Single Photon Energy Research Articles

Intense visible emission from ZnO/PAAX (X = H or Na) nanocomposite synthesized via a simple and scalable sol-gel method.

Intense visible nano-emitters are key objects for many technologies such as single photon source, bio-labels or energy convertors. Chalcogenide nanocrystals have ruled this domain for several decades. However, there is a demand for cheaper and less toxic materials. In this scheme, ZnO nanoparticles have appeared as potential candidates. At the nanoscale, they exhibit crystalline defects which can generate intense visible emission. However, even though photoluminescence quantum yields as high as 60% have been reported, it still remains to get quantum yield of that order of magnitude which remains stable over a long period. In this purpose, we present hybrid ZnO/polyacrylic acid (PAAH) nanocomposites, obtained from the hydrolysis of diethylzinc in presence of PAAH, exhibiting quantum yield systematically larger than 20%. By optimizing the nature and properties of the polymeric acid, the quantum yield is increased up to 70% and remains stable over months. This enhancement is explained by a model based on the hybrid type II heterostructure formed by ZnO/PAAH. The addition of PAAX (X = H or Na) during the hydrolysis of ZnEt2 represents a cost effective method to synthesize scalable amounts of highly luminescent ZnO/PAAX nanocomposites.

All-solid-state deep ultraviolet laser for single-photon ionization mass spectrometry.

We report here the development of a reflectron time-of-flight mass spectrometer utilizing single-photon ionization based on an all-solid-state deep ultraviolet (DUV) laser system. The DUV laser was achieved from the second harmonic generation using a novel nonlinear optical crystal KBe2BO3F2 under the condition of high-purity N2 purging. The unique property of this laser system (177.3-nm wavelength, 15.5-ps pulse duration, and small pulse energy at ∼15 μJ) bears a transient low power density but a high single-photon energy up to 7 eV, allowing for ionization of chemicals, especially organic compounds free of fragmentation. Taking this advantage, we have designed both pulsed nanospray and thermal evaporation sources to form supersonic expansion molecular beams for DUV single-photon ionization mass spectrometry (DUV-SPI-MS). Several aromatic amine compounds have been tested revealing the fragmentation-free performance of the DUV-SPI-MS instrument, enabling applications to identify chemicals from an unknown mixture.

The influences of multiphoton excitation on near-threshold Harmonic emission in atoms

When an atom or a molecule interacts with an intense laser field, a coherent high-order harmonic emission is observed at a frequency that is an integer multiple magnitude of the initial frequency of the incident laser field. The harmonic emission has the characteristic of high emission efficiency at relatively high orders, and it also has a wide expansion in the frequency domain. Thus, the high-order harmonic generation can be utilized to generate coherent EUV or soft X-ray light sources as well as ultrashort at to second laser pulses. It is promising that the attosecond laser pulse will be an important tool for detecting and controlling the electron dynamics in atom and molecule systems. The mechanisms of high-order harmonics especially the high energy part of the harmonic spectrum can be explained by the well-known three-step model. The three-step model assumes that the electron in the bound state firstly are ionized by the potential barrier formed by the laser electric field and the atomic potential, then the ionized electrons oscillate in the laser field, and finally the electron with high kinetic energy gained in the laser field has the possibility to return back to the parent ion and recombines with the ground state of the system with a high energy photon emitted. As for harmonics with low orders, especially those with single photon energy near the ionization threshold, the Coulomb potential of the atom has significant influences on them. However,the effect of the Coulomb potential of the atom are not included in the three-step model, so the mechanism of near-threshold harmonics (NTH) cannot be clearly interpreted with the three-step model alone. In this circumstance, the study of the mechanism of near-threshold harmonic emission attracted people's attention in general. One important application of NTH is that it can be utilized to generate optical comb with EUV frequencies. Theoretically, Xiong et al. studied the mechanism of below-threshold harmonic (BTH) emission and found that the mechanism of this part of harmonics include the effect of the quantum-path interference and the Coulomb potential. He et al. analyzed the emission of BTH in various laser intensity regions and found that the harmonic spectrum exhibits a periodic structure as a function of the harmonic frequency when the incident laser intensity is about 1013 W/cm2. Utilizing the quantum-path and time-frequency analyses of the harmonic emission, He et al. indicated that this periodic structure can be attributed to the interference effect between two specific quantum paths. Li et al. adopted the synchrosqueezing scheme to study the near-and below-threshold harmonic emission of Cs atoms in an intense mid-infrared laser field and they showed that the multiphoton and the multiple rescattering trajectories have an effect on the NTH and BTH generation processes. Shafir et al. found that the ionic potential plays an critical role in NTH emission. Under the interaction between the atom and the intense laser field, electron in the ground state not only can be ionized but also be pumped into excited state, and these excitation processes also affect the harmonic emission. We studied the harmonic emission process near the ionization threshold by solving the time-dependent Schrdinger equation of an atom interacting with a strong laser field. Utilizing the obtained wavefunction, we systematically studied the high-order harmonic emission with the variation of the incident laser intensity. Meanwhile, through solving the TDSE with the momentum-space method, the excited-state population is precisely calculated and achieved. We show that the ninth harmonic exhibits a periodic oscillation structure with the intensity of the incident laser field increasing, and we reveals that there is a synchronous variation between the harmonic intensity and the relatively high bound state population.Within a certain range of laser intensity, the increase of the total population of the excited states corresponds to the low efficiency of harmonic emission, and this competition relationship is quite clear. Therefore, when the wavelength of the driving laser pulse is fixed, we can optimize the driving laser intensity to achieve the near-threshold harmonic emission with high efficiency.

