Gaussian Pulse Width Research Articles

Improving the electrostatic design of the Jefferson Lab 300 kV DC photogun.

The 300kV DC high voltage photogun at Jefferson Lab was redesigned to deliver electron beams with a much higher bunch charge and improved beam properties. The original design provided only a modest longitudinal electric field (Ez) at the photocathode, which limited the achievable extracted bunch charge. To reach the bunch charge goal of approximately few nC with 75ps full-width at half-maximum Gaussian laser pulse width, the existing DC high voltage photogun electrodes and anode-cathode gap were modified to increase Ez at the photocathode. In addition, the anode aperture was spatially shifted with respect to the beamline longitudinal axis to minimize the beam deflection introduced by the non-symmetric nature of the inverted insulator photogun design. We present the electrostatic design of the original photogun and the modified photogun and beam dynamics simulations that predict vastly improved performance. We also quantify the impact of the photocathode recess on beam quality, where recess describes the actual location of the photocathode inside the photogun cathode electrode relative to the intended location. A photocathode unintentionally recessed/misplaced by sub-millimeter distance can significantly impact the downstream beam size.

Tunable Nanoporous Anodic Alumina Photonic Crystals by Gaussian Pulse Anodization.

This study presents a Gaussian pulse anodization approach to generate nanoporous photonic crystals with highly tunable and controllable optical properties across the visible-NIR spectrum. Nanoporous anodic alumina Gaussian photonic crystals (NAA-GPCs) are fabricated in oxalic acid electrolyte by Gaussian pulse anodization, a novel form of pulse-like anodization. The effect of the Gaussian pulse width in the anodization profile on the optical properties of these photonic crystals is assessed by systematically varying this fabrication parameter from 5 to 60 s. The optical features of the characteristic photonic stopband (PSB) of NAA-GPCs-the position of the central wavelength, full width at half-maximum, and intensity-are found to be highly dependent on the Gaussian pulse width, the angle of incidence of incoming photons, and the nanopore diameter of NAA-GPCs. The effective medium of NAA-GPCs is assessed by monitoring spectral shifts in their characteristic PSB upon infiltration of their nanoporous structure with analytical solutions of d-glucose of varying concentration (0.0125-1 M). Experimental results are validated and mechanistically described by theoretical simulations, using the Looyenga-Landau-Lifshitz effective medium approximation model. Our findings demonstrate that Gaussian pulse anodization is an effective nanofabrication approach to producing highly sensitive NAA-based PC structures with versatile and tunable PSBs across the spectral regions. The findings provide new exiting opportunities to integrate these unique PC structures into photonic sensors and other platform materials for light-based technologies.

Picosecond kilohertz-class cryogenically cooled multistage Yb-doped chirped pulse amplifier.

A multistage cryogenic chirped pulse amplifier has been developed, utilizing two different Yb-doped gain materials in subsequent amplifier stages. A Yb:GSAG regenerative amplifier followed by a Yb:YAG power amplifier is able to deliver pulses with a broader bandwidth than a system using only one of these two gain media throughout. We demonstrate 90 mJ of pulse energy (113 W of average power) uncompressed and 67 mJ (84 W of average power) compressed at 1.25 kHz pulse repetition frequency, 3.0 ps FWHM Gaussian pulse width, and near-diffraction-limited (M2<1.3) beam quality.

Wideband and low-dispersion engineered slow light using liquid infiltration of a modified photonic crystal waveguide.

We present a wideband and low-dispersion slow-light photonic crystal waveguide with a large normalized delay-bandwidth product that can be exploited in many ultra-compact all-optical devices, such as modulators and switches. The proposed new approach is based on infiltrating optical fluid into the first and second rows of the shifted air holes adjacent to the line-defect waveguide in a hexagonal lattice of photonic crystal. The simulation results show that the normalized delay-bandwidth product can be enhanced to a large value of 0.469 with a wide bandwidth operation of 36.8nm in the C-band frequency optical communication window. Furthermore, by means of two-dimensional finite-difference time-domain calculations, the low-dispersion slow-light propagation is demonstrated by simulating the temporal Gaussian pulse width broadening.

