Effect Of Intensity Modulation Research Articles

Influence of light source modulation on detection performance of trace-level SF6 fault gas using photoacoustic spectroscopy

Photoacoustic spectroscopy (PAS) is highly valued in gas detection for its outstanding sensitivity and rapid response. Addressing its limited precision in trace gas analysis, scholars have taken numerous measures to optimize structural and modify the size of acoustic sensors and photoacoustic cells (PACs). Nevertheless, advancements in laser modulation remain understudied due to technical difficulties. This paper theoretically examines the effects of intensity modulation with square wave signals and wavelength modulation involving sawtooth and sinusoidal. In this paper, a theoretical approach is proposed to examine the effects of intensity modulation with square wave signals and wavelength modulation involving sawtooth and sinusoidal signals. Experimental measurements were performed using parameters obtained in preliminary experiments. We constructed an experimental setup with varied-length PACs to bolster experimental dependability, focusing on H2S as the target gas to compare the two laser modulation techniques. The results exhibited that at low frequencies, intensity modulation outperforms wavelength modulation. At resonance frequencies, however, wavelength modulation could provide stronger signals’ intensity. Modulation frequency considerations are therefore crucial when choosing a modulation method for PAS gas detection. Without specific frequency requirements, a second harmonic modulation at resonance is recommended. This study provides guidance on selecting laser modulation methods for PAS, potentially refining the technique’s application in trace gas analysis.

Soft Optomechanical Systems for Sensing, Modulation, and Actuation

AbstractSoft optomechanical systems have the ability to reversibly respond to optical and mechanical external stimuli by changing their own properties (e.g., shape, size, viscosity, stiffness, color or transmittance). These systems typically combine the optical properties of plasmonic, dielectric or carbon‐based nanomaterials with the high elasticity and deformability of soft polymers, thus opening the path for the development of new mechanically tunable optical systems, sensors, and actuators for a wide range of applications. This review focuses on the recent progresses in soft optomechanical systems, which are here classified according to their applications and mechanisms of optomechanical response. The first part summarizes the soft optomechanical systems for mechanical sensing and optical modulation based on the variation of their optical response under external mechanical stimuli, thereby inducing mechanochromic or intensity modulation effects. The second part describes the soft optomechanical systems for the development of light induced mechanical actuators based on different actuation mechanisms, such as photothermal effects and phase transitions, among others. The final section provides a critical analysis of the main limitations of current soft optomechanical systems and the progress that is required for future devices.

Enhanced second-order nonlinearity and tunable plasmon induced transparency in noncoplanar Dirac semimetal system

Plasmon Induced Transparency (PIT) effect possesses the characteristics of sharp and pronounced spectral response and considerable group delay. In this work, a PIT system consists of two noncoplanar Dirac semimetal particles (DSPs) has been studied by finite-difference time-domain (FDTD) method. Tailoring of this PIT system can be achieved by structural parameters, Fermi energy (EF), refractive index (RI) of dielectric medium and polarization angle of incident light. Benefitted from its smaller particle size, the bandwidth of PIT window in this DSPs system is up to 3.94 THz, which is much broader than in bulk Dirac semimetal PIT system (about 0.36 THz). An efficient second order nonlinearity of this DSPs system is obtained for its intensive localized field, non-centrosymmetric structureunique and unique electromagnetic mode. The second-order nonlinear conversion efficiency in this system is up to 10−6 to 10−5 for its noncoplanar structure. This noncoplanar DSPs system can also achieve approximate linear light intensity modulation effect of its second harmonic waves (SHWs). This developed noncoplanar DSPs structure could provide guidance for the design of high integration Dirac semimetal THz devices.

Polarization-dependent dissipative soliton intensity modulation enabled repetition-rate-switchable CPA system

We report a watt-level, repetition-rate-switchable all-fiber chirped pulse amplification (CPA) system by using polarization-dependent dissipative soliton intensity modulation effect. The intensity modulation for pulse repetition rate tuning is realized by combination of the polarization discrimination device (i.e., polarizer) and the polarization-rotating vector soliton (PRVS). Up to ~100% intensity modulation depth with a period of two cavity roundtrips for the PRVS seed was obtained by adjusting the dissipative soliton polarization state that was injected into the polarizer. Relying on this mechanism, the repetition rate of the output pulse from the CPA system can be dynamically switched between 1.37 MHz and 2.74 MHz. The pulse energy of ~2.0 μJ and ~2.2 μJ were achieved for the repetition rates of 1.37 MHz and 2.74 MHz, corresponding to 1.12 ps and 970 fs pulse duration, respectively. These findings would provide an alternative method for dynamic tuning of pulse repetition rate in high power laser systems, which also underpins the significance of fundamental research of vector dissipative solitons in practical applications such as flexible high-energy pulse laser systems.

