Absorption Cross Sections Of Molecules Research Articles

Multichromatic quantum superpositions in entangled two-photon absorption spectroscopy

Quantum information science is driving progress in a vast number of scientific and technological areas that cover molecular spectroscopy and matter-light interactions in general. In these fields, the ability to generate quantum mechanically-entangled photons is opening avenues to explore the interaction of molecules with quantum light. This work considers an alternative way of correlating photons by including energy superpositions. We study how the multichromatic quantum superposition, or color superposition of photon-pair states, influences the optical properties of organic chromophores. This work uses electronic structure calculations based on time-dependent density functional theory, and a simple modification of the standard entangled two-photon absorption theory. Our calculations show that it is possible to substantially modify the optical absorption cross section of molecules, where constructive and destructive interferences are computed. The quantum interference effects are more pronounced than the constructive ones. These quantum effects, or related ones, could be observed in quantum spectroscopic experiments where qudit photon states are generated.

Reshaping plasmonic resonances using epsilon-near-zero materials for enhanced infrared vibrational spectroscopy

Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful technique for a label-free identification of molecular species. The low infrared absorption cross sections of molecules are made up for the huge electromagnetic field enhancement provided by the resonant excitation of collective electron oscillations in metallic nanoantennas. Since these surface plasmons are localized at the nanometer scale, a minute amount of materials is detected leading to a weak SEIRA signal. The design of actual plasmonics detectors is a trade-off between the detection of very small volumes of molecules and the signal to noise ratio level. We demonstrate that an epsilon-near-zero (ENZ) material combined with nano-slits lifts this constraint and provides both extreme enhancement factor up to 107 and highly contrasted SEIRA signal for an extremely low amount of material of interest. These results are explained by the modification of the electromagnetic field of the gap plasmon mode sustained by the slits in the presence of the ENZ material. We propose to implement this concept with a semiconductor whose doping level engineering provides a versatile way to scan the whole molecules' fingerprint frequency range.

Effect of pressure broadening on molecular absorption cross sections in exoplanetary atmospheres

Spectroscopic observations of exoplanets are leading to unprecedented constraints on their atmospheric compositions. However, molecular abundances derived from spectra are degenerate with the absorption cross sections which form critical input data in atmospheric models. Therefore, it is important to quantify the uncertainties in molecular cross sections to reliably estimate the uncertainties in derived molecular abundances. However, converting line lists into cross sections via line broadening involves a series of prescriptions for which the uncertainties are not well understood. We investigate and quantify the effects of various factors involved in line broadening in exoplanetary atmospheres - the profile evaluation width, pressure versus thermal broadening, broadening agent, spectral resolution, and completeness of broadening parameters - on molecular absorption cross sections. We use H$_2$O as a case study as it has the most complete absorption line data. For low resolution spectra (R$\lesssim$100) for representative temperatures and pressures (T $\sim$ 500K-3000K, P$\lesssim$1 atm) of H$_2$-rich exoplanetary atmospheres we find the median difference in cross sections ($\delta$) introduced by various aspects of pressure broadening to be $\lesssim$1\%. For medium resolutions (R$\lesssim$5000), including those attainable with JWST, we find that $\delta$ can be up to 40\%. For high resolutions (R$\sim$10$^5$) $\delta$ can be $\gtrsim$100\%, reaching $\gtrsim$1000\% for low temperatures (T$\lesssim$500K) and high pressures (P$\gtrsim$1 atm). The effect is higher still for self broadening. We generate a homogeneous database of absorption cross sections of molecules of relevance to exoplanetary atmospheres for which high temperature line lists are available, particularly H$_2$O, CO, CH$_4$, CO$_2$, HCN, and NH$_3$.

Absolute absorption cross sections from photon recoil in a matter-wave interferometer.

We measure the absolute absorption cross section of molecules using a matter-wave interferometer. A nanostructured density distribution is imprinted onto a dilute molecular beam through quantum interference. As the beam crosses the light field of a probe laser some molecules will absorb a single photon. These absorption events impart a momentum recoil which shifts the position of the molecule relative to the unperturbed beam. Averaging over the shifted and unshifted components within the beam leads to a reduction of the fringe visibility, enabling the absolute absorption cross section to be extracted with high accuracy. This technique is independent of the molecular density, it is minimally invasive and successfully eliminates many problems related to photon cycling, state mixing, photobleaching, photoinduced heating, fragmentation, and ionization. It can therefore be extended to a wide variety of neutral molecules, clusters, and nanoparticles.

The HITRAN 2008 molecular spectroscopic database

This paper describes the status of the 2008 edition of the HITRAN molecular spectroscopic database. The new edition is the first official public release since the 2004 edition, although a number of crucial updates had been made available online since 2004. The HITRAN compilation consists of several components that serve as input for radiative-transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e. spectra in which the individual lines are not resolved; individual line parameters and absorption cross-sections for bands in the ultraviolet; refractive indices of aerosols, tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 42 molecules including many of their isotopologues.

