Intergalactic photon density.
Intergalactic photon density estimated based on luminosity function of galaxies
PHOTON DENSITY↗
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On “incorrectnes” of the rate equation for photon density of semiconductor lasers
The authors of works [1, 2] published in Quantum Electronics assert that the rate equation for photon density with a term taking into account the contribution of spontaneous emission to the laser mode is erroneous (i.e., the spontaneous term should be excluded from consideration) and criticise works [3, 4]. In the present work, we analyse previously published papers and show that the necessity of taking into account the contribution of spontaneous emission to the laser mode follows from the quantum-mechanical rate equation for semiconductor lasers. The results obtained in [1, 2] are analysed. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Emission-line variability and the broad-line region of quasi-stellar objects. I - Time scales and photon densities
Spectroscopic data for five low-redshift QSOs taken over several years are presented as evidence for emission-line variability in QSOs. The broad hydrogen emission lines in the QSOs 0026 + 129, 1202 + 281, 1612 + 261, and 2141 + 175 are found to vary in step with their underlying continua. Another QSO, 2135 - 147, shows an increase in the intensities of its hydrogen lines five years after the increase in its continuum level. The inferred upper limit to the size of the broad emission line region is smaller than 3 lt-yr, probably as small as 0.4 lt-yr for 0026 + 129, if the line-emitting region is spherically distributed. Such a small size implies a very high density of ionizing photons, of the order of 10 to the 10th/cu cm. A very high nucleon density must then be assumed in order to obtain a value of the ionization parameter consistent with current photoionization models.
Zheng, Wei↗
A Determination of the Intergalactic Redshift Dependent UV-Optical-NIR Photon Density Using Deep Galaxy Survey Data and the Gamma-Ray Opacity of the Universe
We calculate the intensity and photon spectrum of the intergalactic background light (IBL) as a function of red shift using an approach based on observational data obtained at in different wavelength bands from local to deep galaxy surveys. Our empirically based approach allows us, for the firs.t time, to obtain a completely model independent determination of the IBL and to quantify its uncertainties. Using our results on the IBL, we then place upper and lower limits on the opacity of the universe to gamma-rays, independent of previous constraints.
Stecker, Floyd W.↗
A Determination of the Intergalactic Redshift Dependent UV-Optical-NIR Photon Density Using Deep Galaxy Survey Data and the Gamma-ray Opacity of the Universe
We calculate the intensity and photon spectrum of the intergalactic background light (IBL) as a function of redshift using an approach based on observational data obtained in many different wavelength bands from local to deep galaxy surveys. This allows us to obtain an empirical determination of the IBL and to quantify its observationally based uncertainties. Using our results on the IBL, we then place 68% confidence upper and lower limits on the opacity of the universe to gamma-rays, free of the theoretical assumptions that were needed for past calculations. We compare our results with measurements of the extragalactic background light and upper limits obtained from observations made by the Fermi Gamma-ray Space Telescope.
Stecker, Floyd W.↗
Diffuse Gamma-Ray Emission from the Starburst Galaxy NGC 253
The starburst galaxy NGC 253 was observed with the Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory (CGRO) satellite. We obtain a 2 sigma upper limit to the gamma-ray emission above 100 MeV of 8 x 10(exp -8) photons/sq cm/s. Because of their large gas column densities and supernova rates, nearby starburst galaxies were predicted to have gamma-ray fluxes detectable by EGRET. Our nondetection of gamma-rays from NGC 253 motivates us to reexamine in detail the premise of supernova acceleration of cosmic rays and the effect of enhanced cloud densities, photon densities, and magnetic fields on the high-energy spectra of galaxies. By modeling the expected gamma-ray and synchrotron spectra from NGC 253, we find that up to 20% of the energy from supernovae is transferred to cosmic rays in the starburst, which is consistent with supernova acceleration models. Our calculations match the EGRET and radio data well with a supernova rate of 0.08/yr, a magnetic field B greater than or approximately equal to 5 x 10(exp -5) G, a density n approximately 300/cu cm, a photon density U(sub ph) approximately 200 eV/cu cm, and an escape timescale tau(sub o) less than or approximately equal to 10 Myr.
Bertsch, David L.↗
Rate equations analysis of phase-locked semiconductor laser arrays under steady state conditions
Rate equations analysis of phase-locked semiconductor laser arrays has been carried out. It was found that for given (laser) current densities, the photon density distribution in the array elements is that particular one which maximizes the total photon density. The results of this analysis were then combined with the waveguide properties of the laser array waveguide, yielding a basic model of phase-locked diode laser arrays. This model explains the effects of the variation of the current combination through the array elements on its mode structure that were observed recently.
