Sufficient Laser Power Research Articles

Columnar excitation fluorescence microscope for accurate evaluation of quantum properties of color centers in bulk materials

Color centers in wide band-gap semiconductors, which have superior quantum properties even at room temperature and atmospheric pressure, have been actively applied to quantum sensing devices. Characterizing the quantum properties of the color centers in the semiconductor materials and ensuring that these properties are uniform over a wide area are key issues for developing quantum sensing devices based on color centers. In this article, we have developed an optics design protocol optimized for evaluating the quantum properties of color centers and have used this design approach to develop a new microscopy system called columnar excitation fluorescence microscope (CEFM). The essence of this system is to maximize the amount of fluorescence detection of polarized color centers, which is achieved by large-volume and uniform laser excitation along the sample thickness with sufficient laser power density. This laser excitation technique prevents undesirable transitions to undesirable charge states and undesirable light, such as unpolarized color center fluorescence, while significantly increasing the color center fluorescence. This feature enables fast measurements with a high signal-to-noise ratio, making it possible to evaluate the spatial distribution of quantum properties across an entire mm-size sample without using a darkroom, which is difficult with typical confocal microscope systems.

Enhanced plasticity in laser additive manufactured Nb-reinforced bulk metallic glass composite

The microstructures and mechanical properties of 50 wt% Nb-reinforced Zr-based bulk metallic glass composites, (BMGCs), manufactured via laser directed energy deposition (LDED) with two different laser powers, P , are investigated and compared with those of LDED manufactured monolithic bulk metallic glass (BMG). Results show that both BMGCs have a multi-component microstructure that includes dual-sized Nb particles and devitrification-induced nano crystals at the melt-pool boundaries whereas the monolithic BMG contains only the latter. The nanocrystals at the melt-pool boundaries embrittle the LDED manufactured monolithic BMG, which reflects as a higher yield strength but negligible plastic deformation in uniaxial compression. In contrast, both BMGCs undergo significant plastic deformation as the Nb-reinforcements, besides improving plasticity by arresting propagating shear bands, reduces the enthalpy of relaxation, Δ H rel , of the matrix and decreases the volume fraction of the nanocrystallites, V nc , at the melt-pool boundaries. However, amongst the two, the BMGC manufactured at higher P exhibits much higher shear band plasticity, despite having higher V nc and lower Δ H rel . This is rationalized by analyzing the load transfer characteristics of the Nb-BMG matrix interfaces in the two BMGCs. • LDED manufactured Nb-reinforced Zr-based BMGCs have significantly improved plasticity. • Nb induced plasticity improvement is achieved through limiting the structural relaxation of amorphous matrix. • Higher thermal diffusivity of Nb can minimize the devitrification induced brittle phases and thus enhance plasticity. • Partially dissolving Nb in the amorphous matrix by sufficient laser power can maximize shear band arresting capabilities.

Relativistic Light Sails Need to Billow.

We argue that light sails with nanometer-scale thicknesses that are rapidly accelerated to relativistic velocities by lasers must be significantly curved in order to reduce their intrafilm mechanical stresses and avoid tears. Using an integrated opto-thermo-mechanical model, we show that the diameter and radius of curvature of a circular light sail should be comparable in magnitude, both on the order of a few meters, in optimal designs for gram-scale payloads. Moreover, we demonstrate that, when sufficient laser power is available, a sail's acceleration length decreases as its curvature increases. Our findings provide critical guidance for emerging light sail design programs, which herald a new era of interstellar space exploration to destinations such as the Oort cloud, the Alpha Centauri system, and beyond.

