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Three Laser Experiments in Gases.

Michael Toubert Myers

Published Jan 1, 1981• 0 citations
OpenAlex

Abstract

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.

Related papers

Three Resonant Nonlinear Optical Processes In Atomic Cesium.

Arlee V. Smith

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.

•Jan 1, 1977•0 citations

Inelastic collisions between excited alkali atoms and molecules. IV. Sensitized fluorescence and quenching in mixtures of cesium with N2, H2, HD, and D2

D. A. McGillis, L. Krause

6 2P1/2 ↔ 6 2P3/2 mixing and 6 2S1/2 ← 6 2P1/2,3/2 quenching in cesium, induced in collisions with ground state N2, H2, HD, and D2 molecules, have been investigated using techniques of sensitized fluorescence. Mixtures of cesium vapor and the gases, in which the cesium vapor pressure was kept very low to avoid multiple scattering, were irradiated with each component of the cesium resonance doublet in turn. The fluorescence which contained both components of the doublet was observed in a direction perpendicular to that of the exciting beam. Measurements of the relative intensities of the fluorescent components yielded the following cross sections for mixing and quenching. For Cs–N2 collisions: Q12(2P1/2 → 2P3/2) = 4.7 Å2, Q21(2P1/2 ← 2P3/2) = 25 Å2, Q10(2S1/2 ← 2P1/2) = 77 Å2, Q20(2S1/2 ← 2P3/2) = 69 Å2. For Cs–H2 collisions: Q12 = 6.7 Å2, Q21 = 44 Å2, Q10 = 7 Å2, Q20 = 5 Å2. For Cs–HD collisions: Q12 = 4.8 Å2, Q21 = 32 Å2, Q10 = 4 Å2, Q20 = 3 Å2. For Cs–D2 collisions: Q12 = 4.2 Å2, Q21 = 28 Å2, Q10 = 8 Å2, Q20 = 7 Å2. The Cs–N2 and Cs–H2 cross sections supersede the values published previously (McGillis and Krause 1967). The cross sections Q21 appear to exhibit resonances with molecular rotational transitions.

Canadian Journal of Physics•May 1, 1968•36 citations

Theoretical and experimental study of the 6S-8S two-photon absorption cross-section in cesium atoms

Michael Caracas Núñez, Miguel A. Gonzalez, Mayerlin Núñez Portela

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.

Optics Express•Aug 14, 2023•4 citations

Coherent four-wave mixing in excited and ionized gas media: four-photon spectrochronography, ellipsometry, and nonlinear-optical imaging of atoms and ions

Aleksei M. Zheltikov, Nikolai I Koroteev

Когерентные четьрехволновые процессы РІ возбужденных Рё ионизованных газовых средах: четырехфотонная спектрохронография, эллипсометрия Рё визуализация пространственного распределения атомов Рё РёРѕРЅРѕРІ, Желтиков Рђ.Рњ., Коротеев Рќ.Р

Uspekhi Fizicheskih Nauk•Jan 1, 1999•23 citations

Mixing and quenching of the Cs 5DJstates induced by collisions with caesium ground-state atoms

Mladen Movre, Cedomil Vadla, Vlasta Horvatić

Applying the cw laser absorption and fluorescence method the cross sections for the fine-structure mixing and quenching of the caesium 5D J states have been measured in pure caesium vapour. Caesium atoms were optically excited to the 5D 5/2 state via the quadrupole-allowed 6S 1/2 →5D 5/2 transition. The ground-state caesium density N 0 , obtained from the absorption at the pumped quadrupole transition, and the fluorescence intensity I 689 of the sensitized 5D 3/2 →6S 1/2 emission were measured simultaneously in the range 3×10 14 cm -3 ⩽ N 0 ⩽1×10 16 cm -3 at constant temperature T = 585 K. It was found that the quantity N 0 2 / I 689 exhibited a parabolic dependence on N 0 , confirming that the quenching of the Cs 5D J states is due to collisions with Cs ground-state atoms, not molecules. The coefficients of the second-order polynomial fitted through the measured data yielded the cross sections σ 5/2→3/2 = (57±19)×10 -16 cm 2 and σ D = (35±10)×10 -16 cm 2 for the Cs 5D J fine-structure mixing and quenching, respectively, due to collisions with caesium ground-state atoms. Using recently calculated Cs*+Cs potentials we performed an analysis which shows good agreement between the measured values and the theoretical predictions.