Energy-tunable single-photon light-emitting diode by strain fields

We report a strain-tunable quantum light-emitting diode for generation of electrically triggered and energy-tunable single photons. The device consists of a p-i-n quantum dots containing nanomembrane integrated onto a piezoelectric actuator. By injecting ultrafast voltage pulses, electrically driven light emission is realized and the quantum nature of single-photon emission is revealed in the second-order time correlation measurements. In addition to electrically pulsed excitation, we achieved a broad tuning range ( $${\sim }$$ 9 meV) to the energy of the emitted single photons by imposing giant biaxial strain fields on quantum dots within the diode. We further show that energy of the single-photon emission emitted from different quantum dots can be tuned to degeneracy, thus rendering the quantum interference on which most of existing photonic quantum technologies rely. The device reported in this work represents an important step toward the realization of quantum repeater by using electrically triggered quantum light sources of indistinguishable photons.

28.3 W 355 nm laser generated by efficient third-harmonic in CsB3O5 crystal

Ultraviolet laser operating at 355 nm has been found to have wide applications in scientific and industrial fields of laser radar, biological fluorescence medicine, micro processing, laser marking and laser ablation, owing to its superior properties of short wavelength, high single-photon energy, and high resolution. In addition, 355 nm laser plays a vital role in promoting the development of RGB full color display because it can be used as an excitation source for investigating the blue light emitting materials. LiB3O5 (LBO) crystal possesses relatively high nonlinear coefficient and high optical damage threshold. Therefore, it is generally employed to generate 355 nm light through the third harmonic generation (THG) of the Nd:YAG laser (1064 nm). However, the CsB3O5(CBO) crystal, which also belongs to B3O7 group has attracted more attention for its larger nonlinear coefficient. The temperature sensitivity is another important characteristic of the nonlinear crystal. Temperature fluctuation can cause the variation of refractive index of nonlinear optical crystal, which leads to phase mismatch and thus affects the nonlinear conversion efficiency. The principal refractive index of CBO crystal was accurately measured using the auto-collimation method in a temperature range from 40 to 190 ℃ for the first time by Zhang et al. in 2013 [Zhang G C, et al. 2013 Opt. Lett. 38 1594], while the temperature bandwidth of CBO for 355 nm THG has not been reported. In the present paper, a high-power 355 nm laser is produced by efficient THG of an acousto-optic Q-switched quasicontinuous wave 1064 nm laser in CBO crystal. The master-oscillation power-amplification (MOPA) system with Nd:YAG crystal which is side pumped by high-power pulsed laser diode (LD) array delivers 210 W of a quasi-continuous Q-switched 1064 nm laser power. The laser operates at a 1 kHz repetition rate, and each pulse train contains five Q-switched pulses each with a duration of 40 ns. The 98 W of 532 nm green light is produced by second-harmonic generated in type-I LBO crystal. The 28.3 W ultraviolet laser is achieved by a 30-mm type-II CBO crystal through the sum frequency of 1064 nm and 532 nm light. The conversion efficiency from the fundamental light to the third harmonic reaches 13.5%, which is 28.6% higher than that obtained with a type-II LBO crystal under the same experimental conditions. The temperature sensitivity of CBO crystal in the 355 nm THG process is studied. Its temperature bandwidth is 25, which is much broader than that of LBO crystal. The experimental results show that the CBO crystal is superior to LBO crystal in the sense of conversion efficiency and temperature sensitivity for THG of 355 nm.

