Wavelength-dependent Modulation Research Articles

纳米金膜及金壳表面局域等离激元对上转换荧光波长的选择调控

纳米金膜及金壳表面局域等离激元对上转换荧光波长的选择调控

Wavelength-Dependent Three-Dimensional Volumetric Optical Vortices Modulation Based on Metasurface

The emergence of the metasurface has spawned an ultrathin, compact, and planner way to generate the orbital angular momentum (OAM) beam array. Several types of OAM beam array generators based on the metasurface have been reported, however, most of them only performed at the certain wavelength for lack of the wavelength-dependent modulation, which restricted the flexibility and capacity of the generators. Here, we propose a single-layered metasurface to realize the generation of the wavelength-dependent three-dimensional (3-D) volumetric vortex beam array. The metasurface is composed by two different nanoantennas, which shows the distinct properties of wavelength selectivity and wavelength-dependent phase modulation. By employing such properties, 3-D volumetric vortex beams operating at different wavelengths can be multiplexed. Our design may facilitate the development of the optical multiplexing, and the wavelength-dependent control of the OAM light will improve the capacity and the security of the optical information.

Design trade-off and proof of concept for LOUPE, the Lunar Observatory for Unresolved Polarimetry of Earth.

We provide a proof of the technical feasibility of LOUPE, the first integral-field snapshot spectropolarimeter, designed to monitor the reflected flux and polarization spectrum of Earth. These are to be used as benchmark data for the retrieval of biomarkers and atmospheric and surface characteristics from future direct observations of exoplanets. We perform a design trade-off for an implementation in which LOUPE performs snapshot integral-field spectropolarimetry at visible wavelengths. We used off-the-shelf optics to construct a polarization modulator, in which polarization information is encoded into the spectrum as a wavelength-dependent modulation, while spatial resolution is maintained using a micro-lens array. The performance of this design concept is validated in a laboratory setup. Our proof-of-concept is capable of measuring a grid of 50 × 50 polarization spectra between 610 and 780 nm of a mock target planet - proving the merit of this design. The measurements are affected by systematic noise on the percent level, and we discuss how to mitigate this in future iterations. We conclude that LOUPE can be small and robust while meeting the science goals of this particular space application, and note the many potential applications that may benefit from our concept for doing snapshot integral-field spectropolarimetry.

Design and application of photo-reversible elastomer networks by using the [4πs+4πs] cycloaddition reaction of pendant anthracene groups

Abstract In this work, the photo-reversible [4πs+4πs] cycloaddition reaction of anthracene moieties is employed to impart wavelength dependent properties into carboxylated nitrile butadiene rubber networks. Crosslinking of the side chain functionalized rubber is achieved by UV induced dimerization of pendant anthracene groups at wavelengths above 300 nm whilst a subsequent deep UV exposure (λ = 254 nm) results in a well-defined cleavage of the crosslinks. Crosslink kinetics and photo-reversibility of the dimerization reaction are determined by spectroscopic measurements. The changes in network structure and chain dynamics over multiple crosslinking and cleavage cycles are studied in detail by low field NMR. In thin films, the wavelength dependent changes in solubility are employed for the preparation of reversible photoresists enabling the preparation of 2D microstructures and a switching between negative- and positive-type patterns. Along with thin films, the wavelength dependent modulation of thermo-mechanical properties is also demonstrated for macroscopic samples, which shows the versatility of these optically stimuli-responsive networks.

Source-Manipulating Wavelength-Dependent Continuous-Variable Quantum Key Distribution with Heterodyne Detectors

The intensities of signal and local oscillator (LO) can be elegantly manipulated for the noise-based quantum system while manipulating the wavelength-dependent modulation in source to increase the performance of the continuous-variable key distribution in terms of the secret key rate and maximal transmission distance. The source-based additional noises can be tuned and stabilized to the suitable values to eliminate the effect of the LO fluctuations and defeat the potential attacks in imperfect quantum channels. It is firmly proved that the secret key rate can be manipulated in source over imperfect channels by the intensities of signal and LO with different wavelengths, which have an effect on the optimal signal-to-noise ratio of the heterodyne detectors resulting from the detection efficiency and the additional electronic noise as well. Simulation results show that there is a nice balance between the secret key rate and the maximum transmission distance.

Calibration-free scanned wavelength modulation spectroscopy--application to H(2)O and temperature sensing in flames.

A calibration-free scanned wavelength modulation spectroscopy scheme requiring minimal laser characterization is presented. Species concentration and temperature are retrieved simultaneously from a single fit to a group of 2f/1f-WMS lineshapes acquired in one laser scan. The fitting algorithm includes a novel method to obtain the phase shift between laser intensity and wavelength modulation, and allows for a wavelength-dependent modulation amplitude. The scheme is demonstrated by detection of H(2)O concentration and temperature in atmospheric, premixed CH(4)/air flat flames using a sensor operating near 1.4 µm. The detection sensitivity for H(2)O at 2000 K was 4 × 10(-5) cm(-1) Hz(-1/2), and temperature was determined with a precision of 10 K and absolute accuracy of ~50 K. A parametric study of the dependence of H(2)O and temperature on distance to the burner and total fuel mass flow rate shows good agreement with 1D simulations.