Control of relative electron densities and spacing of two laser induced plasmas by spatial light modulation of femtosecond laser

This study demonstrates a novel technique for independently controlling the relative electron densities and axial separation of two laser induced plasmas (LIPs) formed in air by an ultrashort pulse laser (USPL). A spatial light modulator (SLM) provides the means of control by altering the wavefront of a 35 fs, 1.6–2.5 mJ pulse from a Ti:Sapphire USPL with a 790 nm center wavelength. After modification by the SLM, a lens focuses the pulse, which increases its intensity and generates plasma by ionizing air. Holograms displayed on the SLM diffract a controlled amount of laser energy to a first-order focal spot some distance from the lens focus, and sufficient laser power generates two LIPs spaced from one another along the laser propagation direction. The hologram contrast dictates the relative intensity of the light arriving at each focus, and the spatial gradient of the phase shift applied by the hologram determines the distance between the two foci. Analytic solutions of linear light propagation and scalar diffraction theory computed with the convolution method are used to determine initial hologram designs meant to deliver various foci spacings and relative intensities. Ultrashort pulse lasers (USPLs) supply pulse powers sufficient to induce filamentation in air, a result of non-linear optical phenomena that extends the range of intense laser propagation and generates plasma. Comparing images of linear propagation at low laser powers with relative line-integrated electron density measurements taken during plasma formation indicate any extant non-linear processes do not prevent predictable control of plasma geometry for 0.3 m and 0.5 m focal lengths.

Comparing the fundamental imaging depth limit of two-photon, three-photon, and non-degenerate two-photon microscopy.

We have systematically characterized the degradation of imaging quality with depth in deep brain multi-photon microscopy, utilizing our recently developed numerical model that computes wave propagation in scattering media. The signal-to-background ratio (SBR) and the resolution determined by the width of the point spread function are obtained as functions of depth. We compare the imaging quality of two-photon (2PM), three-photon (3PM), and non-degenerate two-photon microscopy (ND-2PM) for mouse brain imaging. We show that the imaging depth of 2PM and ND-2PM are fundamentally limited by the SBR, while the SBR remains approximately invariant with imaging depth for 3PM. Instead, the imaging depth of 3PM is limited by the degradation of the resolution, if there is sufficient laser power to maintain the signal level at large depth. The roles of the concentration of dye molecules, the numerical aperture of the input light, the anisotropy factor g, noise level, input laser power, and the effect of temporal broadening are also discussed.

Laser-driven calorimetry measurements of petroleum and biodiesel fuels

Thermochemical characteristics were determined for several National Institute of Standards and Technology standard-reference-material petroleum and biodiesel fuels, using a novel laser-heating calorimetry technique. Measurements focused on the sample thermal behavior, specific heat release rate, and total specific heat release. The experimental apparatus consists of a copper sphere-shaped reactor mounted within a chamber, along with laser-beam-steering optical components, gas-supply manifold, and a computer-controlled data-acquisition system. At the center of the reactor, liquid sample is injected onto a copper pan substrate that rests and is in contact with a fine-wire thermocouple. A second thermocouple is in contact with the inner reactor sphere surface. The reactor is heated from opposing sides by a continuous-wave, near-infrared laser beam to achieve nearly uniform sample temperature. The change in temperature with time (thermogram) is recorded for both thermocouples, and compared to a baseline thermogram (without liquid in the pan). The thermograms are then processed (using an equation for thermal energy conservation) for the thermochemical information of interest. The results indicated that the energy reaching the pan is dominated by radiative heat transfer processes, while the dominant thermal process for the reactor sphere is the stored (internal) thermal energy within the sphere material. Sufficient laser power is necessary to detect the fuel thermal-related characteristics, and the required power can differ from one fuel to another. With sufficient laser power, one can detect the preferential vaporization of the lighter and heavier fuel fractions. The total specific heat release obtained for the different conventional and biodiesel fuels used in this investigation were similar to the expected values available in the literature.

Current pulse shaping of the load current on PTS

The typical rise time of PTS machine is ∼110 ns with about 10 MA peak current under short pulse mode when all 24 modules discharge simultaneously. By distributing the trigger times of 12 laser beams logically and adjusting the statues of the pulse output switches, longer rise-time pulse can be obtained on the PTS facility. Based on the required pulse shape, whole circuit simulations will be used to calculate the trigger times of each laser triggering gas switch and the status of the pulse output switches. The rise time of the current is determined by the time difference between the first and last trigged laser triggering gas switches. In order to trigger the laser triggering gas switch, sufficient laser power is needed to be sent into the gap of the gas switches. The gas pressure and voltage difference on the two electrodes of the gas switches also affect the triggering of the gas switches, and the voltage added on the gas switch is determined by its transition time. Traditionally the trigger time difference should be less than the transition time of the two neighboring modules. A new simulation model of PTS shows one can break this transition time limits. Series of current pulse shaping experiments have been investigated on the PTS (Primary Test Stand). As results, more than 5 MA peak current were successfully achieved on the load with a rise time of 600 ns. This study and experiments of the pulse shaping on PTS demonstrate the adaptable ability of the PTS for offering different waveform of mega ampere current pulse for different research purpose.

