High Spectral Brightness Research Articles

Intermediate state between a solitary singlet and a molecule in lasers

As an important tool in science and industry, the ultrafast fiber laser has two paradigmatic pulse regimes of the single-soliton (SS) and the soliton molecule (SM), which have been individually researched thoroughly. However, the mutual transformation between two states is a fuzzy problem with significance in understanding the soliton dynamics and actively manipulating lasing states. Here, we reveal an intermediate state that spontaneously switches between SS and SM without external triggering in experiments and simulations. Two critical processes dominating the switching are the soliton splitting and SM partial annihilation, which are found to be induced by the high-order soliton effect and spontaneous symmetry breaking, respectively. Moreover, statistics of this intermediate state reveal the spectral rogue waves induced by the SM with high spectral brightness. This work sheds light on the switching dynamics between nonlinear states in the out-of-equilibrium systems, and has potential for intelligent manipulation of lasing states.

Bright narrowband photon pairs generated in an intra-cavity 2N walk-off compensating configuration

We studied theoretically the influence of the walk-off effect on the spectral brightness of the type-I cavity-enhanced spontaneous parametric down-conversion. The results show that the spectral brightness of the generated entangled photon pairs can be improved significantly by using a 2N walk-off compensating configuration, in which N pairs of nonlinear crystals with their walk-off angles of opposite signs are stacked and bonded in sequence along the propagation direction. The spectral brightness of the entangled photon pairs are expected theoretically to be 1.27×105 pairs/(smWMHz) for N = 4 with a submegahertz bandwidth in a triple-resonant cavity configuration. Our results provide a solid theoretical basis for the generation of entangled photon-pair sources of high spectral brightness and narrow bandwidth, which may have potential applications in quantum technology.

Intensity correlation functions of microwave maser sources

Abstract Astrophysical sources of microwave radiation with extremely high spectral brightness are interpreted as masers. But by itself, the information about high brightness of radiation does not make it possible to establish whether the radiation is thermal or maser. This can be determined only on the basis of the analysis of high-order correlation functions. A possible measurement procedure for the second-order autocorrelation function (the bunching parameter) for these sources is proposed.

Integrated Si3N4 microresonator-based quantum light sources with high brightness using a subtractive wafer-scale platform.

The silicon nitride (Si3N4) platform, demonstrating a moderate third-order optical nonlinearity and a low optical loss compared with those of silicon, is suitable for integrated quantum photonic circuits. However, it is challenging to develop a crack-free, wafer-scale, thick Si3N4 platform in a single deposition run using a subtractive complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process suitable for dispersion-engineered quantum light sources. In this paper, we demonstrate our unique subtractive fabrication process by introducing a stress-release pattern prior to the single Si3N4 film deposition. Our Si3N4 platform enables 950 nm-thick and 8 μm-wide microring resonators supporting whispering-gallery modes for quantum light sources at 1550 nm wavelengths. We report a high photon-pair generation rate of ∼1.03 MHz/mW2, with a high spectral brightness of ∼5×106 pairs/s/mW2/GHz. We demonstrate the first heralded single-photon measurement on the Si3N4 platform, which exhibits a high quality of conditional self-correlation gH(2)(0) of 0.008 ± 0.003.

Thermal emission measurements of ordinary chondrite mineral analogs in a simulated asteroid environment: 1. Constituent mineral phases

