Absorption Quantum Research Articles

High intersubband absorption in long-wave quantum well infrared photodetector based on waveguide resonance

A hybrid structure consisting of periodic gold stripes and an overlaying gold film has been proposed as the optical coupler of a long-wave quantum well infrared photodetector. Absorption spectra and field distributions of the structure at back-side normal incidence are calculated by the finite difference time-domain method. The results indicate that the intersubband absorption can be greatly enhanced based on the waveguide resonance as well as the surface plasmon polariton (SPP) mode. With the optimized structural parameters of the periodic gold stripes, the maximal intersubband absorption can exceed 80%, which is much higher than the SPP-enhanced intersubband absorption (<50%) and about 6 times the one of the standard device. The relationship between the structural parameters and the waveguide resonant wavelength is derived. Other advantages of the efficient optical coupling based on waveguide resonance are also discussed.

Tunability of the optical absorption and refractive index changes in step-like and parabolic quantum wells under external electric field

In this paper, the effects of an external electric field on the energy transitions and optical absorption lineshape in step and parabolic GaAs quantum wells are theoretically investigated. The energy separations between the three lowest energy levels E1, E2 and E3 and their corresponding wavefunctions are calculated by solving the Schrödinger equation. Our theoretical findings show that the intersubband transitions and the optical absorption in the step-like quantum well can be tuned and controlled by an applied electric field (F). Especially the optical absorption coefficient α12(ω) presents a blue shift by increasing the intensity of F. Contrary to the case of step-like quantum well, the energy transition and the optical absorption coefficient α12(ω) are less sensitive to the applied electric field F in the case of parabolic quantum well. In the latter case α12(ω) presents a small red-shift variation. The obtained behavior in the optical absorption coefficient and refractive index changes can be used to design and fabricate new optical devices such as optical modulators.

Measurements of the intrinsic quantum efficiency and absorption length of tetraphenyl butadiene thin films in the vacuum ultraviolet regime

A key enabling technology for many liquid noble gas (LNG) detectors is the use of the common wavelength shifting medium tetraphenyl butadiene (TPB). TPB thin films are used to shift ultraviolet scintillation light into the visible spectrum for detection and event reconstruction. Understanding the wavelength shifting efficiency and optical properties of these films are critical aspects in detector performance and modeling and hence in the ultimate physics sensitivity of such experiments. This article presents the first measurements of the room-temperature microphysical quantum efficiency for vacuum-deposited TPB thin films – a result that is independent of the optics of the TPB or substrate. Also presented are measurements of the absorption length in the vacuum ultraviolet regime, the secondary re-emission efficiency, and more precise results for the “black-box” efficiency across a broader spectrum of wavelengths than previous results. The low-wavelength sensitivity, in particular, would allow construction of LNG scintillator detectors with lighter elements (Ne, He) to target light mass WIMPs.

Simultaneous measurement of quantum yield ratio and absorption ratio between acceptor and donor by linearly unmixing excitation-emission spectra.

Quantum yield ratio (QA /QD ) and absorption ratio (KA /KD ) in all excitation wavelengths used between acceptor and donor are indispensable to quantitative fluorescence resonance energy transfer (FRET) measurement based on linearly unmixing excitation-emission spectra (ExEm-spFRET). We here describe an approach to simultaneously measure QA /QD and KA /KD values by linearly unmixing the excitation-emission spectra of at least two different donor-acceptor tandem constructs with unknown FRET efficiency. To measure the QA /QD and KA /KD values of Venus (V) to Cerulean (C), we used a wide-field fluorescence microscope to image living HepG2 cells separately expressing each of four different C-V tandem constructs at different emission wavelengths with 435 nm and 470 nm excitation respectively to obtain the corresponding excitation-emission spectrum (SDA ). Every SDA was linearly unmixed into the contributions (weights) of three excitation-emission spectra of donor (WD ) and acceptor (WA ) as well as donor-acceptor sensitisation (WS ). Plot of WS /WD versus WA /WD for the four C-V plasmids from at least 40 cells indicated a linear relationship with 1.865 of absolute intercept (QA /QD ) and 0.273 of the reciprocal of slope (KA /KD ), which was validated by quantitative FRET measurements adopting 1.865 of QA /QD and 0.273 of KA /KD for C32V, C5V, CVC and VCV constructs respectively in living HepG2 cells.