In English

Experimental and theoretical aspects of fullerene C60 ionization, fragmentation and aggregation are discussed by laser desorption/ionization mass spectrometry and quantum chemistry. Ion formation and chemical reactions of fullerene molecule depend essentially upon the nature and properties of the surface where it is deposited as well as upon the conditions of deposition and the mechanisms of ion-molecular reactions which occur in the ion source of mass spectrometer.It has been shown that the energy of single photon is enough to ionize an adsorbed fullerene molecule due to transition of single electron to the Fermi level of support and consequent overcoming the barrier of image forces. Nevertheless, this mechanism cannot explain the observed mass spectra completely, in particular the high level of fullerene fragmentation, because of lack of photon energy. Plasmon resonance resulted from multi-photon excitation of fullerene molecule in condensed state is the initial stage and the main mechanism of energy supply for fullerene laser induced ionization, fragmentation, aggregation, and chemical reactions which take place in both adsorbed state and ion plum. Explanation of observed experimental results concerning fullerene fragmentation and aggregation is proposed based on the results of quantum chemical calculations and on heuristic considerations.

Electronic structure of reconstructed InAs(001) surfaces — identification of bulk and surface bands based on their symmetries

Using angle-resolved photoelectron spectroscopy (ARPES) band structures of indium- and arsenic-terminated InAs(001) surfaces are investigated. These surfaces are highly reconstructed, elementary cells of their lattices contain many atoms in different chemical configurations, and moreover, they are composed of domains having related but different reconstructions. These domain-type surface reconstructions result in the reciprocal spaces containing regions with well-defined k→∥-vector and regions with not-well-defined one. In the ARPES spectra most of the surface related features appear as straight lines in the indeterminate k→∥-vector space. It is shown that, thanks to differences in crystal and surface symmetries, the single photon energy ARPES may be successfully used for classification of surface and bulk bands of electronic states on complex, highly reconstructed surfaces instead of the most often used variable photon energy studies.

Algebraic structure of the two-qubit quantum Rabi model and its solvability using Bogoliubov operators

We have found the algebraic structure of the two-qubit quantum Rabi model behind the possibility of its novel exceptional eigenstates with finite photon numbers by analyzing the Hamiltonian in the photon number space. The exceptional solutions with at most 1 photon exist in the whole qubit–photon coupling regime with constant eigenenergy equal to single photon energy , which can be clearly demonstrated from the Hamiltonian structure. With a similar method, we find that these special dark-state-like eigenstates (the eigenenergy is coupling-independent, but the wave function is coupling-dependent) commonly exist for the two-qubit Jaynes–Cummings model, with (), and one of them is also the eigenstate of the two-qubit quantum Rabi model, which is interesting for application in a simpler way. Besides, using Bogoliubov operators, we analytically retrieve the solution of the general two-qubit quantum Rabi model. In this concise and physical way, we clearly see how the eigenvalues of the infinite-dimensional two-qubit quantum Rabi Hamiltonian are determined by a convergent power series, so that the solution can reach arbitrary accuracy conveniently because of the convergence property.

Monte carlo simulation of in situ gamma-spectra recorded by NaI (Tl) detector in the marine environment

To develop a NaI (Tl) detector for in situ radioactivity monitoring in the marine environment and enhance the confidence of the probability of the gamma-spectrum analysis, Monte Carlo simulations using the Monte Carlo N-Particle ( MNCP ) code were performed to provide the response spectra of some interested radionuclides and the background spectra originating from the natural radionuclides in seawater recorded by a NaI (Tl) detector. A newly developed 75 mm × 75 mm NaI (Tl) detector was calibrated using four reference radioactive sources 137Cs, 60Co, 40K and 54Mn in the laboratory before the field measurements in seawater. A simulation model was established for the detector immersed in seawater. The simulated spectra were all broadened with Gaussian pulses to reflect the statistical fluctuations and electrical noise in the real measurement. The simulated spectra show that the single-energy photons into the detector are mostly scattering low-energy photons and the high background in the low energy region mainly originates from the Compton effect of the high energy ?-rays of natural radionuclides in seawater. The simulated background spectrum was compared with the experimental one recorded in field measurement and they seem to be in good agreement. The simulation method and spectra can be used for the accurate analysis of the filed measurement results of low concentration radioactivity in seawater.