Continuous-wave cavity ring-down technique for accurate measurement of high reflectivity

A continuous-wave cavity ring-down (CW-CRD) technique employing a broadband diode laser is developed for high reflectivity measurement. The theory of square-wave modulated CW-CRD is presented. The spectrum of the broadband CW diode laser covers numerous free spectral ranges (FSRs) so that sufficient laser power is coupled into the cavity. Both amplitude and phase-shift of the first harmonic of the CRD signal, measured at an appropriate frequency range, are detected by a lock-in method and fitted to obtain the ring-down time and reflectivity. The measurements are repeated with five different cavity lengths and all the fitted reflectivities are in excellent agreement, indicating a high reliability of the CW-CRD technique. The reflectivity of the cavity mirror is determined statistically to be 99.70%, with an uncertainty of 0.01%.

High-Quality Flat-Top Micromachining of Silica by a CW CO$_{2}$ Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This letter demonstrates a simple and fast technique that dramatically improves the micromachined surface quality of silica substrates processed by a continuous-wave CO<emphasis><formula formulatype="inline"><tex>$_{2}$</tex> </formula></emphasis> laser. When sufficient laser power is directed at the surface of a sample, its temperature increases beyond the boiling point. Melted material is ejected and a groove is created. Some of the ablated material redeposits on each side of the groove, altering the surface quality of the substrate. To circumvent this problem, we deposit a polymer overlay as a sacrificial film which protects the surface during the ablation process, resulting in a flat surface on either side of the groove at very high writing speeds. The grooves can be used as an aid to passive alignment for an optical fiber, as diffractive optical elements or to create high-quality microfluidic chips. </para>

Fast switching of alkali atom dispensers using laser-induced heating

We show that by using an intense laser source to locally heat an alkali atom dispenser, one can generate a high flux of atoms followed by fast recovery (&amp;lt;100ms) of the background pressure when the laser is extinguished. For repeated heating pulses a switch-on time for the atomic flux of 200ms is readily attainable. This technique is suited to ultracold atom experiments using simple ultrahigh vacuum (UHV) chambers. Laser-induced heating provides a fast repetition of the experimental cycle, which, combined with low atom loss due to background gas collisions, is particularly useful for experiments involving far-off resonance optical traps, where sufficient laser power (0.5–4W) is readily available.

Eclipse laser photodetachment method for avoiding probe surface ablation in negative ion measurement

Direct laser irradiation to an electrostatic probe disturbs the negative ion signals of laser photodetachment (LPD) in helium–hydrogen plasmas, particularly when the electron density is considerably high. In order to analyse the characteristics and production mechanism of ablation signals, laser irradiation experiments were performed on a tungsten surface using helium plasmas. To prevent direct laser irradiation to the electrostatic probe tip, a thin wire is installed in the laser channel to form a laser shadow for the probe tip. The ablation signal disappears when the probe tip is fully eclipsed by the laser shadow. The influence of a screening object on the signal intensity of LPD is investigated by experiments and model calculations. It is confirmed that the LPD signal intensity is accurately estimated when some conditions are satisfied, even when a part of the collection region of photodetached electrons is overlapped by the shadow. It is an ablation-free LPD method that can be used to evaluate the negative ion density at a sufficient laser power, even when the ablation disturbs the LPD signals in the conventional LPD technique.