Binding energy of donor impurity states and optical absorption in the Tietz-Hua quantum well under an applied electric field

For a quantum well which has the Tietz-Hua potential, the ground and some excited donor impurity binding energies and the total absorption coefficients, including linear and third order nonlinear terms for the transitions between the related impurity states with respect to the structure parameters and the impurity position as well as the electric field strength are investigated. The binding energies were obtained using the effective-mass approximation within a variational scheme and the optical transitions between any two impurity states were calculated by using the density matrix formalism and the perturbation expansion method. Our results show that the effects of the electric field and the structure parameters on the optical transitions are more pronounced. So we can adjust the red or blue shift in the peak position of the absorption coefficient by changing the strength of the electric field as well as the structure parameters.

The case of escape probability as linear in short time

We derive rigorously the short-time escape probability of a quantum particle from its compactly supported initial state, which has a discontinuous derivative at the boundary of the support. We show that this probability is linear in time, which seems to be a new result. The novelty of our calculation is the inclusion of the boundary layer of the propagated wave function formed outside the initial support. This result has applications to the decay law of the particle, to the Zeno behaviour, quantum absorption, time of arrival, quantum measurements, and more.

Qubit absorption refrigerator at strong coupling

We demonstrate that a quantum absorption refrigerator (QAR) can be realized from the smallest quantum system, a qubit, by coupling it in a non-additive (strong) manner to three heat baths. This function is un-attainable for the qubit model under the weak system-bath coupling limit, when the dissipation is additive. In an optimal design, the reservoirs are engineered and characterized by a single frequency component. We then obtain closed expressions for the cooling window and refrigeration efficiency, as well as bounds for the maximal cooling efficiency and the efficiency at maximal power. Our results agree with macroscopic designs and with three-level models for QARs, which are based on the weak system-bath coupling assumption. Beyond the optimal limit, we show with analytical calculations and numerical simulations that the cooling efficiency varies in a non-universal manner with model parameters. Our work demonstrates that strongly-coupled quantum machines can exhibit function that is un-attainable under the weak system-bath coupling assumption.

Exciton states and direct interband light absorption in the ensemble of toroidal quantum dots

One electron and exciton states in toroidal quantum dot (QD) have been considered. The convenient coordinate system has been defined and the Schrodinger equation has been solved in these coordinates. The electron energy spectrum and wave function dependence on the geometrical parameters of toroidal QD have been obtained. The comparison with the results obtained by numerical methods has been done. Optical absorption has been considered in both cases of “small” toroid when the interaction of an electron and a hole is neglected and cases of relatively “large” toroid when the correlation between the particles has been taken into account. Interband optical transitions have been considered in the ensemble of toroidal QDs. The selection rules for quantum transitions and absorption edge dependence on the geometrical parameters have been obtained.

Ultra-thin infrared metamaterial detector for multicolor imaging applications.

The next generation of infrared imaging systems requires control of fundamental electromagnetic processes - absorption, polarization, spectral bandwidth - at the pixel level to acquire desirable information about the environment with low system latency. Metamaterial absorbers have sparked interest in the infrared imaging community for their ability to enhance absorption of incoming radiation with color, polarization and/or phase information. However, most metamaterial-based sensors fail to focus incoming radiation into the active region of a ultra-thin detecting element, thus achieving poor detection metrics. Here our multifunctional metamaterial absorber is directly integrated with a novel mid-wave infrared (MWIR) and long-wave infrared (LWIR) detector with an ultra-thin (~λ/15) InAs/GaSb Type-II superlattice (T2SL) interband cascade detector. The deep sub-wavelength metamaterial detector architecture proposed and demonstrated here, thus significantly improves the detection quantum efficiency (QE) and absorption of incoming radiation in a regime typically dominated by Fabry-Perot etalons. Our work evinces the ability of multifunctional metamaterials to realize efficient wavelength selective detection across the infrared spectrum for enhanced multispectral infrared imaging applications.

Improved Method of Fluorescence Quantum Yield Determination.