Enhanced sheath heating in capacitively coupled discharges due to non-sinusoidal voltage waveforms

Through the use of particle-in-cell simulations, we demonstrate that the power deposition in capacitively coupled discharges (in argon) can be increased by replacing sinusoidal waveforms with Gaussian-shaped voltage pulses (with a repetition frequency of 13.56 MHz). By changing the Gaussian pulse width, electron heating can be directly controlled, allowing for an increased plasma density and ion flux for the same gas pressure and geometrical operating conditions. Analysis of the power deposition profiles and electron distribution functions shows that enhanced electron-sheath heating is responsible for the increased power absorption.

Nano-Power Wireless Wake-Up Receiver With Serial Peripheral Interface

We designed, implemented, tested and measured an ultra low power Wake Up Receiver (WUR), intended for use in Wireless Body Area Networks (WBAN). Gaussian On-Off Keying (GOOK) and Pulse Width Modulation (PWM) are used to modulate and encode, respectively, the preamble signal. The receiver incorporates a decoder to enable Serial Peripheral Interface (SPI). WUR was also comprehensively tested for power consumption and robustness to RF interference from wireless devices commonly found in the vicinity of persons utilising WBAN technology. Our results and comparative evaluation demonstrate that the achieved listening power of 270nW for the Wake Up Receiver is significantly lower power consumption than for the other state-of-the-art. The proposed preamble detection scheme can significantly reduce false wake ups due to other wireless devices in a WBAN. Additionally, SPI significantly reduces the overall power consumption for packet reception and decoding.

Optimal input Gaussian pulse width for transmission in dispersive nonlinear fibers

Using the variational method, we derive simple, closed-form algebraic expressions that approximate the optimal input rms pulse width and the corresponding minimum output rms width for Gaussian pulses subject to both dispersive and nonlinear effects in single-mode fibers. We present results in both numerical and analytical forms and confirm them by the split-step Fourier numerical method. Our results cover both normal and anomalous dispersion in fibers with gain and loss. For the case of normal dispersion we show that both the optimal input and output widths are asymptotically linearly dependent on distance and dependent on the square roots of the dispersion coefficient and the transmitted power.

The influence of molecular rotational diffusion on Gaussian pulse-induced third-order electric polarisation in liquids

Time evolution curves of the changes in nonlinear electric polarisation induced by Gaussian pulses are calculated theoretically with the Smoluchowski-Debye molecular rotational diffusion equation not including the influence of the moment of inertia of the molecules or their interactions. Graphs show the dynamics of the third-order electric polarisation versus the Gaussian pulse width and the parameter R, defining the balance between the dipolar and anisotropically polarisable properties of the molecules.

The Dynamics of Populating The Lowest Triplet State Of Benzophenone Following Singlet Excitation

Measurements of the build-up of triplet-triplet absorption at 5300 A have been made during and subsequent to the excitation of benzophenone by 5 psec pulses of 3545 A radiation (frequency tripled Nd 3+: glass fundamental). The data were fitted to a simple model that included the finite gaussian pulse width and results for the assumed process S i ▪T 1 are: K −1=16.5±3 psec for benzophenone in ethanol; k −1 = 30 ±5 psec for benzophenone in benzene. This new type of solvent effect on triplet build-up is discussed.

Pulse Transmission Through a Dielectric Optical Waveguide

Waveguide propagation of a pulse-modulated carrier wave is formulated to include distortion due to dispersion in both attentuation and phase velocity. An optimum input gaussian pulse width exists for maximum information carrying capacity. Results are applied to a numerical study of several singlemode glass optical waveguides in which mode and dielectric dispersion may total zero at some wavelength. For our low-loss (20 dB/km) guides in kilometer lengths, information rates of at least 3 x 10(10) bits/sec should be attainable.