A critical assessment of laser ablation ICP-MS as an analytical tool for depth analysis in silica-based glass samples

A. J. G. Mank and P. R. D. Mason, J. Anal. At. Spectrom., 1999, 14, 1143 DOI: 10.1039/A903304A

Element-selective trace detection of toxic species in environmental samples using chromatographic techniques and derivative diode laser absorption spectrometry

absorption per square root of detection bandwidth are obtained if sufficient laser power is available and if the absorption is also subject to additional modulation. The analytical versatility of these techniques is demonstrated by quantitative analysis of very low concentrations of (i) Cr(VI) species in tap water and (ii) chlorinated poly-aromatics (chlorophenols) in plant extracts, both after chromatographic separation. The atomic absorption measurements were performed in an air–acetylene flame (Cr) and in a low-pressure microwave-induced plasma (chlorophenols).

The Development for Quantitative Measurement Method of Soot Concentration Using LII. 1st Report. Evaluations of Fundamental Characteristics of LII and Correction method for Signal Attenuation.

The main factors which prevent quantitative soot measurements using laser-induced incandescence (LII) are expected to be as follows : laser intensity reduction due to soot clouds, LII signal attenuation due to soot clouds lying between the observation points and a camera and uncertainty of a relation between the signals and soot concentrations. To investigate the effects of these factors and solve these problems, LII was applied to a premixed flat flame where soot concentrations were measured in advance by transmissive light extinction method combined with computed tomography. The following points are clarified. (1) The correction on the incident laser attenuation is not necessary by using sufficient laser power because the LII signal saturates over a critical laser intensity. (2) The soot concentration is obtained from the LII signal by the calibration. (3) The signal attenuation can be corrected by multi-layer measurement tequnique using Lambert-Beer's law. Consequently, a quantification has been realized with accuracy of ±10% in this work.

Feasibility Study of Ge-Sb-Te Phase-Change Optical Disk Medium for One-Pass Overwrite Digital Audio Recording

A phase-change optical disk medium utilizing a Ge12Sb39Te49 memory film showed characteristics suitable for one-pass overwriteable digital audio disk system at a low linear velocity of 1.3 m/s. Applying the multipulse recording method, the eight to fourteen modulatlon (EFM) signals were successfully overwritten using only one laser beam with a small block error rate (BLER) of <50 counts/s. The laser irradiation power was typically 13 mW for the peak power level and 7 mW for the bias level. The available cycle number was observed to be more than 104 cycles with a practical sufficient laser power tolerance of + / -20%.

Low-power and high-stability SRAM technology using a laser-recrystallized p-channel SOI MOSFET

Laser recrystallization of p-channel SOI MOSFETs on an undulated insulating layer is demonstrated for SRAMs with low power and high stability. Self-aligned p-channel SOI MOSFETs for loads are stacked over bottom n-channel bulk MOSFETs for both drivers and transfer gates. A sufficient laser power assures the same leakage currents between SOI MOSFETs fabricated on an undulated insulating layer in memory cell regions and on an even insulating layer in field regions. The on/off ratio of the SOI MOSFETs is increased by a factor of 10/sup 4/, and the source-drain leakage current is decreased by a factor of 10-10/sup 2/ compared with those of polysilicon thin-film transistors (TFTs) fabricated by using low-temperature regrowth of amorphous silicon. A test 256-kb SRAM fabricated this technology shows improved stand-by power dissipation and cell stability. The process steps can be decreased to 83% of those TFT load SRAMs if both the peripheral circuit and memory cells are made with p-channel SOI and n-channel bulk MOSFETs. >

Efficient generation of nearly diffraction-free beams using an axicon

ZnSe axicon is used to efficiently generate approximations to diffraction-free Bessel function beams at λ = 10.6 μm. The central spot radius of ~ 170 μm generated when the axicon is illuminated by a plane wave is maintained for distances of up to 11 cm with sufficient laser power to allow drilling of plexiglass to be demonstrated.

Spectroscopic decay-rate measurements below the laser linewidth

When two levels can be strongly coupled by a pulsed laser, it is possible to measure the decay rate from the upper state by applying sufficient laser power to depletion broaden the transition. The depletion broadening is proportional to the square root of the decay rate times the total energy density of the laser pulse. With sufficient laser power, this technique can be used even if the decay rate is smaller than inhomogeneous broadenings or the laser linewidth. The technique is used here to measure autoionizing rates of some 6P((1/2))ns states.