We have investigated three resonant nonlinear processes in atomic cesium vapor. They are third harmonic generation, two photon absorption, and parametric frequency conversion. Resonant enhancement of each is provided by tuning the ruby laser half the 6S - 9D transition frequency of 28828.90 cm. The parametric process involves, in addition, a resonance with one of the P states. We have studied the variation of each of the three processes with laser intensity and frequency. At exact resonance the THG is found to be proportional to the square of the laser intensity and the TPA is proportional to laser intensity over a large power range. The resonance lineshape for both processes is found to be power dependent. A detailed analysis of these two processes based on steady state density matrix calculations and including A. C. Stark shifts, photoionization, and beam geometry is shown to accurately describe most of our observations.
We have investigated three resonant nonlinear processes in atomic cesium vapor. They are third harmonic generation, two photon absorption, and parametric frequency conversion. Resonant enhancement of each is provided by tuning the ruby laser half the 6S - 9D transition frequency of 28828.90 cm. The parametric process involves, in addition, a resonance with one of the P states. We have studied the variation of each of the three processes with laser intensity and frequency. At exact resonance the THG is found to be proportional to the square of the laser intensity and the TPA is proportional to laser intensity over a large power range. The resonance lineshape for both processes is found to be power dependent. A detailed analysis of these two processes based on steady state density matrix calculations and including A. C. Stark shifts, photoionization, and beam geometry is shown to accurately describe most of our observations.
This thesis describes three experiments performed in gases. Chapter 2 describes the first observation of four wave degenerate mixing in cesium vapor. Its basis in nonlinear optics is explained and a simple set of equations are derived which predict the resonant behavior, density dependence, and the power dependence of the signal. Experimental results are then compared to those predicted and reasonable agreement is obtained. A value of (chi)(,zxxz) is measured as (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) compared to the value calculated of 2.8(.)10('-30) esu/atom. The agreement is satisfactory considering the competing processes involved such as photoionization, two-photon absorption, etc. which would tend to reduce the signal observed. The experimental difficulties encountered, i.e., large background and absorption of the laser, limit the usefulness of the process as a probe of the nonlinear optics of cesium. In the third chapter, results are given for measurements of inelastic scattering cross-sections for the 9D and 10D states of cesium. The cross-sections measured (in units of 10('-13)cm('2)) for the fine structure-changing collisions (sigma)(,21) Cs(n('2)D(,5/2)) + Cs(6('2)S(,1/2)) Cs(n('2)D(,3/2)) + Cs(6('2)S(,1/2)) (sigma)(,12) for n = 9 and n = 10 are 1.50 (+OR-) 0.3 and 2.01 (+OR-) 0.4, for (sigma)(,t1) respectively. The cross sections for nonradiative relaxation (sigma)(,t2) Cs(n('2)D(,5/2)) + Cs(6('2)S(,1/2)) out of D states (sigma)(,t1) Cs(n('2)D(,3/2) )+(, )Cs(6('2)S(,1/2)) out of D states for n = 9 and n = 10 are 0.66 (+OR-) 0.3 and 1.4 (+OR-) 0.4 for (sigma)(,t1) and 1.1 (+OR-) 0.4 and 1.7 (+OR-) 0.4 for (sigma)(,t2), respectively. The cross-sections agree well with previously measured values, where available, and represented the first experimental verification that the cross-sections (sigma)(,t1) and (sigma)(,t2) are the same within our experimental uncertainties. In chapter 4 we report the observation of cancellation of rotational e-fects in the intensity of ultraviolet b and s of OH. The b and oscillator strength for transition in the (1,0) b and of OH has been measured and found to be independent of rotational excitation. This independence is explained in terms of the cancellation of a rotationally induced increase in the Franck-Condon factor by an equivalent decrease in the electronic transition moment. We have also remeasured the (0,0) b and oscillator strength as a function of rotational energy and obtained a value for (rho) = 0.75 (+OR-) 0.02A('-1). This value is used along with spectroscopic data to fit a simple model for explaining rotationally induced effects. Very good agreement is found with our data and previous calculations.
The present paper applies the method of high-intensity quantum electrodynamics developed earlier to several problems of current experimental interest. In this paper the intensitydependent shifts and widths of atomic levels are calculated and applied to a given transition near resonance. The technique is demonstrated with three examples: the multiphoton ionization of atomic cesium and hydrogen in atomic beams and third-harmonic production in an atomic vapor. It is found that the multiphoton-ionization rate in a relatively weak laser beam (of order 108 W/cm2) is determined by the intensity-dependent level width (6f configuration) as well as the interference of the fine-structure states, and that the rates for hydrogen, in a much more intense beam (of order 1012 W/cm2) are determined by both the intensity-dependent widths and shifts as‘ well as the wave-function renormalization constants. The agreement of these two examples of calculations with the experiments done recently is satisfactory. For third-harmonic production the role of two-photon resonance is emphasized, and the dependence of the generated third-harmonic intensity on the intensity and frequency of the fundamental is discussed. Near resonance, the ratio of third-harmonic intensity to fundamental intensity saturates.
