Induced absorption and stimulated emission in a driven two-level atom

1992 ◽  
Vol 70 (6) ◽  
pp. 427-431 ◽  
Author(s):  
Constantine Mavroyannis
Keyword(s):  
Excited State ◽  
Ground State ◽  
Laser Field ◽  
Low Frequency ◽  
Ultrashort Pulses ◽  
Stimulated Emission ◽  
Spectral Lines ◽  
Laser Photon ◽  
Induced Absorption ◽  
Level Atom

We have considered the induced processes that occur in a driven two-level atom, where a laser photon is absorbed and emitted by the ground and by the excited states of the atom, respectively. In the low-intensity limit of the laser field, the induced spectra arising when a laser photon is absorbed by the ground state of the atom consist of two peaks describing induced-absorption and stimulated-emission processes, respectively, where the former prevails over the latter. Asymmetry of the spectral lines occurs at off-resonance and its extent depends on the detuning of the laser field. The physical, process where a laser photon is emitted by the excited state is the reverse of that arising from the absorption of a laser photon by the ground state of the atom. The former differs from the latter in that the emission of a laser photon by the excited state occurs in the low-frequency regime and that the stimulated-emission process prevails over that of the induced absorption. In this case, amplification of ultrashort pulses is likely to occur without the need of population inversion between the optical transitions. The computed spectra are graphically presented and discussed.

Interference spectra in a two-level atom

1990 ◽  
Vol 68 (12) ◽  
pp. 1389-1395 ◽  
Author(s):  
Constantine Mavroyannis
Keyword(s):  
Excited State ◽  
High Intensity ◽  
Laser Field ◽  
Stark Effect ◽  
Ground States ◽  
Spectral Functions ◽  
Laser Photon ◽  
Level Atom ◽  
Dynamic Stark Effect ◽  
Two Peaks

We have considered the interference spectra arising from the competition between a spontaneous process and one induced by a laser field in a two-level atom. Expressions for the spectral functions have been derived describing the spectra of the excited and ground states of the atom in the low- and high-intensity limit of the laser field. For the excited-state spectra in the low-intensity limit, the frequency profiles of the two peaks, which arise from the spontaneous and the induced processes, cancel each other out completely near the center of the line, while for the ground state the induced process dominates. For finite values of the detuning, the spectra of the excited state consist of two peaks, which have positive and negative frequency profiles, respectively. The computed spectra have been graphically presented and discussed. In the high-intensity limit, the dynamic Stark effect dominates the spectra of the excited and ground states of the atom. Expressions for the correlation functions have been derived that describe the emission or the absorption of a laser photon at two different times. The derived expressions for the corresponding delay functions in the low- and high-intensity limits have been found to be identical to those recently proposed in the literature. The laser field has been treated as a classical as well as a quantized entity.

Classical free-electron lasing in an undulating electrostatic field in the axial direction

1992 ◽  
Vol 47 (2) ◽  
pp. 197-217 ◽  
Author(s):  
S. H. Kim
Keyword(s):  
Free Electron ◽  
Free Electron Laser ◽  
Laser Field ◽  
Laser Cavity ◽  
Axial Direction ◽  
Stimulated Emission ◽  
Spectral Lines ◽  
Quantum Mechanical ◽  
Electron Mass ◽  
Fundamental Line

It is shown that the phase of the electromagnetic wave emitted through stimulated emission is intrinsically random. The insensitivity of the phase of the laser field to any disturbance in the laser cavity parameter derives from the fact that stimulated and spontaneous emissions take place concurrently at the same wave vector, the phases of spontaneous emission are mildly bunched, and the central limit theorem can be applied to the phase of the laser field. The two spectral lines observed in the Smith-Purcell free-electron laser experiment show that both classical and quantum-mechanical free-electron lasings, in which the wigglers behave as classical waves and wiggler quanta respectively, take place concurrently at different laser wavelengths in the case of the electric wiggler. It is shown that the coherence of the classical free-electron laser is achieved through modulation of the relativistic electron mass by the electric wiggler. The classical free-electron lasing is calculated using the quantum-augmented classical theory. In this, the probability of stimulated emission is first evaluated by interpreting the classically derived energy exchange between an electron and the laser field from a quantum-mechanical viewpoint. Then the laser gain is obtained from this probability by using a relationship between the two quantities derived by quantum kinetics. The wavelength of the fundamental line of classical free-electron lasing is twice the wavelength of the fundamental line of the free-electron two-quantum Stark emission, which is the quantum free-electron lasing in the electric wiggler. The gain of the classical free-electron lasing appears to scale as λ3w/γ3, where γ is the Lorentz factor of the electron beam and λw is the wavelength of the wiggler.

A laser-excited three-level atom. II numerical results

1990 ◽  
Vol 68 (4-5) ◽  
pp. 411-421 ◽  
Author(s):  
Constantine Mavroyannis
Keyword(s):  
Excited State ◽  
Laser Field ◽  
Spectral Width ◽  
Spectral Functions ◽  
Laser Fields ◽  
Atomic Transitions ◽  
Level Atom ◽  
Short Lifetime ◽  
Strong Transition ◽  
Long Lifetime

Numerical calculations are presented for the interference spectra of a laser-excited three-level atom, where the strong and the weak atomic transitions are driven by resonant and nonresonant laser fields, respectively. The spectral functions describing the interference spectra for the electric dipole allowed excited state have been considered in the low- and high-intensity limit of the laser field operating in the strong transition. The interference spectra arise from the competition between short-lifetime spontaneous processes and short- and long-lifetime excitations induced by the strong and the weak laser fields, respectively. Both laser fields have been treated as quantized and as classical entities. The computed spectra have been presented graphically for different values of the Rabi frequencies and detunings of the weak laser field. It is shown that the decrease in the intensity of the short-lifetime excitation may provide a measure of the spectral width of the long-lifetime excitation.

