Uniform Photon Research Articles

Comparative analysis of quantum two-way time transfer and quantum round-trip time transfer in consistent spatiotemporal settings

In this study, we conducted experiments using a single energy-time entangled biphoton source to compare the performance of quantum two-way time transfer (Q-TWTT) and quantum round-trip time transfer (Q-RTTT) under consistent spatiotemporal conditions. By conducting experiments with different fiber links of 11.3 km, 22.4 km, and 55.6 km, while ensuring uniform photon counts received by the single-photon detectors, we measured standard deviations (SDs) and stabilities of the time offsets. The measured SDs for Q-TWTT and Q-RTTT were 0.46 ps and 0.65 ps over the 11.3 km fiber, 1.14 ps and 1.3 ps over the 22.4 km fiber, 3.98 ps and 4.39 ps over the 55.6 km fiber, respectively. These results show good agreement with theoretical predictions, and the smaller SDs for Q-TWTT can be directly attributed to protocol-specific factors related to system symmetry. The long-term time stabilities of Q-TWTT and Q-RTTT were evaluated in terms of time deviation (TDEV). At an average time of 12680 s, the measured TDEVs were 0.49 ps and 0.63 ps for the 11.3 km fiber, 0.59 ps and 0.7 ps for the 22.4 km fiber, 1.01 ps and 1.36 ps for the 55.6 km fiber, respectively. The results validate that Q-TWTT exhibits superior time transfer performance compared to Q-RTTT, highlighting the advantages of Q-TWTT in practical applications.

DNA Framework-Guided Self-Limiting Aggregation for Highly Luminescent Metal Cluster Nanoaggregates.

The photoluminescent properties of atomically precise metal nanoclusters (MCs) have garnered significant attention in the fields of chemical sensing and biological imaging. However, the limited brightness of single-component nanoclusters hinders their practical applications, and the conventional ligand engineering approaches have proven insufficient in enhancing the emission efficiency of MCs. Here, we present a DNA framework-guided strategy to prepare highly luminescent metal cluster nanoaggregates. Our approach involves an amphiphilic DNA framework comprising a hydrophobic alkyl core and a rigid DNA framework shell, serving as a nucleation site and providing well-defined nanoconfinements for the self-limiting aggregation of MCs. Through this method, we successfully produced homogeneous MC nanoaggregates (10.1 ± 1.2 nm) with remarkable nanoscale precision. Notably, this strategy proves adaptable to various MCs, leading to a substantial enhancement in emission and quantum yield, up to 3011- and 87-fold, respectively. Furthermore, our investigation using total internal reflection fluorescence microscopy at the single-particle level uncovered a more uniform photon number distribution and higher photostability for MC nanoaggregates compared to template-free counterparts. This DNA-templating strategy introduces a conceptually innovative approach for studying the photoluminescent properties of aggregates with nanoscale precision and holds promise for constructing highly luminescent MC nanoparticles for diverse applications.

Efficient continuous synthesis of 2-hydroxycarbazole and 4-hydroxycarbazole in a millimeter scale photoreactor

2-Hydroxycarbazole and 4-hydroxycarbazole are important chemicals with extensive applications in optoelectronic materials and pharmaceutical field. State of the art yield of 2-hydroxycarbazole is ∼30% and the reaction time is typically in hours or days. Herein, we developed a green route for the continuous and high-throughput synthesis of 2-hydroxycarbazole and 4-hydroxycarbazole via photochemical intramolecular cyclization of 3‑hydroxy-2′‑chloro-diphenylamine using a self-designed millimeter scale photoreactor, which was designed based on sizing-up and numbering-up strategies for a decent liquid holdup (6.8 mL) and fabricated via femtosecond laser engraving technique. The photochemical synthesis was carried out continuously under the illumination of 365 nm UV-LED with dimethyl sulfoxide as solvent and potassium t-butoxide as catalyst. It was found that under optimized conditions a 2-hydroxycarbazole yield of 31.6% and a 4-hydroxycarbazole yield of 11.1% were obtained with a residence time of 1 min. Compared to semi-batch operations, the reaction time was shortened by 1–2 orders of magnitude. As a result, a throughput of 11.3 g/day 2-hydroxycarbazole and 4.0 g/day 4-hydroxycarbazole can be achieved from the photoreactor. It was proposed that the short reaction time and high product yield are resulted from higher photon transfer rates and more uniform photon distribution provided by the millimeter scale photoreactor, which enhances the reaction rates and mitigates overreaction.