The density-matrix formalism is used to develop the theory of two-photon-resonant third-harmonic generation in metal vapors taking into account saturation, ionization, laser-induced Stark shifts, and variations in the wave-vector mismatch as a result of population redistribution. It is shown that for third-harmonic generation in the ultraviolet and the vacuum-ultraviolet regions, where $3\ensuremath{\omega}$ exceeds the ionization limit of the metal vapor, two-photon-resonant three-photon ionization will be the main limiting process. This will also be true for four-wave parametric processes. For efficient energy conversion, the two-photon-resonant metal vapor must be phase matchable to allow large vapor density and cell length. Otherwise, the low incident intensity limits, set by the saturation and the ionization effects, cannot be efficiently converted in only one coherence length. The theory is applied to two-photon-resonant tripling of the ruby laser in cesium vapor.
This work reports the multiphoton ionization of cesium atoms, via resonance with the 6F level, by interaction with a single transverse and longitudinal mode neodymium-glass laser beam. At a low rate of ion production, when the laser frequency is tuned through resonance, the laser intensity necessary to create a constant number of ions passes through a minimum, as expected, for a three-photon energy equal to the unperturbed $6S\ensuremath{\rightarrow}6F$ transition energy. But for a higher ionization rate, involving larger laser intensities, a departure from expectation is observed which is interpreted as a consequence of an energy shift of the transition. The level shifts are demonstrated in another way by their strong effect on the experimental order of nonlinearity of the interaction, Kexpt. A sharp variation of Kexpt is observed when the energy shift of the $6S\ensuremath{\rightarrow}6F$ transition exactly compensates the wavelength detuning of the laser. The latter method gives shift values which are found to be independent of the large variations of the interaction volume under conditions of resonance. Both methods give a linear dependence of the shifts on the laser intensity. Identification of these shifts with energy shifts of the $6S\ensuremath{\rightarrow}6F$ transition is subject to theoretical reservations and needs further experimentation.
We present nonlinear spectra of four-level ladder cesium atoms employing 6S 1/2 → 6P 3/2→ 7S 1/2 → 30P 3/2 scheme of a room temperature vapor cell. A coupling laser drives Rydberg transition, a dressing laser couples two intermediate levels, and a probe laser optically probes the nonlinear spectra via electromagnetically induced transparency (EIT). Nonlinear spectra are detected as a function of coupling laser frequency. The observed spectra exhibit an enhanced absorption (EA) signal at coupling laser resonance to Rydberg transition and enhanced transmission (ET) signals at detunings to the transition. We define the enhanced absorption (transmission) strength, H EA (H ET), and distance between two ET peaks, γ ET, to describe the spectral feature of the four-level atoms. The enhanced absorption signal H EA is found to have a maximum value when we vary the dressing laser Rabi frequency Ω d, corresponding Rabi frequency is defined as a separatrix point, Ω dSe . The values of Ω dSe and further η = Ω dSe /Ω c are found to depend on the probe and coupling Rabi frequency but not the atomic density. Based on Ω dSe , the spectra can be separated into two regimes, weak and strong dressing ranges, Ω d ≲ Ω dSe and Ω d ≳ Ω dSe , respectively. The spectroscopies display different features at these two regimes. A four-level theoretical model is developed that agrees well with the experimental results in terms of the probe-beam absorption behavior of Rabi frequency-dependent dressed states.
The probability of a two-photon absorption (TPA) process is quantified by means of the TPA cross-section. In this work the TPA cross-section for the 6 S 1/2 → 8 S 1/2 transition in cesium (Cs) atoms is obtained from a theoretical and experimental approach. It is calculated using second order perturbation theory including hyperfine structure and Doppler broadening for a thermal atomic vapor. The theoretical values for the TPA cross-sections of the two allowed hyperfine transitions are σ ~ 3,3 =3.10×10 −24 cm 4 /W and σ ~ 4,4 =3.65×10 −24 cm 4 /W. An experiment is set up to measure these cross-sections based on the quadratic dependence between the TPA transition rate and the intensity of the laser light. Values of σ ~ 3,3 =(3.6±1.1)×10 −24 cm 4 /W and σ ~ 4,4 =(4.6±1.1)×10 −24 cm 4 /W are obtained from the measurements. The results show an agreement between theory and experiment. To the best of our knowledge, this is the first time that these cross-sections are reported.