In the most widely used procedure for luminescence quantum yield determination, absorption and emission spectra are measured on two different instruments. This leads to errors caused by wavelength misalignment and different monochromator characteristics of the spectrophotometer and the spectrofluorometer. These errors can be avoided using a method for fluorescence quantum yield determination that relies on simultaneous absorption and fluorescence emission (SAFE) measurement using a single commercial spectrofluorometer. The method's performance is compared with the standard routinely used procedure for the relative quantum yield determination. The advantages of SAFE measurement are discussed. The proposed novel approach eliminates a number of potential errors in quantum yield determination protocol and provides higher accuracy.

Perovskite quantum dots integrated in large-area luminescent solar concentrators

Luminescent solar concentrators (LSCs) are considered a promising technology to reduce the cost of electricity by decreasing the use of expensive photovoltaic materials, such as single-crystal silicon. In addition, LSCs are suitable for applications in building-integrated photovoltaics. Inorganic perovskite quantum dots (QDs) are promising candidates as absorbers/emitters in LSCs, due to their excellent optical properties including size/chemical-composition dependent absorption/emission spectrum, high absorption coefficient, high quantum yield and good stability. However, due to the large overlap between their absorption and emission spectra, it is still very challenging to fabricate large-area high-efficiency LSCs using perovskite QDs. Here we report the synthesis of mixed-halide perovskite CsPb(BrxI1−x)3 QDs with small overlap of absorption and emission spectra, high quantum yield (over 60%) and absorption spectrum ranging from 300 to 650nm. We use these QDs to build semi-transparent large-area LSCs that exhibit an external optical efficiency of 2% with a geometrical gain factor of 45 (9cm in length). To date, these represent the brightest and most efficient solution-processed perovskite QDs based LSCs compared to LSCs based on perovskite thin films. The LSCs exhibit long term air stability without any noticeable variation in photoluminescence and lifetime under 4 W UV light illumination for over four hours.

Multiple-Color-Generating Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells via Dichroic Film Incorporation for Power-Generating Window Applications.

There are four prerequisites when applying all types of thin-film solar cells to power-generating window photovoltaics (PVs): high power-generation efficiency, longevity and high durability, semitransparency or partial-light transmittance, and colorful and aesthetic value. Solid-type thin-film Cu(In,Ga)S2 (CIGS) or Cu(In,Ga)(S,Se)2 (CIGSSe) PVs nearly meet the first two criteria, making them promising candidates for power-generating window applications if they can transmit light to some degree and generate color with good aesthetic value. In this study, the mechanical scribing process removes 10% of the window CIGSSe thin-film solar cell with vacant line patterns to provide a partial-light-transmitting CIGSSe PV module to meet the third requirement. The last concept of creating distinct colors could be met by the addition of reflectance colors of one-dimensional (1D) photonic crystal (PC) dichroic film on the black part of a partial-light-transmitting CIGSSe PV module. Beautiful violets and blues were created on the cover glass of a black CIGSSe PV module via the addition of 1D PC blue-mirror-yellow-pass dichroic film to improve the aesthetic value of the outside appearance. As a general result from the low external quantum efficiency (EQE) and absorption of CIGSSe PVs below a wavelength of 400 nm, the harvesting efficiency and short-circuit photocurrent of CIGSSe PVs were reduced by only ∼10% without reducing the open-circuit voltage (VOC) because of the reduced overlap between the absorption spectrum of CIGSSe PV and the reflectance spectrum of the 1D PC blue-mirror-yellow-pass dichroic film. The combined technology of partial-vacancy-scribed CIGSSe PV modules and blue 1D PC dichroic film can provide a simple strategy to be applied to violet/blue power-generating window applications, as such a strategy can improve the transparency and aesthetic value without significantly sacrificing the harvesting efficiency of the CIGSSe PV modules.

Behavioural and physiological limits to vision in mammals.