The HITRAN 2004 molecular spectroscopic database

This paper describes the status of the 2004 edition of the HITRAN molecular spectroscopic database. The HITRAN compilation consists of several components that serve as input for radiative transfer calculation codes: individual line parameters for the microwave through visible spectra of molecules in the gas phase; absorption cross-sections for molecules having dense spectral features, i.e., spectra in which the individual lines are unresolvable; individual line parameters and absorption cross-sections for bands in the ultra-violet; refractive indices of aerosols; tables and files of general properties associated with the database; and database management software. The line-by-line portion of the database contains spectroscopic parameters for 39 molecules including many of their isotopologues. The format of the section of the database on individual line parameters of HITRAN has undergone the most extensive enhancement in almost two decades. It now lists the Einstein A -coefficients, statistical weights of the upper and lower levels of the transitions, a better system for the representation of quantum identifications, and enhanced referencing and uncertainty codes. In addition, there is a provision for making corrections to the broadening of line transitions due to line mixing.

Synthesis, Structures, and Properties of Two New Two-Photon Photopolymerization Initiators

Abstract Two new two-photon photopolymerization initiators, diphenyl-(4-{2-[4-(2-pyridin-4-ylvinyl)phenyl]vinyl}phenyl)amine 3 and 9-(4-{2-[4-(2-pyridin-4-ylvinyl)phenyl]vinyl}phenyl)-9H-carbazole 4, have been synthesized and their crystal structures have been determined. One-photon fluorescence, one-photon fluorescence quantum yields, one-photon fluorescence lifetimes, and two-photon fluorescence have been investigated. The results show that they are good two-photon absorbing chromophores and effective two-photon photopolymerization initiators. The calculated two-photon absorption cross sections of molecules 3 and 4 for the lowest excited state are 59.3 × 10−50 and 43.0 × 10−50 cm4 s photon−1, respectively. Two-photon initiating polymerization microfabrication experiments have been studied and the possible photopolymerization mechanisms have been discussed.

The HITRAN molecular spectroscopic database: edition of 2000 including updates through 2001

This paper describes the status circa 2001, of the HITRAN compilation that comprises the public edition available through 2001. The HITRAN compilation consists of several components useful for radiative transfer calculation codes: high-resolution spectroscopic parameters of molecules in the gas phase, absorption cross-sections for molecules with very dense spectral features, aerosol refractive indices, ultraviolet line-by-line parameters and absorption cross-sections, and associated database management software. The line-by-line portion of the database contains spectroscopic parameters for 38 molecules and their isotopologues and isotopomers suitable for calculating atmospheric transmission and radiance properties. Many more molecular species are presented in the infrared cross-section data than in the previous edition, especially the chlorofluorocarbons and their replacement gases. There is now sufficient representation so that quasi-quantitative simulations can be obtained with the standard radiance codes. In addition to the description and justification of new or modified data that have been incorporated since the last edition of HITRAN (1996), future modifications are indicated for cases considered to have a significant impact on remote-sensing experiments.

Theoretical Study of Two-Photon Absorption Properties of a Series of Double-Layer Paracyclophane Derivatives

The equilibrium geometries, electronic structures, and one- and two-photon absorption properties of a series of paracyclophane derivatives have been determined by using the AM1 and ZINDO methods. The results show that the paracyclophane core as a multidimensional tunneling barrier remarkably increases the two-photon absorption cross section of molecules. As far as this series of paracyclophane derivatives is concerned, there exists a nonconventional “through-space” charge transfer. Our theoretical findings are consistent with recent experimental observations. It is found that the molecular length plays the most crucial role in the one-photon absorption intensity and the two-photon absorption cross section. For molecules with a given framework, a symmetrical structure with strong donor groups can result in a maximum two-photon absorption cross section. The three-state approximation is applicable to this series of paracyclophane derivatives. It is notable that paracyclophane-based molecules may afford advantages in the tradeoff of nonlinearity and transparency by generating a strong NLO response while providing a favorable displacement of the region of transparency.

Analysis of Ablation Characteristics of Absorbing Dielectrics Caused by Short Laser Pulses

The effect of ablation of absorbing dielectrics by single and two successive ultra short pulses from an excimer laser source is investigated. The numerical model is based on two photon absorption by the molecular chromophores followed by thermal degradation and diffusion, whereas ablation occurs through sublimation of the material from the surface. The numerical analysis involves solving a set of coupled three- or two-level chromophore rate equations, heat diffusion equation, and the transient radiative transport equation, using two techniques: a fully implicit iterative scheme and a predictor corrector technique (Fromm's scheme). Results for the temperature distribution and ablation depth are obtained for different laser parameters such as the delay time between two successive pulses, laser pulse width, laser fluence, and various material properties such as activation energy, relaxation time, thermal conductivity, and absorption cross section of molecules. The results obtained by consideration of the transient radiative transfer equation are compared with the steady-state formulation, and significant differences are observed in the temperature profiles and the ablation depth.