High-speed switching of biphoton delays through electro-optic pump frequency modulation
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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Results for “FREQUENCY MODULATION”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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A frequency-modulated continuous-wave reflectometer for the Lithium Tokamak Experiment
Not Available
Kubota, S.↗
Fibre laser system providing generation of frequency-modulated pulses with a spectral width exceeding the gain linewidth
We propose an improved scheme of an amplifier similariton laser with a spectral width of the output significantly exceeding the gain linewidth. In the system, an additional dispersion element is inserted into the cavity to provide a local increase in the peak pulse power. The proposed scheme allows a reduction of pulse duration and an increase in peak power of the output pulse after compression. (paper)
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Self-Powering High Frequency Modulated SiC Power MOSFET Isolated Gate Driver
A novel implementation of an isolated gate driver for power switches is proposed in this study. The driver is bespoke designed for SiC power mosfet s. The proposal achieves the main driver characteristics—isolation capability, gate switching command, and power transfer to the secondary side by using a unique magnetic transformer. The resulting simple circuitry enables the integration of the driver into the power cell, achieving theoretical higher power density values of the final system. The principle of operation of the driver is described in detail. The original pulsewidth modulation signal is modulated with a pure ac square waveform under a two-level modulation scheme, that guarantees no saturation of the magnetic core. Here, the signal is then magnetically coupled to the secondary side, where it is rectified and reconstructed to effectively drive the target device. In addition, the steps needed to provide a suitable design taking into account the parameters of the target power switch are also detailed. The resulting driver is characterized and a prototype of the driver is built and tested. The main results of the driver performance on a SiC mosfet -based prototype are presented. Based on the analysis of these results, this study experimentally demonstrates the feasibility of the proposal.
25 ENERGY STORAGE↗
An architecture for pre-warping general parametric frequency-modulated radar waveforms.
Abstract not provided.
Doerry, Armin W.↗
Compact laser source with frequency modulators generating multiple lines
A compact laser source and a single sideband modulator used therein is disclosed. The compact laser source includes a seed laser and one or more channels, with each channel generating one or more output laser beams having corresponding different wavelengths. The compact laser source can be formed in whole or in part on a single optical motherboard to thereby minimize space and power requirements. By employing the disclosed single sideband modulator, harmonics in the generated output laser beams can be minimized. The compact laser source finds application in an atom interferometer (AI) system, which may be used to measure gravity, acceleration, or rotation of the AI system.
Lentine, Anthony L.↗
Energy Consumption for High-Frequency Switching of a Quantum-Dot Microdisk Laser
We have studied characteristics of a 23-μm-diameter microdisk laser operating in a regime of direct high-frequency modulation at a stabilized heat-sink temperature of 18°C. It is found that the minimum energy consumption in this regime amounts to ~1.6 pJ/bit and is achieved at a modulation frequency of 4.2 GHz. The maximum modulation frequency is 6.7 GHz, at which the minimum energy consumption is 3.3 pJ/bit.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Spin polarization of {sup 87}Rb atoms with ultranarrow linewidth diode laser: Numerical simulation
In order to polarize {sup 87}Rb vapor effectively with ultranarrow linewidth diode laser, we studied the polarization as a function of some parameters including buffer gas pressure and laser power. Moreover, we also discussed the methods which split or modulate the diode laser frequency so as to pump the two ground hyperfine levels efficiently. We obtained some useful results through numerical simulation. If the buffer gas pressure is so high that the hyperfine structure is unresolved, the polarization is insensitive to laser frequency at peak absorption point so frequency splitting and frequency modulation methods do not show improvement. At low pressure and laser power large enough, where the hyperfine structure is clearly resolved, frequency splitting and frequency modulation methods can increase polarization effectively. For laser diodes, frequency modulation is easily realized with current modulation, so this method is attractive since it does not add any other components in the pumping laser system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Active region of a functionally integrated laser – modulator
A method for the functional integration of injection lasers and modulators of generated light in a single heterostructure with spatially displaced quantum wells in the conduction and valence bands, formed by the second-type heterojunctions, is proposed. The structures and energy band diagrams of the active regions of functionally integrated lasers – modulators with amplitude and frequency modulation are considered. A physical – topological model and a technique for numerical simulation of lasers – modulators is proposed. It is shown that the maximum modulation frequencies for the proposed heterostructures, in contrast to the same frequencies implemented under pump current modulation, are not limited by the duration of transients in the laser power supply circuit and the carrier lifetime in the laser active region but are determined by the photon lifetime in the cavity. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
A Laser Frequency Transverse Modulation Might Compensate for the Spectral Broadening Due to Large Electron Energy Spread in Thomson Sources
Compact laser plasma accelerators generate high-energy electron beams with increasing quality. When used in inverse Compton backscattering, however, the relatively large electron energy spread jeopardizes potential applications requiring small bandwidths. We present here a novel interaction scheme that allows us to compensate for the negative effects of the electron energy spread on the spectrum, by introducing a transverse spatial frequency modulation in the laser pulse. Such a laser chirp, together with a properly dispersed electron beam, can substantially reduce the broadening of the Compton bandwidth due to the electron energy spread. We show theoretical analysis and numerical simulations for hard X-ray Thomson sources based on laser plasma accelerators.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
High performance graphene-like thinly layered graphite based visible light photodetector
In this work, the drop casting method is utilized to obtain a thin graphene-like graphite layer as a photodetection layer on a SiO{sub 2}/Si substrate, and its performance is characterized to determine its potential use in commercial applications. The thin layer is formed by first synthesizing graphite soot from a butane flame before being turned into a liquid solution and drop-casted onto the substrate to form a thin graphene-like graphite film. Field emission scanning electron microscope and Raman vibrational mode analyses indicate that the fabricated graphene-like graphite layer has characteristics similar to the graphene. The graphene-like graphite photodetector demonstrates a narrow photoresponse from 530 to 680 nm, covering visible sources from green to red. The responsivity and external quantum efficiency of the device under the illumination of red laser 660 nm is found to be around 148 mA W{sup −1} and 27.8% respectively and is faster than that reported for similar systems using graphene and reduced graphene oxide previously. A fast response time of 83.7 and 28 µs at a modulation frequency of 1.0 and 10000 Hz respectively from the graphene-like thinly layered graphite photodetector shows potential application for the development of low-cost carbon-based photodetectors in near future.
