Spontaneous emission of radiation

2021 ◽  
pp. 417-454
Author(s):  
Geoffrey Brooker
Keyword(s):  
Spontaneous Emission ◽  
Line Profile ◽  
High Frequency ◽  
Quantum Electrodynamics ◽  
Golden Rule ◽  
Dipole Emission ◽  
Radiation Induced ◽  
Rule Number ◽  
Spectral Line Profile ◽  
Elliptically Polarized

“Spontaneous emission of radiation” calculates the rate of spontaneous electric-dipole emission of a photon by an excited atom or molecule. The calculation proceeds by using basic quantum mechanics (i.e. not using the short cuts of Chapter 19); it uses quantum electrodynamics but is not, on that account, particularly difficult. A 2p–1s transition in hydrogen is used as exemplar; the radiation is elliptically polarized. The spectral line profile (lineshape function) is approximately Lorentzian, but has a high-frequency cut-off, needed to prevent the power radiated from diverging. A radiation-induced frequency shift is negligible. The width of the line profile agrees with the Einstein A-coefficient. A high-frequency cut-off is shown to apply similarly in the derivation of Golden Rule Number Two.

The Einstein A and B coefficients

2021 ◽  
pp. 228-240
Author(s):  
Geoffrey Brooker
Keyword(s):  
Spontaneous Emission ◽  
Line Profile ◽  
Quantum Electrodynamics ◽  
Detailed Balance ◽  
Stimulated Emission ◽  
Spectral Lineshape ◽  
Single Field ◽  
Atomic States ◽  
B Coefficients ◽  
Lineshape Function

The Einstein A and B coefficients for atom–photon reactions are defined: they describe absorption, stimulated emission, and spontaneous emission. We calculate B and consequently find A by the Einstein trick. The procedure is validated by application of detailed balance. Separating out frequencies permits introduction of the spectral lineshape function (normalized line profile). A reformulation describes transitions involving single atomic states and single field modes. This points to a link with quantum electrodynamics.

scholarly journals Measuring and characterizing the line profile of HARPS with a laser frequency comb

2020 ◽  
Vol 645 ◽  
pp. A23
Author(s):  
F. Zhao ◽  
G. Lo Curto ◽  
L. Pasquini ◽  
J. I. González Hernández ◽  
J. R. De Medeiros ◽  
...  
Keyword(s):  
Line Profile ◽  
Frequency Comb ◽  
Laser Frequency ◽  
Line Intensities ◽  
Measured Position ◽  
Wavelength Scale ◽  
Spectral Line Profile ◽  
The Stability ◽  
A Charge

Aims. We study the 2D spectral line profile of the High Accuracy Radial Velocity Planet Searcher (HARPS), measuring its variation with position across the detector and with changing line intensity. The characterization of the line profile and its variations are important for achieving the precision of the wavelength scales of 10−10 or 3.0 cm s−1 necessary to detect Earth-twins in the habitable zone around solar-like stars. Methods. We used a laser frequency comb (LFC) with unresolved and unblended lines to probe the instrument line profile. We injected the LFC light – attenuated by various neutral density filters – into both the object and the reference fibres of HARPS, and we studied the variations of the line profiles with the line intensities. We applied moment analysis to measure the line positions, widths, and skewness as well as to characterize the line profile distortions induced by the spectrograph and detectors. Based on this, we established a model to correct for point spread function distortions by tracking the beam profiles in both fibres. Results. We demonstrate that the line profile varies with the position on the detector and as a function of line intensities. This is consistent with a charge transfer inefficiency effect on the HARPS detector. The estimate of the line position depends critically on the line profile, and therefore a change in the line amplitude effectively changes the measured position of the lines, affecting the stability of the wavelength scale of the instrument. We deduce and apply the correcting functions to re-calibrate and mitigate this effect, reducing it to a level consistent with photon noise.

Stark Broadening Spectral Line Profile at Different Electric Microfield Distribution Functions

2009 ◽  
Vol 29 (2) ◽  
pp. 529-532
Author(s):  
冉俊霞 Ran Junxia ◽  
张少朋 Zhang Shaopeng ◽  
李红莲 Li Honglian ◽  
郝晓辉 Hao Xiaohui ◽  
庞学霞 Pang Xuexia
Keyword(s):  
Spectral Line ◽  
Line Profile ◽  
Distribution Functions ◽  
Stark Broadening ◽  
Spectral Line Profile

Role of Spectral Line Profile in Laser IR Analysis of Multicomponent Gas Mixtures

2019 ◽  
Vol 13 (5) ◽  
pp. 727-738
Author(s):  
Sh. Sh. Nabiev ◽  
S. V. Ivanov ◽  
A. S. Lagutin ◽  
L. A. Palkina ◽  
S. V. Malashevich ◽  
...  
Keyword(s):  
Spectral Line ◽  
Line Profile ◽  
Gas Mixtures ◽  
Multicomponent Gas ◽  
Spectral Line Profile ◽  
Ir Analysis

scholarly journals Measurement of line profiles

1986 ◽  
Vol 118 ◽  
pp. 401-412
Author(s):  
David F. Gray
Keyword(s):  
Spectral Line ◽  
High Precision ◽  
Line Profile ◽  
Line Profiles ◽  
Spectral Line Profile ◽  
The University

The basic requirements for high precision spectral line profile measurements are reviewed, with the observatory at the University of Western Ontario serving to illustrate several of the points.

scholarly journals Radiation-induced morbidity evaluated by high-frequency ultrasound

2016 ◽  
Vol 55 (12) ◽  
pp. 1498-1500 ◽  
Author(s):  
Line H. Schack ◽  
Jan Alsner ◽  
Jens Overgaard ◽  
Christian Nicolaj Andreassen ◽  
Birgitte V. Offersen
Keyword(s):  
High Frequency ◽  
High Frequency Ultrasound ◽  
Radiation Induced ◽  
Frequency Ultrasound
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