Siegert shift, and may find applications in modulation spectroscopy.

Collision-enhanced Hanle resonances in absorption spectroscopy

The existence of the collision-enhanced Hanle resonances in the 3 2S 1 2 state of Na atoms has been demonstrated as a sharp resonance in absorption spectroscopy. The intensity and the linewidth of these resonances, compared to collision-enhanced Hanle resonances in four-wave mixing, has the same dependence on buffer gas pressure, but the dependences on the laser power and frequency detuning from Na resonance are different.

Fluctuation-induced Hanle resonances in phase conjugation.

We demonstrate the existence of Hanle resonances in four-wave mixing with pump and probe fields derived from the same fluctuating source. A theory of these fluctuation-induced Hanle resonances is developed following the work of Agarwal and Kunasz [Phys. Rev. A 27, 996 (1983)] on four-wave mixing in stochastic fields. Such Hanle resonances are compared with those induced by dephasing collisions.

Pump-noise-induced Hanle effect in forward four-wave mixing.

This is an addendum to our previous publication [Phys. Rev. A 36, 143 (1987)] dealing with cross-correlation--induced resonances in four-wave mixing. The temporal fluctuations of the source lead to well-resolved Hanle resonances in forward four-wave mixing which is in contrast to the dephasing-induced resonance in the same geometry.

Collision- and stochastic-fluctuation-induced Hanle resonances in four-wave light mixing in samarium.

A broadband multimode dye laser, detuned from the \ensuremath{\lambda}=570.68 nm resonance line of Sm atoms, was used to provide three incident beams in the standard phase-conjugate four-wave-mixing geometry. The phase-conjugate output intensity was measured as a function of polarization and external magnetic field configurations, and of the pressure of several buffer gases. We have confirmed the theoretical prediction that correlated stochastic fluctuations in the incident light field make a contribution to the four-wave-mixing signal. Collisional cross sections for reorientation among the m sublevels in the J=1 ground state of Sm have been obtained for He, Ar, and Xe. Differences in polarization characteristics between the collision-induced Hanle resonances in Na and Sm are pointed out.

Collision-enhanced Hanle resonances and transverse optical pumping in four-wave light mixing in Na vapor.

Collision-enhanced Hanle resonances in the 3 $^{2}S_{1/2}$ electronic ground state of Na atoms have been studied in a phase-conjugate four-wave light-mixing geometry. Narrow resonances in zero magnetic field have been observed at very high inert-buffer-gas pressures, with a width of 21 mG, or less than 10 kHz, full width at half-maximum. The intensity and the width of these resonances has been studied as a function of buffer-gas pressure, of alkali-metal vapor pressure, of detuning from the ${D}_{1}$ and ${D}_{2}$ Na resonances, and of the intensity of the incident light beams. Saturation phenomena and power broadening are observed. The results are explained theoretically in terms of transversely pumped optical gratings. The equivalence of this description with collision-induced coherence gratings in the limit of low light intensities is demonstrated.

Collision-induced Hanle resonances of kilohertz width in phase-conjugate four-wave light mixing.

Hanle resonances for coherent four-wave mixing in the ground state of Na are reported whose intensity increases and whose linewidth decreases with increasing inert buffer gas pressure. In 10-mTorr Na vapor with 4 atm of argon, resonances of less than 35 mG full width at half maximum are observed. The high resolution permits direct observation of the fundamental homogeneous broadening mechanisms for the Zeeman coherences responsible for four-wave mixing.

Collision-induced Hanle resonances in four-wave light mixing

First, some historical comments on the Hanle effect and Kastler-type optical pumping are made. Next the recent history of the phenomenon of collision-induced coherences in optical four-wave light mixing experiments is briefly reviewed New experimental results on collision-enhanced Hanle-type resonances in the 3 2S1/2 ground state configuration of Na atoms in a buffer gas at high pressure are presented. The relationship between these optical fourwave experiments and Kastler-type optical pumping is pointed out.

Two-photon Hanle effect

Two-photon Hanle resonances were observed in a three-level atomic system interacting with two resonant light fields. The choice of suitable polarisation of the light beams and shape analysis of the resonances enabled one to distinguish the effects connected with two-photon coherent transitions from the effects due to stepwise transitions. The experiment was performed with Ne atoms simultaneously interacting with 632.8 nm and 3392 nm radiations from two He-Ne lasers. The mutual coupling of these lasers made it possible to observe the influence of the mutual correlation of both light fields on the two-photon Hanle effect.

Optical bistability from three-level atoms with the use of a coherent nonlinear mechanism

We report on studies on optical bistability from coherently driven $\ensuremath{\Lambda}$-type three-level atoms in a Fabry-Perot resonator. The nonlinear mechanism relies on transverse optical pumping and is due to population trapping in a coherent superposition of the ground-state sublevels. If, under appropriate conditions, a zero-field level-crossing resonance (Hanle resonance) occurs in the atomic system, the optical device is shown to display dispersive or absorptive bistability. Our theoretical studies are based on numerical solutions of the corresponding three-level Bloch equations in the presence of optical feedback. Experiments are performed on the ${D}_{1}$ line in a sodium-filled Fabry-Perot resonator using transverse optical Zeeman pumping of the $^{2}S_{\frac{1}{2}}$ ground state. The measurements are found to be in fair agreement with the theoretical predictions from our simple model.