Human vision is exquisitely sensitive-a dark-adapted observer is capable of reliably detecting the absorption of a few quanta of light. Such sensitivity requires that the sensory receptors of the retina, rod photoreceptors, generate a reliable signal when single photons are absorbed. In addition, the retina must be able to extract this information and relay it to higher visual centres under conditions where very few rods signal single-photon responses while the majority generate only noise. Critical to signal transmission are mechanistic optimizations within rods and their dedicated retinal circuits that enhance the discriminability of single-photon responses by mitigating photoreceptor and synaptic noise. We describe behavioural experiments over the past century that have led to the appreciation of high sensitivity near absolute visual threshold. We further consider mechanisms within rod photoreceptors and dedicated rod circuits that act to extract single-photon responses from cellular noise. We highlight how these studies have shaped our understanding of brain function and point out several unresolved questions in the processing of light near the visual threshold.This article is part of the themed issue 'Vision in dim light'.

Spectral dependence of electrical energy-based photosynthetic efficiency at single leaf and canopy levels in green- and red-leaf lettuces

The spectrum of light affects both the electrical energy consumption by plants and photosynthetic efficiency. In a plant factory, where light-emitting diodes (LEDs) serve as an alternative to solar light, the optimal spectrum of light should be carefully chosen to maximize the rate of photosynthesis and the electrical energy efficiency of the crop. The objectives of this study were to investigate the photosynthetic rate of different colored lettuces (reddish and green leaves), to quantify the spectral dependence of photosynthetic efficiency, and to optimize the LED spectrum for maximum canopy photosynthesis and electrical energy consumption in lettuce grown in a plant factory. Two lettuce cultivars (Lactuca sativa L.), ‘JeokChukMyeon’ and ‘CheongChukMyeon’, were assessed for light absorption and photosynthetic efficiency at the single leaf and canopy levels, and the relative consumption of electrical energy from the LED lights was measured at 18 narrow wavelength bands of 10 nm from 400 to 700 nm. Anthocyanin and chlorophyll content (SPAD value) were measured and correlated with leaf color. Light interception by the canopy was estimated with light transmittance models. The light absorption was similar among the green and reddish lettuce cultivars at most wavelengths, but slightly higher in the reddish leaves around 550 nm (green region). In the reddish leaves, photosynthetic rates per incident photon of a single leaf had two peaks at 650-660 and 400-410 nm, while the photosynthetic rate per absorbed photon had three peaks at 650-660, 400-410, and 540-560 nm. In the green region of the light spectrum, both photosynthetic rates per incident photon and those per absorbed photon were lower in the reddish cultivars than in the green cultivars. The spectral dependence of light absorption at the canopy level was much weaker than that at the single leaf level. The quantum yield and absorption of green light at the canopy level were nearly same as those of blue and red lights, indicating that the photosynthetic efficiency of green light at the canopy level was higher than that at the single leaf level. The relative electrical energy consumption was lower in the green region than in the red and blue regions. Therefore, the photosynthetic efficiency based on electrical energy consumption at the canopy level was much lower with green LEDs than with blue or red LEDs. These results describe the plant response to the light spectrum at the canopy level and can be useful for optimizing artificial lighting sources for maximum plant productivity and energy-savings in a plant factory.

Tuning the terahertz absorption in cylindrical quantum wire

Terahertz absorption in cylindrical quantum well wire under the influence of unsymmetrical electric field is investigated. The two dimensional Schrödinger equation is solved using finite difference method to obtain the eigen states and energies. The absorption spectrum is calculated using the density matrix approach. Resultsreveal that the absorption peaks are in the terahertz range for specific values of physical parameters. Also the results show that the frequency and amplitude of the absorption peak are completely tunable by changing the electric field and the wire diameter.

Specific features of the electronic structure and spectral characteristics of the Gd5Si3 compound

The electronic structure and optical properties of the hexagonal intermetallic compound Gd5Si3 are investigated. The spin-polarization calculation of the band spectrum is performed in the local spin density approximation, taking account for the strong electron correlations in the 4 f shell of a Gd ion (LSDA + U method). Optical constants of the compound in the wavelength range of 0.22–15 μm are determined by the ellipsometry technique and some spectral characteristics are calculated. The frequency dependence of optical conductivity in the light quantum absorption region is analyzed on the basis of the calculated electron density of states.