Katz, J.↗
Non-Wiener Dynamics of Open Systems for Nonzero Number Density of Surrounding Photons
We propose a collective decay model for a localized ensemble of identical atoms in a vacuum broadband electromagnetic field with a nonzero photon number density considering second-order terms in the atom–field interaction constant. The model is based on the stochastic differential equation for the evolution operator for the atomic ensemble and surroundings, which is controlled by the main quantum random processes and independent classical Wiener processes. It is shown that in some cases, nonzero photon number density does not influence the suppression of collective emission of atoms, and its existence is manifested as an additional mechanism of redistribution of atoms over collective sublevels.
74 ATOMIC AND MOLECULAR PHYSICS↗
Extragalactic Backgrounds in the Far UV and Exploring Star Formation at High Redshifts with Gamma-ray Observations
The determination of the intergalactic photon densities from the FIR to the UV which is produced by stellar emission and dust reradiation at various redshifts can provide an independent measure of the star formation history of the universe. Using recent Spitzer and GALEX data in conjunction with other observational inputs, Stecker, Malkan and Scully have calculated the intergalactic photon density as a function of both energy and redshift for 0 < zeta < 6 for photon energies from 0.003 eV to the Lyman limit cutoff at 13.6 eV in a ACDM universe with Omega(sub Lambda) = 0.7 and Omega(sub m) = 0.3. Their results are based on backwards evolution models for galaxies which were developed by Malkan and Stecker previously. The calculated background SEDs at zeta = 0 are in good agreement with the present observational data and limits. The calculated intergalactic photon densities as a function of redshift were used to predict to extend the absorption of high energy 7-rays in intergalactic space from sources such as blazars and quasars, this absorption being produced by interactions the y-rays with the intergalactic FIR-UV photons having the calculated densities. The results are in excellent agreement with absorption features found in the low gamma-ray spectra of Mkn 421, Mkn 501 at, zeta = 0.03 and PKS
Stecker, Floyd W.↗
An analytical model for vertical dual-cavity quantum-dot optical amplifiers
Novel closed-form model for the threshold conditions and the optical gains of vertical dual-cavity semiconductor optical amplifier (VDC-SOA) is derived. Expressions for the transfer functions that relate the average photon density inside the two cavities to the incident photon density are derived. The model is simple, accurate and easy to use for designing dual-wavelength laser amplifiers. Good agreement is obtained between the analytical model and numerical calculations. The transmitted and reflective bistability characteristics of quantum dot VDC-SOA have been investigated. The threshold condition of each mode is expressed in terms of the top-cavity and the bottom-cavity currents. The dual modes λ{sub o}{sup +} and λ{sub o}{sup −} show different bistability behavior as a function of the top cavity current when the device operates at fixed operating point below the threshold curve. We find that the contrast ratio of mode λ{sub o}{sup +} is a weak function of the device currents, and the hysteresis width increases when the top cavity current is increased. For mode λ{sub o}{sup −} large contrast ratio and hysteresis width are obtained when the two cavities exhibit equal currents. Our analysis also reveals that the spectral characteristics of mode λ{sub o}{sup +} are different from that of mode λ{sub o}{sup −}.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Intergalactic Photon Spectra from the Far-IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the Universe to High-Energy Gamma Rays
We calculate the intergalactic photon density as a function of both energy and redshift for 0<z<6 for photon energies from.003 eV to the Lyman limit cutoff at 13.6 eV in a (Omega)CDM universe with (Omega)(Lambda)=0.7 and (Omega)m=0.3. The basic features of our backward-evolution model for galaxies were developed in earlier papers by Malkan & Stecker. With a few improvements, we find that this evolutionary model gives predictions of new deep number counts from Spitzer, as well as a calculation of the spectral energy distribution of the diffuse infrared background, which are in good agreement with the data. We then use our calculated intergalactic photon densities to extend previous work on the absorption of high-energy Gamma-rays in intergalactic space owing to interactions with low-energy photons and the 2.7 K cosmic microwave background radiation. We calculate the optical depth of the universe, Tau , for Gamma-rays having energies from 4 GeV to 100 TeV emitted by sources at redshifts from 0 to 5. We also give an analytic fit with numerical coefficients for approximating (E(Gamma), z). As an example of the application of our results, we calculate the absorbed spectrum of the blazar PKS 2155-304 at z=0.117 and compare it with the spectrum observed by the HESS air Cerenkov Gamma-ray telescope array.