Excited state dynamics in NO 2: an interpretation of hanle and double resonance experiments

The excited state NO 2 molecule is described as a nonrigid molecule capable of changing between two asymmetric equilibrium configurations. This motion causes a fluctuating orbital angular momentum which is responsible for the discrepancy of lifetime values obtained in Hanle experiments and in radiative decay measurements.

Hanle resonance in radio-frequency fields

Hanle resonance in radio-frequency fields

Quantum statistical theory of optical-resonance phenomena in fluctuating laser fields

A quantum statistical theory of resonant optical phenomena is developed for the case when the fluctuations of the laser, used for exciting transitions, are important. The general equations describing the dynamics of a relaxing two-level atom (TLA) are solved exactly for different types of mean values and the two-time amplitude and intensity correlations. The phase-diffusion model is adopted for laser fluctuations. The exact results are used to analyze the effect of laser fluctuations on a number of optical effects-optical free-induction decay, adiabatic following, the spectrum of the scattered light from a relaxing TLA, the energy-absorption spectrum from a weak field, Hanle resonances, etc. In each case, the laser fluctuations are found to affect in an important way the characteristics of the above optical-resonance phenomena. For example, the spectrum of scattered radiation from a TLA has the usual three-peak structure for fields at resonance and with strengths $\ensuremath{\alpha}$ above the threshold and for $\ensuremath{\alpha}\ensuremath{\gg}{\ensuremath{\gamma}}_{c}$; however, now the peak heights (widths) are in the ratio $3x$ ($\frac{2}{3x}$), $x=\frac{[{\ensuremath{\gamma}}_{c}+\frac{({T}_{1}^{\ensuremath{-}1}+{T}_{2}^{\ensuremath{-}1})}{3}]}{[2{\ensuremath{\gamma}}_{c}+{T}_{2}^{\ensuremath{-}1}]}$, where ${\ensuremath{\gamma}}_{c}^{\ensuremath{-}1}$ is the correlation time for laser phase fluctuations. For ${\ensuremath{\gamma}}_{c}\ensuremath{\gg}\ensuremath{\alpha}$, one gets a single-peak spectrum. The laser field is treated as a second-quantized field with excitation in either a coherent state or a Fock state. The results, obtained by straightforward perturbation theory, but valid for arbitrary values of the relaxation parameters, detuning, and the laser correlation time, are also presented.

Hanle effect, saturation resonances and related phenomena in the presence of two-photon transitions

The optical-pumping cycle in the three-level system e,g,f (Je=1=Jf, Jg=0), irradiated by two monochromatic sigma -polarized laser light waves is analysed theoretically by the successive approximation (iteration) method up to fourth order. The solutions of the density-matrix evolution equations describe (i) in second order, the influence of the Zeeman structure of the e and f states on the saturation resonances in the intermediate level g (second-order population effect) and (ii) in fourth order, the influence of the Hanle effects and the saturation phenomena on the shape of the double-quantum Hanle resonances and on the two-photon transition probabilities.

Hanle resonances for a J=0 to J=1 transition excited by a fluctuating laser beam

The theoretical method developed in a previous paper (see ibid., vol.10, no.2, p.155 (1977)) is applied to the study of the sensitivity of Hanle resonances to the fluctuations of an intense quasi-monochromatic laser beam. The calculations are performed for the simplest possible transition J=0 to or from J=1. Quantitative expressions are derived for the level-crossing signals which appear to be quite perturbed by the fast phase fluctuations.

Nonlinear effects in optical pumping with lasers. II. Possible radiative narrowing of the Hanle resonance at the classical limit

For pt.I see ibid., vol.9, p.357 (1976). A theory of the optical pumping of high-J molecule levels with a broad-band CW laser has previously been developed. The linewidth of the Hanle effect is analysed in the present paper for two particular cases in which an exact integration is possible. These cases are: (i) gT (where g is the Lande factor and T the lifetime) is the same for the two levels; and (ii) one of the Lande factors vanishes. In general, the Hanle resonance is power-broadened for high laser intensities. However, in the case of a zero Lande factor of the ground state, the theory predicts a radiative narrowing of the Hanle effect. It is shown that this most unusual feature is connected to the fact that, in the latter case, the physical observables of the resonance level may get the ground-state lifetime, when the transition is saturated.

Lifetime of the 5s5p1P1 Level of Strontium

The lifetime of the first excited singlet level, 5s5p1P1, of strontium has been measured using the Hanle resonance of the 5s21S0 – 5s5p1P1, 4607 Å, resonance line. The lifetime of the 5s5p1P1 level is 5.29 ± 0.10 ns and the oscillator strength of the 4607 Å line is 1.80 ± 0.03. These results are compared with previous measurements.

Lifetimes and Oscillator Strengths in Atomic Barium

The lifetime of the 5d6p1P1levelatomic barium has been determined from a measurement of the Hanle resonance in the 3501 Å line. The lifetime of this level is 12.17 ± 0.09 × 10−9 s. The lifetimes of a number of levels of atomic barium are collected and absolute oscillator strengths are calculated and compared.

Lifetime of the 6s7p1P1 Level of Barium

The lifetime of the second excited singlet P level of barium 6s7p1P1 has been determined from the width of the Hanle resonance of the 6s7p1P1–6s21S0 3071.58 Å resonance line. The lifetime is determined to be 13.2 ± 0.4 × 10−9 s. From this lifetime the oscillator strength of the 3072 Å transition is 0.12 ± 0.05 and that of the 6s7p1P1–6s5d1D2 4726 Å is 0.09 ± 0.04.