Interference of Counterpropagating Waves in a “Graphene–Dielectric” Planar Lamellar Structure

The incidence of two coherent waves traveling in opposite directions on opposite surfaces of a planar layered-periodic graphene–dielectric structure has been investigated. It has been shown in the long-wave approximation that it is possible to control the intensity of the outgoing waves and absorption of radiation in the structure by changing the phase difference of the waves that are incident on the structure. There are close to optimal conditions for the intensity modulation effect in the terahertz frequency domain and modulation of the absorption capacity of the structure is possible in the near infrared and visible ranges.

Интерференция встречных волн в планарной мелкослоистой структуре графен--диэлектрик"

The incidence of two counterpropagating coherent waves on the opposite surfaces of a planar periodically layered graphene – dielectric structure was studied. In the long-wave approximation, it is shown that, due to the variation of the phase difference of waves incident on the structure, it is possible to control the intensity of outgoing waves and the absorption of radiation in the structure. In the terahertz frequency domain there are close to optimal conditions for the realization of the intensity modulation effect, and in the near-IR and visible ranges the modulation of the absorbance of the structure is possible.

Quantitative correlation between facets defects of RDX crystals and their laser sensitivity

In this work, the {210} facets of cyclotrimethylenetrinitramine (RDX) single crystals with different quality were studied by scanning electron microscopy and atomic force microscopy. Their laser sensitivity was then assessed using a direct laser ignition test irradiated with ultraviolet laser (wavelength: 355nm, pulse width: 6.4ns). Quantitative relationships between laser sensitivity and surface defects of RDX (210) and (2¯1¯0) facets were investigated. It is determined that the laser sensitivity exhibits significant correlation with the surface roughness, size of which is comparable with scales of laser wavelength. 3D FDTD simulations disclose that this relationship can be well explained with light intensity modulation effects induced by micro-defects on the initial plane wave.

In-plane anisotropic photoresponse in all-polymer planar microcavities

We report on the optical photomodulation properties of all-polymer planar microcavities in which the photochromic poly((4-pentyloxy-3’-methyl-4’-(6-methacryloxyhexyloxy))azobenzene) (PMA4) acts as photoresponsive cavity layer. We induce the trans-cis isomerization process of the azobenzene group by polarized 405 nm CW-laser irradiation, while the backward process is driven by unpolarized CW-laser irradiation at 442 nm. The all-optical photoisomerization process induces a remarkable in-plane anisotropic spectral shift of the cavity modes for the first and second order photonic band gaps. The spectral and intensity modulation effects for these flexible all-polymer microcavities are discussed with respect to those so far reported in literature for analogous systems.

Commissioning of intensity modulated neutron radiotherapy (IMNRT)

Intensity modulated neutron radiotherapy (IMNRT) has been developed using inhouse treatment planning and delivery systems at the Karmanos Cancer Center∕Wayne State University Fast Neutron Therapy facility. The process of commissioning IMNRT for clinical use is presented here. Results of commissioning tests are provided including validation measurements using representative patient plans as well as those from the TG-119 test suite. IMNRT plans were created using the Varian Eclipse optimization algorithm and an inhouse planning system for calculation of neutron dose distributions. Tissue equivalent ionization chambers and an ionization chamber array were used for point dose and planar dose distribution comparisons with calculated values. Validation plans were delivered to water and virtual water phantoms using TG-119 measurement points and evaluation techniques. Photon and neutron doses were evaluated both inside and outside the target volume for a typical IMNRT plan to determine effects of intensity modulation on the photon dose component. Monitor unit linearity and effects of beam current and gantry angle on output were investigated, and an independent validation of neutron dosimetry was obtained. While IMNRT plan quality is superior to conventional fast neutron therapy plans for clinical sites such as prostate and head and neck, it is inferior to photon IMRT for most TG-119 planning goals, particularly for complex cases. This results significantly from current limitations on the number of segments. Measured and calculated doses for 11 representative plans (six prostate∕five head and neck) agreed to within -0.8 ± 1.4% and 5.0 ± 6.0% within and outside the target, respectively. Nearly all (22∕24) ion chamber point measurements in the two phantom arrangements were within the respective confidence intervals for the quantity [(measured-planned)∕prescription dose] derived in TG-119. Mean differences for all measurements were 0.5% (max = 7.0%) and 1.4% (max = 4.1%) in water and virtual water, respectively. The mean gamma pass rate for all cases was 92.8% (min = 88.6%). These pass rates are lower than typically achieved with photon IMRT, warranting development of a planar dosimetry system designed specifically for IMNRT and∕or the improvement of neutron beam modeling in the penumbral region. The fractional photon dose component did not change significantly in a typical IMNRT plan versus a conventional fast neutron therapy plan, and IMNRT delivery is not expected to significantly alter the RBE. All other commissioning results were considered satisfactory for clinical implementation of IMNRT, including the external neutron dose validation, which agreed with the predicted neutron dose to within 1%. IMNRT has been successfully commissioned for clinical use. While current plan quality is inferior to photon IMRT, it is superior to conventional fast neutron therapy. Ion chamber validation results for IMNRT commissioning are also comparable to those typically achieved with photon IMRT. Gamma pass rates for planar dose distributions are lower than typically observed for photon IMRT but may be improved with improved planar dosimetry equipment and beam modeling techniques. In the meantime, patient-specific quality assurance measurements should rely more heavily on point dose measurements with tissue equivalent ionization chambers. No significant technical impediments are anticipated in the clinical implementation of IMNRT as described here.