77 NANOSCIENCE AND NANOTECHNOLOGY↗
Piezoelectric deformable photonic devices
A CMOS-compatible actuator platform for implementing phase, amplitude, and frequency modulation in silicon nitride photonic integrated circuits via piezo-optomechanical coupling using tightly mechanically coupled aluminum nitride actuators is disclosed. The platform, which may be fabricated in a CMOS foundry, enables scalable active photonic integrated circuits for visible wavelengths, and the piezoelectric actuation functions without performance degradation down to cryogenic operating temperatures. A number of devices are possible, including ring modulator devices, phase shifter devices, Mach-Zehnder interferometer devices, directional coupler devices (including tunable directional coupler devices), and acousto-optic modulator and frequency shifter devices, each of which can employ the same AlN actuator platform. As all of these devices can be built on the same AlN actuator platform, numerous optical functions can be implemented on a single die.
Eichenfield, Matt↗
Precise modulation of laser radiation by an acousto-optic modulator for stabilisation of the Nd : YAG laser on optical resonances in molecular iodine
A system of precise frequency modulation of laser radiation by an acousto-optic modulator, which makes it possible to stabilise the radiation power and simultaneously suppress the residual amplitude modulation to a level of 10{sup -8} of the total laser power at the third harmonic of modulation frequency (∼500 Hz), is presented. The use of this system for the Nd : YAG/I{sub 2} optical frequency standard and application of digital signal synthesis and processing methods provided a level of frequency standard instability as small as ∼10{sup -15} for ∼6 × 10{sup 4} s. (frequency standards)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients
We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement.
43 PARTICLE ACCELERATORS↗
Nanoscale Compositional and Strain Gradients Enable High‐Speed and Amplitude‐Resolved Pyroelectric Sensing
The frequency response of pyroelectric sensors is fundamentally governed by thermal time constant (τth, determined by thermal mass and thermal conductance) and electrical impedance arising from film capacitance and readout circuit. Conventional bulk LiTaO3 detectors are optimized for high responsivity at low modulation frequencies (0.1-10 Hz), possessing a large τth that thermally averages rapid temperature oscillations at elevated modulation frequencies, limiting fidelity in resolving dynamic varying thermal signals. Here, compositional and strain gradients are introduced into 100-nm-thick relaxor-ferroelectric films reducing τth to ≈2 µs and producing built-in potentials (≈1.45 V or 145 kV cm-1) that enhance the pyroelectric coefficient and suppress the dielectric constant. This enables complementary dual-mode operation by enhancing current-mode electrical responsivity and improving the voltage-mode figure of merit - advantageous for superior temperature resolution (ΔTmin ≈ 30 µK). The responsivity peak shifts to near 1 kHz (>2500-times higher than conventional bulk sensors), with measurable responsivity extending to a carrier frequency of 100 kHz and amplitude-resolved detection at modulation frequencies up to 15 kHz. These results establish nanoscale internal-field engineering can reshape electro-thermal trade-off in pyroelectric thin films toward zero-bias, high-thermal-sensitivity, and amplitude-resolved thermal sensing across a wide frequency bandwidth.
Lin, Ching‐Che↗
Capability of Impedance Measurement Using Spread Spectrum Time-Domain Reflectometry
Spread spectrum time-domain reflectometry (SSTDR) has been proposed for measuring electrical impedance on live, energized systems, in electrically noisy environments, or for measuring multiple channels simultaneously. Here we evaluate the capability of SSTDR for impedance measurement from near dc to 96 MHz and find that they agree very well with measurements from a vector network analyzer (VNA). Time gating is used to remove (calibrate out) transmission line effects. We evaluate the frequency ranges over which SSTDR at different modulation frequencies is accurate for the measurement of series resistive–capacitive ( RC ) loads and observe that fusing measurements from multiple modulation frequencies can broaden the effective measurement bandwidth.
14 SOLAR ENERGY↗