Evaluation of the effects of low-intensity laser radiation in treatment of chronic salpingo-oophoritis in women

Background: The paper presents the data of an evaluation of low-intensity infrared laser radiation in the treatment of women with chronic salpingo-oophoritis (CSO). Aims and Objective: The research was aimed to determine effects of low-intensity laser radiation (LILR) in the treatment of CSO in women based on individual sensitivity, interleukin (IL) blood levels, and clinical success rates of the treatment. The research object included 74 women of reproductive age. Materials and Methods: The evaluation of the treatment was performed based on a study of blood serum individual sensitivity to a selected mode of laser radiation, blood cytokine levels (IL - 1β, 4, 6), and clinical success rates of the treatment. Results: The effects of LILR in women with CSO are aimed at inhibiting the production of inflammatory mediators following the activation of quantum absorption and generation of secondary radiations and a bio-energetic resonance. Conclusion: Women’s body being highly sensitive to infrared laser radiation substantially increases clinical success rates of the treatment compared to the treatment without laser therapy (pain relief, reducing a number of disease recurrences, reducing obstruction of the fallopian tubes).

Autonomous quantum refrigerator in a circuit QED architecture based on a Josephson junction

An implementation of a small quantum absorption refrigerator in a circuit QED architecture is proposed. The setup consists of three harmonic oscillators coupled to a Josephson unction. The refrigerator is autonomous in the sense that it does not require any external control for cooling, but only thermal contact between the oscillators and heat baths at different temperatures. In addition, the setup features a built-in switch, which allows the cooling to be turned on and off. If timing control is available, this enables the possibility for coherence-enhanced cooling. Finally, we show that significant cooling can be achieved with experimentally realistic parameters and that our setup should be within reach of current technology.

The role of the electronic structure and solvent in the dye-sensitized solar cells based on Zn-porphyrins: Theoretical study

In this work, using the density functional theory (DFT) and time-dependent DFT (TD-DFT), we have theoretically studied the electronic structures, quantum reactivity parameters and absorption spectra of the several dyes based on Zn-porphyrin derivatives in the gas phase, methanol (MeOH) and tert-buthanol (t-BuOH). Also, open-circuit photovoltage (VOC), exciton binding energy (EBE), light harvesting efficiency (LHE), the free energy change of regeneration (ΔGregen·(dye)), and the free energy change of electron injection (ΔGinject) have been investigated. The studied dyes in the presence of the solvents showed a smaller gap of the highest occupied molecular orbital (HOMO) – the lowest unoccupied molecular orbital (LUMO) and lower EBE, a higher intensity and oscillator strength and red shift in the absorption spectra. These changes facilitate the charge transfer (CT) phenomena in the nano-structures of the dyes and improve the solar cell efficiency. Chemical modifications of the dyes by electron donor groups or conjugated system extension, improve the incident photon to current conversion efficiency (IPCE), the energy gap between the LUMO of the dye and the conduction band (CB) of the TiO2 (eVOC), and the LHE of these dye-sensitized solar cells (DSSCs). Finally, some correlations between the molecular descriptors and solar cell parameters were analyzed.

Optical gain in GaAsBi/GaAs quantum well diode lasers.

Electrically pumped GaAsBi/GaAs quantum well lasers are a promising new class of near-infrared devices where, by use of the unusual band structure properties of GaAsBi alloys, it is possible to suppress the dominant energy-consuming Auger recombination and inter-valence band absorption loss mechanisms, which greatly impact upon the device performance. Suppression of these loss mechanisms promises to lead to highly efficient, uncooled operation of telecommunications lasers, making GaAsBi system a strong candidate for the development of next-generation semiconductor lasers. In this report we present the first experimentally measured optical gain, absorption and spontaneous emission spectra for GaAsBi-based quantum well laser structures. We determine internal optical losses of 10–15 cm−1 and a peak modal gain of 24 cm−1, corresponding to a material gain of approximately 1500 cm−1 at a current density of 2 kA cm−2. To complement the experimental studies, a theoretical analysis of the spontaneous emission and optical gain spectra is presented, using a model based upon a 12-band k.p Hamiltonian for GaAsBi alloys. The results of our theoretical calculations are in excellent quantitative agreement with the experimental data, and together provide a powerful predictive capability for use in the design and optimisation of high efficiency lasers in the infrared.