Characterizing the Spatial Uniformity of Light Intensity and Spectrum for Indoor Crop Production

Maintaining uniform photon irradiance distribution above the plant canopy is a fundamental goal in controlled environment agriculture (CEA). Spatial variation in photon irradiance below the light saturation point will drive differences in individual plant development, decreasing the economic value of the crop. Plant growth is also affected by the spectral composition of light. So far, little attention has been paid to the quantification of the spatial variability in horticultural lighting applications. This work provides a methodology to benchmark and compare lighting installations used in indoor cultivation facilities. We measured the photon irradiance distributions underneath two typical grow light installations using a 10 × 10 measurement grid with 100 mm spacing. We calculated photon irradiance values for each grid point for 100 nm-wide blue, green, red and far-red wavebands covering the 400–800 nm range. We showed that the generally used uniformity metric defined as the minimum to average ratio of PPFD is not appropriate for the characterization of light uniformity in horticultural lighting applications. Instead, we propose to normalize photon irradiance to the maximum, analyze the histograms constructed from relative photon irradiance values and consider the light response of the cultivated crop while comparing the performance of CEA grow systems.

Fault-Tolerant Quantum Computation with Static Linear Optics

The scalability of photonic implementations of fault-tolerant quantum computing based on Gottesman-Kitaev-Preskill (GKP) qubits is injured by the requirements of inline squeezing and reconfigurability of the linear optical network. In this work we propose a topologically error-corrected architecture that does away with these elements at no cost—in fact, at an advantage—to state preparation overheads. Our computer consists of three modules: a two-dimensional (2D) array of probabilistic sources of GKP states; a depth-four circuit of static beam splitters, phase shifters, and short delay lines; and a 2D array of homodyne detectors. The symmetry of our proposed circuit allows us to combine the effects of finite squeezing and uniform photon loss within the noise model, resulting in more comprehensive threshold estimates. These jumps over both architectural and analytical hurdles considerably expedite the construction of a photonic quantum computer.Received 9 April 2021Accepted 15 November 2021DOI:https://doi.org/10.1103/PRXQuantum.2.040353Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMeasurement-based quantum computingOptical quantum information processingQuantum computationQuantum information architectures & platformsQuantum information processing with continuous variablesTopological quantum computingQuantum Information

Upconversion photoluminescence in colloidal CdSe/CdS nanocrystal-based solid films

Upconversion is the process based on the transformation of incoming low energy photons to higher energy emitted radiation. Upconverting materials are exploited in several novel applications like biolabeling and radiation harvesting, among others. Thanks to their intrinsic potential, it is very important to be able to fabricate functional devices based on such materials, and to do so in a controllable and affordable way. We investigated the below-bandgap stimulated radiation of heterostructures, obtained from core–shell semiconductor quantum dots, for the development of a large area upconverting system. The upconversion photoluminescence, after sintering of the nanoparticles, has been measured and the conversion mechanism investigated. The presence of intermediate states within the bandgap of the structure, derived from the specific quasi type-II configuration of the core–shell quantum dots, activated a uniform single photon upconversion mechanism on a wide surface area of the developed films, resulting in an anti-Stokes shift larger than 0.4 eV.