Effects of Intensity Modulation of Light Source on Brillouin Optical Correlation Domain Analysis

The effects of the intensity modulation (IM) of light source on fiber-distributed sensors based on Brillouin optical correlation domain analysis (BOCDA) are analyzed by numerical simulation, and the results are experimentally confirmed. We show that the shape of the Brillouin gain spectrum in the BOCDA system has a particular dependence on the optical spectrum of light source and that it can be controlled and tailored by proper modification of the optical spectrum using an additional IM. In the experiments, we applied several IM waveforms based on the simulation results for confirmation. Additionally, a distributed strain measurement along a 1-km optical fiber with a 30-cm spatial resolution is demonstrated by applying a proper IM scheme, which is the longest range reported using the BOCDA system

Effect of Intensity Modulation on Measuring of FM Index

This paper derives an exact expression to compute the magnitude of the optical line spectrum when DFB laser is directly modulated by sinusoidal signal. Measuring technique using scanning Fabry-Perot interferometer (FPI) to compute the frequency modulation (FM) index of the laser diode (LD) have been reported in earlier literature. The accuracy of this technique will be revised in this paper theoretically.

High-energy angle-resolved photoemission of NaMo6O17

Abstract Angle-resolved photoelectron spectroscopy of quasi-two-dimensional NaMo6O17 has been investigated with photon energies greater than 70 eV. The underlying quasi-one-dimensional band structure is visualized in multiple Brillouin zones by the constant binding-energy intensity mapping technique. Brillouin zone intensity modulation effects are observed in Fermi-edge intensity maps both as a function of k|| (angle) and of kz (photon energy). Experimental challenges arising from small sample sizes, detection geometry and susceptibility to beam-induced surface damage are also discussed.

The effect of reflections on the system performance of intensity modulated laser diodes

The performance degradation incurred by unwanted external reflections in high-speed digital optical communication systems using intensity-modulated single-longitudinal-mode laser diodes is investigated by numerical simulation of the rate equations. The effects of intensity modulation on the chaotic behavior in the laser output are examined and performance estimates for 0.5, 2.5, and 5 Gb/s systems are made. For example, it is found that to incur less than 0.25-dB power penalty in a 2.5-Gb/s system using a positive-intrinsic-negative photodetector, the reflected light in the laser pigtail should be at least 36 dB below that of the transmitted light.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Power spectrum of directly modulated single-mode semiconductor lasers: Chirp-induced fine structure

The time-averaged power spectrum of a single-mode semiconductor laser under direct current modulation is calculated using the small-signal analysis of the stochastic rate equations. The general formalism includes the effect of frequency chirping owing to current modulation as well as the effect of phase diffusion related to spontaneous emission. Chirp-induced dynamic line broadening is shown to result from a superposition of the additional unresolved sidebands generated at multiples of the modulation frequency on both sides of the optical line. The effect of intensity modulation is to introduce an asymmetry such that the low-frequency sideband has a relatively higher amplitude. The theory explains reasonably well the reported experimental observations. At the same time it provides physical insight into the dynamic process of frequency chirping and its relation to the frequency modulation. In particular, the frequency and the decay rate of transient relaxation oscillations govern the interplay between simultaneously occurring intensity and frequency modulations.

Effect of intensity modulation on radiation-induced melting and vaporization of solids

Linear response of steady-state melting and of evaporation processes to the modulation of radiation intensity is considered in the framework of a Stephan-like approach. It is shown that resonance behaviour of the surface temperature pertinent to the evaporation process persists in the case where the evaporation front is preceded by a melting transition.