Telescopic surveys suggest that S-type asteroids are the dominant small body type in the near-Earth object population and are among the most abundant in the inner main asteroid belt. Given the link between S-type asteroids and the ordinary chondrites, regoliths of ordinary chondrite mineralogy may represent the most common regolith type on small bodies in these populations, and therefore it is important to understand the thermal emission properties of ordinary chondrite mineral analogs radiating into asteroid-like environments. Thermal infrared spectra of particulate surfaces in airless environments are substantially modified due to near-surface thermal gradients formed between the immediate surface undergoing radiative cooling and underlying materials that are warmed by the absorption of solar radiation. To advance our understanding of how the thermal emission properties of materials relevant to ordinary chondrite composition may be modified in an airless environment, we analyze a suite of analogous single mineral phases in a simulated asteroid surface environment. A companion paper presents and discusses analyses of modal mixtures of these minerals designed to match modal abundances of ordinary chondrites as reported in the literature. We probe the thermal emission of these materials by investigating relationships between their sample temperatures, emissivity spectra, brightness temperatures, and the environmental and experimental conditions. We focus attention on the radiance spectra of the samples as derived by two data reduction methods and their corresponding brightness temperature spectra to infer the intensity of near-surface thermal gradients formed in the samples. We demonstrate that the Christiansen feature position is sensitive to the sample cup temperature with data collected in a simulated asteroid environment under constant illumination condition. Through the analysis of particulate samples of three particle size ranges (<25 μm, 25–125 μm, and 125–250 μm) at ambient and cold, vacuum conditions, we demonstrate that thermal gradients form as a result of the physical, environmental, and optical properties of the target surface. Using temperature variations observed in high spectral resolution brightness temperature spectra as a proxy for the near-surface thermal gradients, we observe relationships between the intensity of the thermal gradient and the sample particle size. Modifications of iron metal spectra due to the changing environmental conditions are examined and compared with the silicate data. Implications for the measurement of thermal infrared spectra of metal-bearing planetary materials, such as the ordinary chondrites, are discussed.

Tunable low-coherence light source with high spectral brightness

Operation of a tunable tandem-type low-coherence light source with high spectral brightness based on commercially available optical elements (superluminescent diode, semiconductor optical amplifier, and bulk dwiffraction grating) is studied experimentally. A unique combination of the output source characteristics, namely, a spectral power density of 36 mW nm−1, a wavelength tuning range of 35 nm (834 – 869 nm), and a more than 20-dB excess of the central peak intensity over the superluminescent pedestal, is experimentally obtained. It is shown that the output radiation spectrum with a width of 1.4 nm has a smooth bell-shaped profile with side lobes lying below the superluminescent pedestal. It is proved that such a light source is of practical interest for various applications.

Multidimensional Entanglement Generation with Multicore Optical Fibers

Trends in photonic quantum information follow closely the technical progress in classical optics and telecommunications. In this regard, advances in multiplexing optical communications channels have also been pursued for the generation of multi-dimensional quantum states (qudits), since their use is advantageous for several quantum information tasks. One current path leading in this direction is through the use of space-division multiplexing multi-core optical fibers, which provides a new platform for efficiently controlling path-encoded qudit states. Here we report on a parametric down-conversion source of entangled qudits that is fully based on (and therefore compatible with) state-of-the-art multi-core fiber technology. The source design uses modern multi-core fiber beam splitters to prepare the pump laser beam as well as measure the generated entangled state, achieving high spectral brightness while providing a stable architecture. In addition, it can be readily used with any core geometry, which is crucial since widespread standards for multi-core fibers in telecommunications have yet to be established. Our source represents an important step towards the compatibility of quantum communications with the next-generation optical networks.

Refractive Guide Switching a Regenerative Amplifier Free-Electron Laser for High Peak and Average Power Hard X Rays.

We present an x-ray regenerative amplifier free-electron laser design capable of producing fully coherent hard x-ray pulses across a broad tuning range at a high steady state repetition rate. The scheme leverages a strong undulator taper and an apertured diamond output-coupling cavity crystal to produce both high peak and average spectral brightness radiation that is 2 to 3 orders of magnitude greater than conventional single-pass self-amplified spontaneous emission free-electron laser amplifiers. Refractive guiding in the postsaturation regime is found to play a key role in passively controlling the stored cavity power. The scheme is explored both analytically and numerically in the context of the Linac Coherent Light Source II High Energy upgrade.