PHOTON FIELD OF ~100–200 KEV FOR ENVIRONMENTAL DOSEMETER CALIBRATION

As a reference photon field, several radionuclides have been used frequently, such as 241Am,137Cs and60 Co for calibration. These nuclides provide mono-energy photons for dosemeters covering few tens of keV-MeV. The main energy around 200keV is important for both environmental and medical fields since the former should consider scattering photons and the later should measure photons from X-ray generator. In our previous work, a backscattered layout can provide a uniform photon field spectra and dose rate with an energy of 190keV by using an affordable intensity 137 Cs gamma source. Several other quasi-monoenergetic photon fields in the range of 100-200keV could be obtained by using several available gamma sources. Two calibrated environmental CsI(Tl) survey meters, Horiba PA-1000 and Mr. Gamma A2700, had been measured with the developed backscattered photon field to understand energy-dependent features in order to confirm dosemeter readings. Consequently, both scintillator instruments are sensitive for measurements of the relatively low dose rates at 190keV.

Progressive Photon Elimination With a Status Tree

We describe a modified progressive photon mapping (PPM) method applied with sample elimination, referred to as progressive photon elimination, to pursue accurate results and accelerated iterations. Meanwhile, an elimination status tree is proposed for progressive photon elimination, which retains the information used in the elimination and can be updated along with the multi-pass process to solve the challenge of the accuracy of local parameters. By using the status tree, our method can obtain a uniform photon distribution at each iteration by eliminating a certain number of photons. The tree is also improved to adapt to the complicated photon distributions. This strategy also facilitates the parallel elimination with a priori elimination ratio in the status tree, making the algorithm further accelerated. In parallel block processing, the equilibrium and edge problems are resolved. The experimental results show that our method requires about half of the number of iterations to achieve the same visual effect compared with progressive photon mapping.

Highly pure single photon emission from spectrally uniform surface-curvature directed mesa top single quantum dot ordered array

Realizing ordered and spectrally uniform single photon source arrays integrable on-chip with light manipulating elements in a scalable architecture lies at the core of building monolithic quantum optical circuits (QOCs). We demonstrate here a spatially ordered 5 × 8 array of surface-curvature driven mesa-top GaAs(001)/InGaAs/GaAs single quantum dots (MTSQDs) that exhibit highly pure (∼99%) single photon emission as deduced from the measured g(2)(0) < 0.02 at 9.4 K. Polarization-independent and polarization-resolved high resolution photoluminescence measurements show that these ordered and spectrally uniform QDs have neutral exciton emission with an intrinsic linewidth ∼ 10 μeV and a fine structure splitting <10 μeV, an important figure of merit for the use of QDs in QOCs. The findings point to the high potential of using such MTSQD based single photon source arrays as a promising platform for on-chip scalable integration with light manipulating units (connected resonant cavity, waveguide, beam splitter, etc.) to enable constructing QOCs.

Multiple photon effective Hamiltonians in linear quantum optical networks

Abstract We give an alternative derivation for the explicit formula of the effective Hamiltonian describing the evolution of the quantum state of any number of photons entering a linear optics multiport. The description is based on the effective Hamiltonian of the optical system for a single photon and comes from relating the evolution in the Lie group that describes the unitary evolution matrices in the Hilbert space of the photon states to the evolution in the Lie algebra of the Hamiltonians for one and multiple photons. Our derivation complements previous results with a point of view which reminds of the Schrodinger picture. These group theory results allow us to prove that quantum optical linear networks obey different proportionality rules which relate the expected photon number at each input and output ports. In particular, we show that for a uniform photon input the average photon number at the output is preserved for any linear multiport.

Mice and the A-Bomb: Irradiation Systems for Realistic Exposure Scenarios.

Validation of biodosimetry assays is normally performed with acute exposures to uniform external photon fields. Realistically, exposure to a radiological dispersal device or reactor leak will include exposure to low dose rates and likely exposure to ingested radionuclides. An improvised nuclear device will likely include a significant neutron component in addition to a mixture of high- and low-dose-rate photons and ingested radionuclides. We present here several novel irradiation systems developed at the Center for High Throughput Minimally Invasive Radiation Biodosimetry to provide more realistic exposures for testing of novel biodosimetric assays. These irradiators provide a wide range of dose rates (from Gy/s to Gy/week) as well as mixed neutron/photon fields mimicking an improvised nuclear device.