Cavity optomechanics mediated by a quantum two-level system.

Coupling electromagnetic waves in a cavity and mechanical vibrations via the radiation pressure of photons is a promising platform for investigations of quantum–mechanical properties of motion. A drawback is that the effect of one photon tends to be tiny, and hence one of the pressing challenges is to substantially increase the interaction strength. A novel scenario is to introduce into the setup a quantum two-level system (qubit), which, besides strengthening the coupling, allows for rich physics via strongly enhanced nonlinearities. Here we present a design of cavity optomechanics in the microwave frequency regime involving a Josephson junction qubit. We demonstrate boosting of the radiation–pressure interaction by six orders of magnitude, allowing to approach the strong coupling regime. We observe nonlinear phenomena at single-photon energies, such as an enhanced damping attributed to the qubit. This work opens up nonlinear cavity optomechanics as a plausible tool for the study of quantum properties of motion.

Design of reflective quarter-wave plates in extreme ultraviolet

Using an optimization method of layer thicknesses based on a genetic algorithm, aperiodic multilayer structures are designed, which display excellent quarter-wave plate (QWP) characteristics for extreme ultraviolet (EUV) radiation in reflection. In addition, a broadband QWP with 3eV bandwidth in the EUV region, was also designed with the same optimization algorithm and an adapted merit function. The structural and reflective characteristics of single photon energy and broadband reflective QWPs have been explored numerically. Fabricating such optical components could allow polarization control of EUV radiations and ultrafast EUV pulses.

Development and Application of Portable Reference Radiation Fields with Multi-Point Single-Energy Photon

Based on the needs of detection and calibration with low-energy X-ray, we used the relationship characteristics of X-ray fluorescence, absorption and limit potential target excitation, developed the X-ray device with adjustable intensity (single photon to 107/s), optional energy points (4 keV - 20 keV), highly portable (≤1 kg), by the matching design of fluorescence energy conversion target and modulation means, coupled transport simulation of electron-photon in target, meanwhile, we solved the low-energy X-ray radiation field diagnose problems with HPGe detector, which calibrated with combined technique, including relatively wide energy efficiency simulation and single energy point of absolute efficiency calibration. In single-photon calibration field of soft X-ray pulsar navigation detect, the portable reference single energy radiation fields was applied effectively and got good result, the reference radiation fields provided perfect experiment means for the scientific study of pulsar navigation detecting, sun X-ray monitoring, etc.

Theoretical prediction of physical parameters of GexSb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys

Abstract Physical properties of GexSb20−x Te80 (x = 11, 13, 15, 17, 19) bulk glassy alloys are examined theoretically. Lone pair electrons are calculated using an average coordination number (〈r〉) and the number of valence electrons, and are found to decrease with an addition of Ge. Mean bond energy (〈E〉) is proportional to glass transition temperature (Tg) and shows maxima near the chemical threshold. Cohesive energy of the system is calculated using chemical bond approach. A linear relation is found between cohesive energy, band gap (calculated theoretically and confirmed experimentally) and average heat of atomization. All these parameters are increasing with an increase in Ge content. A relation between average single bond energy and photon energy is discussed. Compactness of the structure is measured from the calculated density of the glass. An attempt is made to discuss the results in terms of structure of the glass or equivalently with average coordination number.

A compact and portable X-ray beam position monitor using Medipix3

The present work reports on the design and implementation of a novel portable X-ray beam diagnostics (XBPM) device. The device is transparent to the X-ray beam and provides real-time measurements of beam position, intensity, and size. The measurement principle is based on a pinhole camera which records scattered radiation from a Kapton foil which is placed in the beam path. The use of hybrid detectors (Medipix3) that feature a virtually noiseless readout system with capability of single photon detection and energy resolving power enables the diagnostics with a better resolution and higher sensitivity compared to the use of traditional indirect X-ray detection schemes. We describe the detailed system design, which consists of a vacuum compatible focal plane sensor array, a sensor conditioning and readout board and a heterogeneous data processing unit, which also acts as a network server that handles network communications with clients. The readout protocol for the Medipix3 sensor is implemented using field programmable gate array (FPGA) logic resulting in a versatile and scalable system that is capable of performing advanced functions such as data compression techniques and feature extraction. For the system performance measurements, we equipped the instrument with a single Medipix3 die, bump bonded to a Si sensor, rather than four for which it was designed. Without data compression, it is capable of acquiring magnified images and profiles of synchrotron X-ray beams at a transfer rate through Ethernet of 27 frames/s for one Medipix3 die.