Adsorbate spectra of rare-gas atoms on metal surfaces

1988 ◽  
Vol 66 (4) ◽  
pp. 741-751 ◽  
Author(s):  
Constantine Mavroyannis
Keyword(s):  
Excited State ◽  
Surface Plasmons ◽  
Metal Surfaces ◽  
Stimulated Emission ◽  
Spectral Lines ◽  
Rare Gas ◽  
Excitation Spectra ◽  
Rare Gas Atoms ◽  
Low Coverage ◽  
Symmetric And Antisymmetric Modes

The optical excitation spectra of neutral rare-gas atoms physisorbed on metal surfaces have been considered. Emphasis has been given to the dynamic effects of the surface plasmons on the lifetimes of the adsorbed atoms. At low coverage and when the damping of the surface plasmons is much greater than the effective radiative damping, the spectral functions of the symmetric and antisymmetric modes consist of asymmetric Lorentzian lines, whose asymmetry depends on the strength of the surface plasmons. At this limit the relative intensities of the symmetric and antisymmetric modes take positive and negative values describing the physical processes of absorption (attenuation) and stimulated emission (amplification), respectively. Hence, the occasional disappearance of the spectral lines of the optical absorption is due to a cancellation process, which takes place between the frequency profiles arising from two nearby excited states of the adsorbed atom. The red shifted peak of the symmetric mode of the higher excited state and the blue shifted peak of the antisymmetric mode of the lower excited state of the atom cancel each other out provided that their frequency profiles nearly coincide. This may be a possible explanation of the persistence-extinction phenomenon that has been observed for a number of rare-gas substrate systems in the low coverage limit, where it has been proposed that a charge-transfer instability exists. Numerical results indicate that the peaks of excited Xe on Al and excited Kr on Au vanish in the low coverage limit.

Optical mixing of frequencies of a strong bichromatic field interacting with a three-level atom. II. Numerical results

1982 ◽  
Vol 60 (2) ◽  
pp. 245-251 ◽  
Author(s):  
Constantine Mavroyannis ◽  
K. J. Woloschuk ◽  
D. A. Hutchinson ◽  
Christine Downie
Keyword(s):  
Ground State ◽  
Laser Field ◽  
Excitation Spectra ◽  
Laser Fields ◽  
Level Atom ◽  
Reduced Frequency ◽  
Spontaneous Emission Probability ◽  
Bichromatic Field ◽  
Optical Mixing ◽  
Selection Of

We have numerically calculated the excitation spectra arising from the 3rd order mixing of the frequencies ωa and ωb of two laser fields interacting with a three-level atom, where each laser field resonantly couples the ground state with each excited state of the atom, respectively. In the limit of high photon densities, the excitation spectra near the reduced frequency X = (ω−ωa + 2ωb)/γ0 ≈ 0 are considered as a function of the reduced Rabi frequencies ηa and ηb of the two laser fields, respectively and γ0 is the spontaneous emission probability. For ηa < ηb the spectra consist of a doublet peaked at [Formula: see text] and its intensity is constant. When ηa = ηb, the spectra are composed of five pairs of bands peaked at [Formula: see text], and [Formula: see text]. When ηa < ηb the computed spectra consist of five pairs of bands, where the intensities of the peaks at [Formula: see text] and [Formula: see text] are positive indicating absorption, those at [Formula: see text] are negative implying amplification, and the two pairs of peaks at [Formula: see text] have positive and negative components describing the mixed process of absorption–amplification. The intensities of these bands are found to vary as (ηa/ηb)2 for (ηa/ηb) > 1 and, therefore, the intensities of the bands are immensely enhanced as the value of the ratio (ηa/ηb) increases. The computed spectra for a wide selection of Rabi frequencies are graphically presented and compared with those derived by analytical methods.

scholarly journals Influence of Giant Nuclear-spin Polarisation on Resonant Gamma-ray Absorption and Emission

1998 ◽  
Vol 51 (2) ◽  
pp. 339
Author(s):  
R. N. Shakhmuratov
Keyword(s):  
Excited State ◽  
Nuclear Spin ◽  
Ground State ◽  
Gamma Ray ◽  
Stimulated Emission ◽  
Laser Pumping ◽  
Nuclear Excited State ◽  
Spin Polarisation ◽  
Subsequent Quenching ◽  
Amplification Without Inversion

We propose a new scheme of gamma-quanta amplification without inversion. Laser pumping of electron states creates giant nuclear-spin polarisation via the hyperfine interaction. This results in extreme cooling of the ground-state nuclear spin in a projection which does not absorb both laser pump and gamma-quanta according to selection rules for these transitions. Induced emission from the nuclear excited state is not influenced by the pump. Therefore gamma-quanta travelling inside the pump beam have an opportunity to induce stimulated emission without subsequent quenching by ground state nuclei.

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