Mesa-top quantum dot single photon emitter arrays: Growth, optical characteristics, and the simulated optical response of integrated dielectric nanoantenna-waveguide systems

Nanophotonic quantum information processing systems require spatially ordered, spectrally uniform single photon sources (SPSs) integrated on-chip with co-designed light manipulating elements providing emission rate enhancement, emitted photon guidance, and lossless propagation. Towards this goal, we consider systems comprising an SPS array with each SPS coupled to a dielectric building block (DBB) based multifunctional light manipulation unit (LMU). For the SPS array, we report triggered single photon emission from GaAs(001)/InGaAs single quantum dots grown selectively on top of nanomesas using the approach of substrate-encoded size-reducing epitaxy (SESRE). Systematic temperature and power dependent photoluminescence (PL), PL excitation, time-resolved PL, and emission statistics studies reveal high spectral uniformity and single photon emission at 8 K with g(2)(0) of 0.19 ± 0.03. The SESRE based SPS arrays, following growth of a planarizing overlayer, are readily integrable with LMUs fabricated subsequently using either the 2D photonic crystal approach or, as theoretically examined here, DBB based LMUs. We report the simulated optical response of SPS embedded in DBB based nanoantenna-waveguide structures as the multifunctional LMU. The multiple functions of emission rate enhancement, guiding, and lossless propagation are derived from the behavior of the same collective Mie resonance (dominantly magnetic) of the interacting DBB based LMU tuned to the SPS targeted emission wavelength of 980 nm. The simulation utilizes an analytical approach that provides physical insight into the obtained numerical results. Together, the combined experimental and modelling demonstrations open a rich approach to implementing co-designed on-chip integrated SPS-LMUs that, in turn, serve as basic elements of integrated nanophotonic information processing systems.

Analysis of the average photon path length between two consecutive reflections from the cavity walls.

In this paper a general theoretical analysis of the average photon path length between two consecutive photon reflections from the cavity walls has been presented. The presented analysis relies only on the energy conservation law and the assumption of the uniform photon distribution within the cavity volume. The obtained general result coincides with the solution previously obtained but under more stringent conditions.

Monte-Carlo simulations of Al2O3 dosimetry in uniform MV photon beams: Influence of field and detector size

This work was to evaluate the absorbed dose to different sizes Al 2 O 3 dosimeter in uniform MV photon beams using Monte Carlo simulation. The absorbed dose ratio factor f md of Al 2 O 3 dosimeters was calculated. The incident beams included 4 MV–24 MV X-rays using Mohan's spectra with different field sizes. Results show that the maximum variation of f md due to different dosimeter sizes is 5%. As the field diameter increases from 1 cm to 3 cm, the difference of f md can be up to 8%. The results of this work show that the effect of dosimeter size and the field size can't be neglected when using Al 2 O 3 dosimeter. ► Evaluate the absorbed dose to Al 2 O 3 dosimeter for radiotherapy beams. ► The effect of dosimeter size and field size can't be neglected. ► More attention should be paid when using an Al 2 O 3 dosimeter in small field.

On the integrating cavity transfer function and decay time

A novel method for deriving the integrating cavity transfer function, where the average electromagnetic radiation intensity decay time in the cavity has been found as the final result, is presented, and where a uniform photon distribution inside the cavity was assumed. Instead of the beam reflection analysis, the method is based on employing the energy conservation law inside the integrating cavity. The obtained result for the decay time is slightly different from other results obtained elsewhere but still in relatively good agreement with them. In order to verify the obtained result, we performed a similar analysis based on the photon number conservation law. This analysis gives the same result for the decay time as the first one. Finally, in order to confirm the obtained result, we statistically analyzed the average lifetime of a photon inside the cavity after the radiation source switch-off, i.e. the average time between the radiation source switch-off and its absorption by the cavity inner walls. The result for the decay time obtained in this way is identical to the results obtained using the above-presented methods. At the end, the transfer function of the integrating cavity filled with a weak absorbing material is derived. Based on the obtained result, a novel method for the absorption coefficient measurement is proposed.