Journal of Physics B Atomic Molecular and Optical Physics•Jul 27, 2000•3 citations

Collisions and half-collisions with lasers

N. K. Rahman, Carla Guidotti

Merging two subfields, collisions and spectroscopy, this book presents the latest research proposals, innovative experiments and fresh ideas. Topics considered include radiative collision induced electron continuum-continuum scattering; models of laser-induced chemical reactions; experimental studies of laser-induced ionizing collisions; laser photodissociation of Na/sub 2/ + ions produced by laser resonant ionization of Na vapor; steady-state electron-atom collision in a laser field; conditions for the observation of the predicted splitting of the laser assisted electron impact of the differential cross section of atoms; transitions between resonances; some proposals for experiments; above-threshold multiphoton ionization; observability of optical collisions in the frequency and the time domain; laser switched collisions - a diagrammatical approach; polarization of atomic fluorescence excited by molecular photodissociation; multiphoton selective excitation; on the role of chaotic dynamics with many basins of attraction; predissociation in a strong electromagnetic field; theory of double resonance; and coherent excitation of polyatomic molecules up to highly excited vibrational states by laser light.

•Jan 1, 1984•42 citations
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.
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.
6 2P1/2 ↔ 6 2P3/2 mixing and 6 2S1/2 ← 6 2P1/2,3/2 quenching in cesium, induced in collisions with ground state N2, H2, HD, and D2 molecules, have been investigated using techniques of sensitized fluorescence. Mixtures of cesium vapor and the gases, in which the cesium vapor pressure was kept very low to avoid multiple scattering, were irradiated with each component of the cesium resonance doublet in turn. The fluorescence which contained both components of the doublet was observed in a direction perpendicular to that of the exciting beam. Measurements of the relative intensities of the fluorescent components yielded the following cross sections for mixing and quenching. For Cs–N2 collisions: Q12(2P1/2 → 2P3/2) = 4.7 Å2, Q21(2P1/2 ← 2P3/2) = 25 Å2, Q10(2S1/2 ← 2P1/2) = 77 Å2, Q20(2S1/2 ← 2P3/2) = 69 Å2. For Cs–H2 collisions: Q12 = 6.7 Å2, Q21 = 44 Å2, Q10 = 7 Å2, Q20 = 5 Å2. For Cs–HD collisions: Q12 = 4.8 Å2, Q21 = 32 Å2, Q10 = 4 Å2, Q20 = 3 Å2. For Cs–D2 collisions: Q12 = 4.2 Å2, Q21 = 28 Å2, Q10 = 8 Å2, Q20 = 7 Å2. The Cs–N2 and Cs–H2 cross sections supersede the values published previously (McGillis and Krause 1967). The cross sections Q21 appear to exhibit resonances with molecular rotational transitions.
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.
Когерентные четьрехволновые процессы РІ возбужденных Рё ионизованных газовых средах: четырехфотонная спектрохронография, эллипсометрия Рё визуализация пространственного распределения атомов Рё РёРѕРЅРѕРІ, Желтиков Рђ.Рњ., Коротеев Рќ.Р
Applying the cw laser absorption and fluorescence method the cross sections for the fine-structure mixing and quenching of the caesium 5D J states have been measured in pure caesium vapour. Caesium atoms were optically excited to the 5D 5/2 state via the quadrupole-allowed 6S 1/2 →5D 5/2 transition. The ground-state caesium density N 0 , obtained from the absorption at the pumped quadrupole transition, and the fluorescence intensity I 689 of the sensitized 5D 3/2 →6S 1/2 emission were measured simultaneously in the range 3×10 14 cm -3 ⩽ N 0 ⩽1×10 16 cm -3 at constant temperature T = 585 K. It was found that the quantity N 0 2 / I 689 exhibited a parabolic dependence on N 0 , confirming that the quenching of the Cs 5D J states is due to collisions with Cs ground-state atoms, not molecules. The coefficients of the second-order polynomial fitted through the measured data yielded the cross sections σ 5/2→3/2 = (57±19)×10 -16 cm 2 and σ D = (35±10)×10 -16 cm 2 for the Cs 5D J fine-structure mixing and quenching, respectively, due to collisions with caesium ground-state atoms. Using recently calculated Cs*+Cs potentials we performed an analysis which shows good agreement between the measured values and the theoretical predictions.
Merging two subfields, collisions and spectroscopy, this book presents the latest research proposals, innovative experiments and fresh ideas. Topics considered include radiative collision induced electron continuum-continuum scattering; models of laser-induced chemical reactions; experimental studies of laser-induced ionizing collisions; laser photodissociation of Na/sub 2/ + ions produced by laser resonant ionization of Na vapor; steady-state electron-atom collision in a laser field; conditions for the observation of the predicted splitting of the laser assisted electron impact of the differential cross section of atoms; transitions between resonances; some proposals for experiments; above-threshold multiphoton ionization; observability of optical collisions in the frequency and the time domain; laser switched collisions - a diagrammatical approach; polarization of atomic fluorescence excited by molecular photodissociation; multiphoton selective excitation; on the role of chaotic dynamics with many basins of attraction; predissociation in a strong electromagnetic field; theory of double resonance; and coherent excitation of polyatomic molecules up to highly excited vibrational states by laser light.