Stecker, F. W.↗
Mode selection and frequency tuning by injection in pulsed TEA-CO2 lasers
An analytical model characterizing pulsed-TEA-CO2-laser injection locking by tunable CW-laser radiation is presented and used to explore the requirements for SLM pulse generation. Photon-density-rate equations describing the laser mechanism are analyzed in terms of the mode competition between photon densities emitted at two frequencies. The expression derived for pulsed dye lasers is extended to homogeneously broadened CO2 lasers, and locking time is defined as a function of laser parameters. The extent to which injected radiation can be detuned from the CO2 line center and continue to produce SLM pulses is investigated experimentally in terms of the analytical framework. The dependence of locking time on the detuning/pressure-broadened-halfwidth ratio is seen as important for spectroscopic applications requiring tuning within the TEA-laser line-gain bandwidth.
Flamant, P. H.↗
Design Fabrication and Characterization of High Density Silicon Photonic Components
Our burgeoning appetite for data relentlessly demands exponential scaling of computing and communications resources leading to an overbearing and ever-present drive to improve e ciency while reducing on-chip area even as photonic components expand to ll application spaces no longer satis ed by their electronic counterparts. With a high index contrast, low optical loss, and compatibility with the CMOS fabrication infrastructure, silicon-on-insulator technology delivers a mechanism by which e cient, sub-micron waveguides can be fabricated while enabling monolithic integration of photonic components and their associated electronic infrastructure. The result is a solution leveraging the superior bandwidth of optical signaling on a platform capable of delivering the optical analogue to Moore's Law scaling of transistor density. Device size is expected to end Moore's Law scaling in photonics as Maxwell's equations limit the extent to which this parameter may be reduced. The focus of the work presented here surrounds photonic device miniaturization and the development of 3D optical interconnects as approaches to optimize performance in densely integrated optical interconnects. In this dissertation, several technological barriers inhibiting widespread adoption of photonics in data communications and telecommunications are explored. First, examination of loss and crosstalk performance in silicon nitride over SOI waveguide crossings yields insight into the feasibility of 3D optical interconnects with the rst experimental analysis of such a structure presented herein. A novel measurement platform utilizing a modi ed racetrack resonator is then presented enabling extraction of insertion loss data for highly e cient structures while requiring minimal on-chip area. Finally, pioneering work in understanding the statistical nature of doublet formation in microphotonic resonators is delivered with the resulting impact on resonant device design detailed.
36 MATERIALS SCIENCE↗
Galactic gamma rays produced by Compton scattering of cosmic ray electrons
Previous models of the Compton scattering of the galactic gamma rays have been based on starlight distributions determined from galactic mass models and a constant luminosity per unit mass. The fact that the spiral arms have a significantly higher photon density than does the base disk containing the bulk of the galactic mass has been neglected in calculating the Compton gamma-ray component. The inclusion of the spiral arm Compton component produces enhanced gamma-ray intensities along tangents to spiral arms. Irrespective of whether the cosmic-ray electron density is enhanced in the spiral arms, increased gamma-ray emission is produced along the spiral arm tangents due to increased photon density. Thus, cosmic ray sources are not necessarily located in the arms.
Higdon, J. C.↗
Polariton-Type Dispersion Laws for Three-Level Atoms Interacting with Two Laser Radiation Pulses
Behavioral features of polariton dispersion laws are studied for three-level atoms interacting with two coherent laser radiation pulses with frequencies ω{sub 1} and ω{sub 2} that are in resonance with optically resolved one-photon transitions between levels 1⇆2 and 2⇆3, respectively, and with regard to the direct two-photon transition between levels 1 and 3. The approximation of given photon densities of both pulses compared with the densities of atoms is used. It is shown that the dispersion law consists of three branches whose position and shape are determined by the Rabi frequencies of the above three optical transitions and the photon densities in both pulses. The direct consideration of all three optical transitions leads to the dependence of the dispersion law of atomic polaritons on a new quantum parameter—the phase difference between the three Rabi frequencies. The values of the system parameters are found for which the branches of the dispersion law may intersect. The concept of the surface of the dispersion law is introduced in the dependence of the eigenfrequencies of atomic polaritons on the photon wave vectors in both pulses.