Noninvasive Monitoring of Placenta-Specific Transgene Expression by Bioluminescence Imaging

BackgroundPlacental dysfunction underlies numerous complications of pregnancy. A major obstacle to understanding the roles of potential mediators of placental pathology has been the absence of suitable methods for tissue-specific gene manipulation and sensitive assays for studying gene functions in the placentas of intact animals. We describe a sensitive and noninvasive method of repetitively tracking placenta-specific gene expression throughout pregnancy using lentivirus-mediated transduction of optical reporter genes in mouse blastocysts.Methodology/Principal FindingsZona-free blastocysts were incubated with lentivirus expressing firefly luciferase (Fluc) and Tomato fluorescent fusion protein for trophectoderm-specific infection and transplanted into day 3 pseudopregnant recipients (GD3). Animals were examined for Fluc expression by live bioluminescence imaging (BLI) at different points during pregnancy, and the placentas were examined for tomato expression in different cell types on GD18. In another set of experiments, blastocysts with maximum photon fluxes in the range of 2.0E+4 to 6.0E+4 p/s/cm2/sr were transferred. Fluc expression was detectable in all surrogate dams by day 5 of pregnancy by live imaging, and the signal increased dramatically thereafter each day until GD12, reaching a peak at GD16 and maintaining that level through GD18. All of the placentas, but none of the fetuses, analyzed on GD18 by BLI showed different degrees of Fluc expression. However, only placentas of dams transferred with selected blastocysts showed uniform photon distribution with no significant variability of photon intensity among placentas of the same litter. Tomato expression in the placentas was limited to only trophoblast cell lineages.Conclusions/SignificanceThese results, for the first time, demonstrate the feasibility of selecting lentivirally-transduced blastocysts for uniform gene expression in all placentas of the same litter and early detection and quantitative analysis of gene expression throughout pregnancy by live BLI. This method may be useful for a wide range of applications involving trophoblast-specific gene manipulations in utero.

SU-GG-I-19: Improving the HU Accuracy of Varian's OBI CBCT

Purpose: Varian's OBI CBCT has been widely used for IGRT and adaptive radiotherapy. But studies showed that the Hounsfield unit (HU) accuracy in CBCT was still poor due to the residual scatter after the 1D anti‐scatter grid. This work was trying to improve the HU accuracy by correcting the residual scatter.Method and Materials:CBCT projections of both a Quasar and a Catphan phantom were acquired in half fan mode using a half‐bowtie filter. However, the bowtie filter causes non‐uniform fluence and uneven beam hardening before irradiating the phantom. Our recently published scatter correction algorithm was based on uniform photon fluence with a single x‐ray spectrum across the beam. In order to do scatter correction in this scenario, the non‐uniform fluence was corrected by using a single open projection in air with the bowtie. Also, Monte Carlo generated energy spectra after the bowtie filter was used to compensate for the effect of non‐even beam hardening. Finally, image reconstruction was made using the FDK algorithm from the scatter corrected projections. Results: For the Quasar phantom, the HU of CBCT for the acrylic and bone inserts were 180, 265 HU from our approach, 27 and 59 HU from the CBCT reconstructor, while from planning CT, they were 127 and 270 HU respectively. For the CatPhan phantom, the HU of CBCT for the acrylic bone and air inserts were 139, 806 and −667 HU from our approach, −242, 322 and −756 HU from the CBCT reconstructor, while from planning CT, they were 81, 856 and −934 HU respectively. Conclusion: In this preliminary study, the HU accuracy of CBCT was substantially improved from our study compared to those from Varian's online reconstruction for most of the materials. However, there is still difference for air cavity from the planning CT, which needs further investigation.