Mid-infrared resonant cavity light emitting diodes operating at 4.5 µm.

We report on a mid-infrared resonant cavity light emitting diode (RCLED) operating at the wavelength of 4.5 µm with a narrow spectral linewidth at room temperature. Compared to a reference LED without a resonant cavity, our RCLED exhibits (85x) higher peak intensity, (13x) higher integrated output power, (16x) narrower spectral linewidth and (7x) superior temperature stability. The device consists of a one-wavelength thick micro-cavity containing an Al0.12In0.88As/InAs0.85Sb0.15 quantum well active region sandwiched between two high contrast AlAs0.08Sb0.92/GaSb distributed Bragg reflector mirrors, grown lattice-matched on GaSb by molecular beam epitaxy. The high spectral brightness, narrow linewidth and superior temperature stability are attractive features, enabling these devices to be used for detection of N2O at 4.5 µm. We show that with only minor adjustments the gases CO2 (4.2 µm) and CO (4.6 µm) are also readily accessible.

Impact of water-soluble 2D CdSe/CdS nanoplatelets on seed germination and early growth in Vigna radiata

Cadmium chalcogenides nanoplatelets are two-dimensional semiconductor nanocrystals exhibiting high spectral brightness and unique size-dependent properties. CdSe/CdS nanoplatelets (NPLs) display potential as promising candidates for the light emission diode (LED), sensors, photovoltaics, and bioimaging. However, the environmental fate of the nanoplatelets raises a potential threat to living systems. To address the concern, we have synthesized the CdSe/CdS NPLs using the colloidal atomic layer deposition (cALD) method followed by surface modification with 2-mercaptoethanol to introduce water solubility. The TEM and XRD analysis confirmed a zinc blend crystal structure at the nanometer scale. The nanoplatelets negatively affected various germination parameters, plant height, and weight in Vigna radiata. The nanoplatelets instigated the phytotoxicity in root and shoot tissues in early plant growth. It also severely devastated the stress tolerance capabilities in the plant system. The damages incurred by the nanoplatelets were also confirmed by estimating the levels of plant antioxidant enzymes. The catalase enzyme activity was upshot in response to excessive levels of reactive oxygen species level triggered by nanoplatelets and cadmium exposure. Surprisingly, the peroxidases enzyme activities were substantially reduced due to toxicity induced by the nanomaterials and cadmium. The nanoplatelets, despite the confinement of cadmium and selenium in the nanostructure, could negatively impact plant growth and development. Our results showed that unique shape, small size, and oxidative nature of the nanomaterial enabled manifold destructions in the Vigna radiata. Therefore, we urge a proper regulation for the large-scale synthesis and utilization of the CdSe/CdS NPL.

Water-dispersed semiconductor nanoplatelets with high fluorescence brightness, chemical and colloidal stability.

Quasi-two dimensional semiconductor nanoplatelets (NPLs) exhibit high spectral brightness and large absorption cross sections, making them promising for various applications including bioimaging. However, the synthesis of NPLs takes place in organic solvents, therefore they require phase transfer in order to use them in aqueous environments. The phase transfer of NPLs has so far been challenging with few examples in literature. This is likely due to the facile agglomeration of materials with plate-like geometries during the coating procedure. Here we demonstrate how to overcome agglomeration and transfer NPLs, individually coated with amphiphilic polymer chains, to aqueous phase. Upon one and two-photon excitation the water transferred NPLs exhibit more than two fold higher fluorescent brightness relative to commercially available quantum dots. Additionally, the polymer coating increase the stability of nanoparticles in physiological conditions (pH 4.5-7.4, [NaCl] 5.8-11.7 g L-1, and in human serum). Our experiments with NPL labeled RAW264.7 cells demonstrate the capabilities of NPLs as next generation ultra-bright fluorescent labels for bioimaging.