Thermo-optic control of dielectric-loaded plasmonic Mach–Zehnder interferometers and directional coupler switches

We report detailed experimental studies of compact fiber-coupled dielectric-loaded plasmonic waveguide components—Mach–Zehnder interferometers (MZIs) and directional couplers (DCs)—whose operation at telecom wavelengths is controlled via the thermo-optic effect by electrically heating the gold stripe of dielectric-loaded plasmonic waveguides. The effect of the gaps isolating the heated part of the waveguide from the rest of the structure was examined showing the presence of a Fabry–Pérot cavity in this MZI arm. Wavelength-dependent modulation is demonstrated with MZI-based components, and wavelength dependent low power (∼0.92 mW) rerouting is achieved with DC switches. Furthermore, simulations were performed to confirm the switching characteristics of the components.

Fourier-transform photocurrent spectroscopy using a supercontinuum light source

We demonstrate an implementation of frequency-encoded photocurrent spectroscopy using a super-continuum light source. The spectrally broad light is spatially dispersed and modulated with a special mechanical chopper design that permits a continuous wavelength-dependent modulation. After recombination, the light beam contains a frequency encoded spectrum which enables us to map the spectral response of a given sample in 60 ms and with a lateral resolution of 10 μm.

Wavelength-Dependent Modulation of Brain Responses to a Working Memory Task by Daytime Light Exposure

In addition to classical visual effects, light elicits nonvisual brain responses, which profoundly influence physiology and behavior. These effects are mediated in part by melanopsin-expressing light-sensitive ganglion cells that, in contrast to the classical photopic system that is maximally sensitive to green light (550 nm), is very sensitive to blue light (470-480 nm). At present, there is no evidence that blue light exposure is effective in modulating nonvisual brain activity related to complex cognitive tasks. Using functional magnetic resonance imaging, we show that, while participants perform an auditory working memory task, a short (18 min) daytime exposure to blue (470 nm) or green (550 nm) monochromatic light (3 x 10(13) photons/cm2/s) differentially modulates regional brain responses. Blue light typically enhanced brain responses or at least prevented the decline otherwise observed following green light exposure in frontal and parietal cortices implicated in working memory, and in the thalamus involved in the modulation of cognition by arousal. Our results imply that monochromatic light can affect cognitive functions almost instantaneously and suggest that these effects are mediated by a melanopsin-based photoreceptor system.

Diffusion of nitroglycerin from drug delivery patches through micro-fibre filters using Fourier transform infrared photoacoustic spectrometry

In this paper, the diffusion of the angina therapeutic agent, nitroglycerin through a skin mimetic is described. The mimetic is a poly(ethylene) glycol loaded microfibre filter to which a transdermal drug patch is attached. The diffusion process is monitored using dynamic scanning Fourier transform infrared (FTIR)-photoacoustic spectrometry in which the IR beam illuminates the filter with the transdermal patch on the underside. Thus, the nitroglycerin diffuses up through the filter. Using different thermal diffusion lengths, as determined by the wavelength dependent modulation frequency of the FTIR spectrometer, the diffusion process is monitored. A convenient model is developed to provide a direct measurement of the diffusion coefficient of nitroglycerin through the poly(ethylene) glycol loaded filter.

A 4-GHz frequency-domain fluorometer with internal microchannel plate photomultiplier cross-correlation

We have developed and tested a multifrequency phase/modulation fluorometer based on the Hamamatsu Model R2024U gatable microchannel plate photomultiplier (MCP-PMT), using internal MCP-PMT cross-correlation. This internal mixing is accomplished by biasing and modulating the gating mesh which is located 0.2 mm behind the photocathode. Near the photocathode center, no high-frequency photocurrent modulation was achieved. Within a circular area near the photocathode edge, however, the R2024U allows accurate phase shift and demodulation measurements up to at least 4.5 GHz, the frequency limit of our PMT-modulation amplifier. By mixing immediately after the photocathode, there is no decrease in the time resolution due to transit time spread, and the MCP has to process only low-frequency signals. This means no low-level high-frequency signal voltages have to be handled in this fluorometer, and the problems of RF shielding become much less critical. Also, the effective output impedance of the PMT has been increased, resulting in a 43-dB increase in the PMT output signal power. In principle, more MCPs could be built into the PMT, allowing an improved fluorescence detection limit. We have used the method of reference fluorophores in order to compensate for pronounced PMT color effects, a wavelength-dependent modulation, and a wavelength-dependent time shift. No color correction is required in the case of time-dependent depolarization. The performance of the instrument was verified by measurements of the intensity decay of perylene, which showed a single-exponential decay, and by measurements of the decay of tryptophan in water, which showed a double-exponential decay, as expected. Additionally, we measured a 231-ps decay time for rose bengal in a methanol:water mixture (50:50), and a 183-ps correlation time. This method of detection and mixing could be of particular usefulness in studies of time-dependent photon migration in tissues, which require high modulation frequencies, but do not require the detector to be free of color effects.