A STUDY OF SOLID STATE LASER PASSIVE OPTICAL Q-SWITCHING OPERATION REGIME (Part 1)

This paper is the first of a four series treating, theoretically with experimental comparison, the issue of solid state laser passive optical Q-switching regime. In this first paper the technique of solid state lasers passive optical Q-switching is numerically investigated considering the case of longitudinally and transversally uniform photon, population inversion and absorption centres densities. The coupled differential equations defining photon, population inversion and absorption centres densities are numerically solved being the basis of passively optical Q-switched laser functional simulation. The numerical simulations are performed using the several software packages, mostly SCILAB programs. The developed SCILAB programs can be used for a large range of saturable absorption centre and active media parameters, mainly the initial (low signal) optical transmittance of the passive optical Q-switch. The developed FORTRAN and SCILAB programs can be applied for passively Q-switched solid state lasers of several types emitting at several NIR wavelengths, in domain 1 ÷ 2 μm. For validating the numerical simulation results are compared with The results of the numerical simulation are compared with experimentally obtained ones, in the case of a LiF:F2 passively Q-switched Nd:YAG. A good agreement between the two kinds of results is observed.

The Influence of Zn-Diffusion Depth on the Static and Dynamic Behavior of Zn-Diffusion High-Speed Vertical-Cavity Surface-Emitting Lasers at an 850 nm Wavelength

We studied the static and dynamic performance of high-speed Zn-diffusion vertical-cavity surface-emitting lasers (VCSELs) (at an 850-nm optical wavelength) as affected by different Zn-diffusion depths. Device A has the largest Zn-diffusion depth (~1.3 mum) and can sustain single-mode operations under a whole range of bias currents, exhibiting the largest differential quantum efficiency and smallest far-field divergence angle. Devices B and C have smaller Zn-diffusion depths (0.5 mum for device B and 0 mum for device C) and exhibit poorer multimode performance. However, due to the serious spatial hole burning effect of device A, induced by its single-spot and high-power output, the measured electrical-to-optical (EO) frequency response of device A shows a more serious (>3 dB) low-frequency (<2 GHz) rolloff than does that of the other two devices. Although device B (with a shallow Zn-diffusion depth) shows multimode performance, with it we can minimize the low-frequency roll-off problem, due to its more uniform photon density distribution and less spatial-hole burning effect than that of device A. Using device B, we can achieve an 11-GHz 3-dB bandwidth, the highest modulation current efficiency ( ~ 8 GHz/mA1/2), and clear eye-opening at 10 Gb/s operation, with the lowest dc and radio frequency power consumption among the three devices. These measurement results indicate that the dynamic and static performance of high-speed VCSELs can be optimized by controlling the Zn-diffusion depth, and manipulating the number of optical modes in the VCSEL cavity.

Quantitative photoacoustic tomography from boundary pressure measurements: noniterative recovery of optical absorption coefficient from the reconstructed absorbed energy map

We describe a noniterative method for recovering optical absorption coefficient distribution from the absorbed energy map reconstructed using simulated and noisy boundary pressure measurements. The source reconstruction problem is first solved for the absorbed energy map corresponding to single- and multiple-source illuminations from the side of the imaging plane. It is shown that the absorbed energy map and the absorption coefficient distribution, recovered from the single-source illumination with a large variation in photon flux distribution, have signal-to-noise ratios comparable to those of the reconstructed parameters from a more uniform photon density distribution corresponding to multiple-source illuminations. The absorbed energy map is input as absorption coefficient times photon flux in the time-independent diffusion equation (DE) governing photon transport to recover the photon flux in a single step. The recovered photon flux is used to compute the optical absorption coefficient distribution from the absorbed energy map. In the absence of experimental data, we obtain the boundary measurements through Monte Carlo simulations, and we attempt to address the possible limitations of the DE model in the overall reconstruction procedure.