Electroluminescence enhancement in mid-infrared InAsSb resonant cavity light emitting diodes for CO2 detection

In this work, we demonstrated a mid-infrared resonant cavity light emitting diode (RCLED) operating near 4.2 μm at room temperature, grown lattice-matched on a GaSb substrate by molecular beam epitaxy, suitable for CO2 gas detection. The device consists of a 1λ-thick microcavity containing an InAs0.90Sb0.1 active region sandwiched between two high contrast, lattice–matched AlAs0.08Sb0.92/GaSb distributed Bragg reflector (DBR) mirrors. The electroluminescence emission spectra of the RCLED were recorded over the temperature range from 20 to 300 K and compared with a reference LED without DBR mirrors. The RCLED exhibits a strong emission enhancement due to resonant cavity effects. At room temperature, the peak emission and the integrated peak emission were found to be increased by a factor of ∼70 and ∼11, respectively, while the total integrated emission enhancement was ∼×33. This is the highest resonant cavity enhancement ever reported for a mid-infrared LED operating at this wavelength. Furthermore, the RCLED also exhibits a superior temperature stability of ∼0.35 nm/K and a significantly narrower (10×) spectral linewidth. High spectral brightness and temperature stable emission entirely within the fundamental absorption band are attractive characteristics for the development of next generation CO2 gas sensor instrumentation.

Triple-State Dissipative Soliton Laser Via Ultrafast Self-Parametric Amplification

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Chip-integrated visible-telecom photon pair sources for quantum communication.

Photon pair sources are fundamental building blocks for quantum entanglement and quantum communication. Recent studies in silicon photonics have documented promising characteristics for photon pair sources within the telecommunications band, including sub-milliwatt optical pump power, high spectral brightness, and high photon purity. However, most quantum systems suitable for local operations, such as storage and computation, support optical transitions in the visible or short near-infrared bands. In comparison to telecommunications wavelengths, the significantly higher optical attenuation in silica at such wavelengths limits the length scale over which optical-fiber-based quantum communication between such local nodes can take place. One approach to connect such systems over fiber is through a photon pair source that can bridge the visible and telecom bands, but an appropriate source, which should produce narrow-band photon pairs with a high signal-to-noise ratio, has not yet been developed. Here, we demonstrate an on-chip visible-telecom photon pair source for the first time, using high quality factor silicon nitride microresonators to generate bright photon pairs with an unprecedented coincidence-to-accidental ratio (CAR) up to (3.8 ± 0.2) × 103. We further demonstrate dispersion engineering of the microresonators to enable the connection of different species of trapped atoms/ions, defect centers, and quantum dots to the telecommunications bands for future quantum communication systems.

Efficient Raman converter in the yellow range with high spatial and spectral brightness.

We present a Raman converter emitting at 583nm on the second Stokes order of a line of propan-2-ol pumped by a microlaser at 532nm in the sub-nanosecond regime. We used a mixture of liquids to adapt the transmission band of a photonic bandgap fiber. The internal conversion efficiency is 67% in photon numbers, and the output power is 1.06mW, corresponding to a maximum peak power of 338W. The beam delivered by the converter presents a Gaussian spatial structure and a high spectral brightness, typically more than five times higher than supercontinuum sources in this spectral range.

Mid-infrared octave spanning supercontinuum generation to 85 μm in silicon-germanium waveguides

Efficient on-chip molecule and bio-agent detection can be achieved by accessing strong molecular absorption lines in the mid-infrared, but it requires high output power broadband mid-IR sources. Here, we report supercontinuum generation in an air-clad $Si_{0.6}$$Ge_{0.4}$/Si waveguide that emits a broad spectrum spanning from 3.0 μm to 8.5 μm. These waveguides have anomalous dispersion and low propagation loss (<0.4 dB/cm) in the mid-IR, which leads to a supercontinuum output with a high average power of more than 10 mW on-chip. The realization of broadband mid-IR sources with high spectral brightness makes the SiGe-on-Si platform promising for a wide range of applications.