Analysis of radiation pressure induced nonlinear optofluidics

We analyze two nonlinear optofluidic processes where nonlinearity is induced by the interplay between optical field and liquid interface. Specifically, guided optical waves generate radiation pressure on the liquid interface, which can in turn distort the liquid interface and modify the properties of the optical field. In the first example, we discuss the feasibility of nonlinear optofluidic solitons, where optical field is governed by the nonlinear Schrödinger equation and nonlinearity is effectively determined by liquid properties. Then, we analyze a nonlinear optofluidic process associated with a high quality (Q) factor whispering gallery mode (WGM) in a liquid droplet. Similar to Kerr effects, the WGM can produce a frequency shift proportional to the WGM power. Using liquid properties that are experimentally attainable, we find that it may only take a few photons to generate measurable WGM resonance shift. Such a possibility may eventually lead to nonlinear optics at single photon energy level.

Study on UV Laser Cutting Carbon Fibre Reinforced Composites

Obtaining narrower kerf and smaller heat affected zone (HAZ) is a difficulty in laser cutting carbon fiber reinforced plastic (CFRP) composites. In order to solve this problem, the experiments used a semiconductor UV laser to cut CFRP have been done and how laser parameters (include pulse power, repetition frequency, cutting speed and direction) influent the width and HAZ of kerf have been achieved. In the meantime, compared with infrared laser cutting CFRP, the quality of CFRP cut by different wavelength laser has been investigated. The results show that owing to CFRP has the characteristic of anisotropy, laser cutting direction is the most significant factor that affects the quality of kerf cut by UV laser. The study also found that owing to high single photon energy, the narrower kerf and smaller HAZ around kerf can be get by UV laser cutting CFRP, nevertheless, it can’t be achieved by infrared laser cutting CFRP.

SU-E-T-221: Investigation of Lower Energy (< 6 MV) Photon Beams for Cancer Radiotherapy

Purpose: To study the potential applications of the lower energy (< 6MV) photon beams in the radiotherapeutic management of pediatric cancer and lung cancer patients. Methods: Photon beams of 2, 3, 4, 5 and 6MV were first simulated with EGS4/BEAM and then used for Monte-Carlo dose calculations. For four pediatric patients with abdominal and brain lesions, six 3D-conformal radiotherapy (3DCRT) plans were generated using single photon energy (2 to 6MV) or mixed energies (3 and 6MV). Furthermore, a virtual machine of 3 and 6MV was commissioned in a treatment planning system (TPS) based on Monte-Carlo simulated data. Three IMRT plans of a lung cancer patient were generated on this virtual machine. All plans were normalized to D95% of target dose for 6MV plan and then compared in terms of integral dose and OAR sparing. Results: For the four pediatric patients, the integral dose for the 2, 3, 4 and 5MV plans increased by 9%, 5%, 3.5%, 1.7%, respectively as compared to 6MV. Almost all OARs in the 2MV plan received more than 10% more doses than 6MV. Mixed energy 3DCRT plans were of the same quality as 6MV plans. For the lung IMRT plans, both the 3MV plan and the mixed beam plan showed better OAR sparing in comparison to 6MV plan. Specifically, the maximum and mean doses to the spinal cord in the mixed energy plan were lower by 21% and 16%, respectively. Conclusion: Single lower energy photon beam was found to be inferior to 6MV in the radiotherapy of pediatric patients and lung cancer patients when the integral doses and the doses to the OARs were considered. However, mixed energy plans combining low with high energy beams showed significant OAR sparing while maintaining the same PTV coverage. Investigation with more patient data is ongoing for further confirmation.