74 ATOMIC AND MOLECULAR PHYSICS↗
Lyα emitter galaxies at z ∼ 2.8 in the extended Chandra Deep Field South. I. Tracing the large-scale structure via Lyα imaging
We present a narrowband survey with three adjacent filters for z = 2.8–2.9 Lyman alpha (Lyα) emitter (LAE) galaxies in the Extended Chandra Deep Field South (ECDFS), along with spectroscopic follow-up. With a complete sample of 96 LAE candidates in the narrowband NB466, we confirm the large-scale structure at z ∼ 2.8 suggested by previous spectroscopic surveys. Compared to the blank field detected with the other two narrowband filters NB470 and NB475, the LAE-density excess in NB466 (900 arcmin{sup 2}) is ∼ 6.0 ± 0.8 times the standard deviation expected at z ∼ 2.8, assuming a linear bias of 2. The overdense large-scale structure in NB466 can be decomposed into four protoclusters, whose overdensities (each within an equivalent comoving volume 15{sup 3} Mpc{sup 3}) relative to the blank field (NB470+NB475) are in the range of 4.6–6.6. These four protoclusters are expected to evolve into a Coma-like cluster (M ≥ 10{sup 15} M {sub ⊙}) at z ∼ 0. We also investigate the various properties of LAEs at z = 2.8–2.9 and their dependence on the environment. The average star formation rates derived from the Lyα, rest-frame UV, and X-ray bands are ∼4, 10, and <16 M {sub ⊙} yr{sup −1}, respectively, implying a Lyα escape fraction of 25% ≲ f{sub ESC}{sup Lyα} ≲ 40% and a UV continuum escape fraction of f{sub ESC}{sup UV,cont} ≳ 62% for LAEs at z ∼ 2.8. The Lyα photon density calculated from the integrated Lyα luminosity function in the overdense field (NB466) is ∼50% higher than that in the blank field (NB470+NB475), and more bright LAEs are found in the overdense field. The three brightest LAEs, including a quasar at z = 2.81, are all detected in the X-ray band and in NB466. These three LAE-active galactic nuclei contribute an extra 20%–30% Lyα photon density compared to other LAE galaxies. Furthermore, we find that LAEs in overdense regions have larger equivalent width values, bluer U − B and V − R (∼2–3σ) colors compared with those in lower density regions, indicating that LAEs in overdense regions are younger and possible less dusty. We conclude that the structure at z ∼ 2.8 in the ECDFS field is a very significant and rare density peak similar to the SSA22 protocluster, and narrowband imaging is an efficient method of detecting and studying such structures in the high-z universe.
79 ASTRONOMY AND ASTROPHYSICS↗
A correlation between hard gamma-ray sources and cosmic voids along the line of sight
We estimate the galaxy density along lines of sight to hard extragalactic gamma-ray sources by correlating source positions on the sky with a void catalog based on the Sloan Digital Sky Survey (SDSS). Extragalactic gamma-ray sources that are detected at very high energy (VHE; E > 100 GeV) or have been highlighted as VHE-emitting candidates in the Fermi Large Area Telescope hard source catalog (together referred to as “VHE-like” sources) are distributed along underdense lines of sight at the 2.4σ level. There is a less suggestive correlation for the Fermi hard source population (1.7σ). A correlation between 10-500 GeV flux and underdense fraction along the line of sight for VHE-like and Fermi hard sources is found at 2.4σ and 2.6σ, calculated from the Pearson correlation coefficients of r = 0.57 and 0.47, respectively. The preference for underdense sight lines is not displayed by gamma-ray emitting galaxies within the second Fermi catalog, containing sources detected above 100 MeV, or the SDSS DR7 quasar catalog. We investigate whether this marginal correlation might be a result of lower extragalactic background light (EBL) photon density within the underdense regions and find that, even in the most extreme case of a entirely underdense sight line, the EBL photon density is only 2% less than the nominal EBL density. Translating this into gamma-ray attenuation along the line of sight for a highly attenuated source with opacity τ(E, z) ~ 5, we estimate that the attentuation of gamma-rays decreases no more than 10%. This decrease, although non-neglible, is unable to account for the apparent hard source correlation with underdense lines of sight.
79 ASTRONOMY AND ASTROPHYSICS↗
Harnessing the photonic local density of states in graphene moiré superlattices
In this work we investigate the electromagnetic local density of states (LDOS) near a twisted bilayer graphene (TBG) deposited over a general isotropic substrate. The band structure of the TBG is calculated within a tight-binding framework, and then used to determine the TBG's conductivity. The latter presents a nontrivial dependence upon the angle of twist, which shows up in the LDOS, allowing for a moiré pattern-dependent quantum emission. For some specific twist angles we show that it is possible to either enhance or decrease the LDOS by an order of magnitude at selected frequencies when compared to the monolayer. Furthermore, this impressive variation is explained in terms of the presence/absence of well defined surface plasmon polaritons (SPPs). Altogether our findings demonstrate that TBG is an alternative, versatile material platform for controlling spontaneous emission and enhancing light-matter interactions, and pave the way for further studies and applications of quantum emission in the emerging class of two-dimensional moiré materials.
36 MATERIALS SCIENCE↗