Silicon photonic entangled photon-pair and heralded single photon generation with CAR &gt; 12,000 and g^(2)(0) &lt; 0006

We report measurements of time-frequency entangled photon pairs and heralded single photons at 1550~nm wavelengths generated using a microring resonator pumped optically by a diode laser. Along with a high spectral brightness of pair generation, the conventional metrics used to describe performance, such as Coincidences-to-Accidentals Ratio (CAR), conditional self-correlation [$g^{(2)}(0)$], two-photon energy-time {F}ranson interferometric visibility etc. are shown to reach a high-performance regime not yet achieved by silicon photonics, and attained previously only by crystal, glass and fiber-based pair-generation devices.

Design of a new family of narrow-linewidth mid-infrared lasers

We describe the design of a new family of high spectral brightness narrow linewidth (NLW) mid-infrared (MIR) lasers of < 1 MHz anticipated linewidths with potential for operation at any target wavelength between 2.5 and 9.5 um. More specifically, we analyze the potential performance characteristics of mid-infrared distributed feedback (DFB) Raman fiber lasers (RFLs) based on Pi-phase-shifted (PPS) Fiber Bragg Gratings (FBGs) written in appropriately chosen low-phonon-energy glass fibers. In particular, we calculate anticipated threshold pump powers for optimal laser designs and pump wavelengths for single frequency (fundamental mode) operation of specific mid-infrared DFB-RFLs operating at chosen target wavelengths, and show that these pump powers can be as low as a few milliWatts for MIR DFB-RFLs fabricated with appropriate low-loss small mode area single mode fibers. As such, we clearly establish the PPS-DFB RFL platform as a very practical approach for constructing a broad range of narrow linewidth MIR coherent sources for numerous applications, including proximal and remote sensing of molecules and various high spectral brightness and long coherence length MIR applications.

Robust, high brightness, degenerate entangled photon source at room temperature

We report on a compact, simple and robust high brightness entangled photon source at room temperature. Based on a 30-mm-long periodically-poled potassium titanyl phosphate crystal, the source produces non-collinear, type-0, phase-matched, degenerate photons at 810 nm with spectral brightness as high as ~0.41 ± 0.02 (~0.025 ± 0.02) MHz/mW/nm for multi (single) mode fiber coupling. So far, this is the highest number of degenerate photons generated using a continuous-wave laser pumped bulk crystal and detected using multimode fiber. We have studied the dependence of pump focusing on the brightness of the generated photons collected using both multimode, and single mode fibers. For a fixed pump power and crystal parameters, the SPDC source has an optimum pump waist radius producing maximum number of paired photons. Combining the crystal in a novel system architecture comprised with Sagnac interferometer and polarizing optical elements, the source produces polarization entangled photon states with high spectral brightness. Even in the absence of any phase compensation, the entangled photon states detected using single mode fiber have a Bell’s parameter, S = 2.63 ± 0.02, violating the Bell’s inequality by nearly 32 standard deviations and fidelity of 0.975. The compact footprint, robust design, and room temperature operation, make our source ideal for various quantum communication experiments.

Energy and Emission Characteristics of a Short-Arc Xenon Flash Lamp Under "Saturated" Optical Brightness Conditions

We present the results of a study of the electrical, energy, and spectral brightness characteristics of an experimental three-electrode high-pressure xenon flash lamp under conditions ensuring close to maximum possible spectral brightness for the xenon emission. We show that under saturated optical brightness conditions (brightness temperature in the visible region of the spectrum ~30,000 K), emission of a pulsed discharge in xenon is quite different from the emission from an ideal blackbody: the maximum brightness temperatures are 24,000 K in the short-wavelength UV region and 19,000 K in the near IR range. The relative fraction of UV radiation in the emission spectrum of the lamp is >50%, which lets us consider such lamps as promising broadband sources of radiation with high spectral brightness for many important practical applications.