TU-F-18A-09: CT Number Stability Across Patient Sizes Using Virtual-Monoenergetic Dual-Energy CT

Purpose: Virtual-monoenergetic imaging uses dual-energy CT data to synthesize images corresponding to a single photon energy, thereby reducing beam-hardening artifacts. This work evaluated the ability of a commercial virtual-monoenergetic algorithm to achieve stable CT numbers across patient sizes. Methods: Test objects containing a range of iodine and calcium hydroxyapatite concentrations were placed inside 8 torso-shaped water phantoms, ranging in lateral width from 15 to 50 cm, and scanned on a dual-source CT system (Siemens Somatom Force). Single-energy scans were acquired from 70-150 kV in 10 kV increments; dual-energy scans were acquired using 4 energy pairs (low energy: 70, 80, 90, and 100 kV; high energy: 150 kV + 0.6 mm Sn). CTDIvol was matched for all single- and dual-energy scans for a given phantom size. All scans used 128×0.6 mm collimation and were reconstructed with 1-mm thickness at 0.8-mm increment and a medium smooth body kernel. Monoenergetic images were generated using commercial software (syngo Via Dual Energy, VA30). Iodine contrast was calculated as the difference in mean iodine and water CT numbers from respective regions-of-interest in 10 consecutive images. Results: CT numbers remained stable as phantom width varied from 15 to 50 cm for all dual-energy data sets (except for at 50 cm using 70/150Sn due to photon starvation effects). Relative to the 15 cm phantom, iodine contrast was within 5.2% of the 70 keV value for phantom sizes up to 45 cm. At 90/150Sn, photon starvation did not occur at 50 cm, and iodine contrast in the 50-cm phantom was within 1.4% of the 15-cm phantom. Conclusion: Monoenergetic imaging, as implemented in the evaluated commercial system, eliminated the variation in CT numbers due to patient size, and may provide more accurate data for quantitative tasks, including radiation therapy treatment planning. Siemens Healthcare

Single photon energy dispersive x-ray diffraction

With the pressure range accessible to laser driven compression experiments on solid material rising rapidly, new challenges in the diagnosis of samples in harsh laser environments are emerging. When driving to TPa pressures (conditions highly relevant to planetary interiors), traditional x-ray diffraction techniques are plagued by increased sources of background and noise, as well as a potential reduction in signal. In this paper we present a new diffraction diagnostic designed to record x-ray diffraction in low signal-to-noise environments. By utilising single photon counting techniques we demonstrate the ability to record diffraction patterns on nanosecond timescales, and subsequently separate, photon-by-photon, signal from background. In doing this, we mitigate many of the issues surrounding the use of high intensity lasers to drive samples to extremes of pressure, allowing for structural information to be obtained in a regime which is currently largely unexplored.

Computational Modeling of the Dielectric Function of Silicon Slabs with Varying Thickness

The dynamical dielectric function of a silicon slab, in the region from near IR to UV light frequencies, is expected to vary with its thickness, and it is important to know whether its optical properties are similar to those of bulk silicon. Slabs of varying thickness are modeled starting from their atomic structure. Modeled Si(111) surfaces are terminated by hydrogen atoms to compensate the dangling bonds, and optical properties have been obtained for Si slabs with 4, 8, and 12 layers. Real and imaginary parts of the dielectric function are obtained from the polarization of the slab, expressed in terms of a delayed response function constructed from a reduced density matrix (RDM) which includes electronic dissipative effects due to coupling of photoexcited electrons to the substrate lattice and to electronic excitations. The related index of refraction and absorption coefficient have also been calculated from the above treatment. These optical properties are obtained using density functional theory (DFT) and plane wave basis sets to construct the equation of motion of a RDM, solved for steady light absorption. Both GGA (PBE) and hybrid (HSE) DFT exchange-correlation density functionals are employed to calculate the optical properties from the RDM. The imaginary part of the dielectric function is related to the light absorbance, and has been compared to measurements showing that better agreement is obtained with the HSE hybrid functional containing part of the exact short-range electronic exchange energy. We present a procedure by which one can reproduce the HSE results for the dielectric function from the computationally less expensive GGA PBE functional calculations, using a single photon energy shift parameter and results from PBE calculations. Our treatment shows that the onset of light absorption and strong diffraction are similar for thin slabs and bulk silicon, and that they have similar peak structure as functions of photon energy. Both properties increase with slab thickness at most photon energies. This makes silicon slabs reliable structures for photovoltaic applications.