Scanning Focused Laser Beam Research Articles

The Thinnest Light Disk: Rewritable Data Storage and Encryption on WS2 Monolayers

AbstractThe thinnest light disk is demonstrated at the atomic level by developing an erasable method to directly write encrypted information onto WS2 monolayers. The write‐in is realized by precise control of photoluminescence emission by means of ozone functionalization and scanning focused laser beam. The visual decryption and reading‐out of information are enabled by fluorescence contrast. The high encryption level is ensured by the threshold power upon which the data deletion will be triggered. Owing to the high spatial resolution and power sensitivity, the storage capacity within <1 nm thickness can be up to ≈62.5 MB cm−2, and the writing speed can reach ≈6.25 MB s−1. Density functional theory calculations suggest that the disk formatting is realized by ozone molecule adsorption induced localized unoccupied states, while the read‐in relies on the passivation of defects via substitution of the sulfur vacancies with oxygen atoms. The results of this study promote data storage and encryption on the atomic scale.

Microsteganography on WS2 Monolayers Tailored by Direct Laser Painting.

We present scanning focused laser beam as a multipurpose tool to engineer the physical and chemical properties of WS2 microflakes. For monolayers, the laser modification integrates oxygen into the WS2 microflake, resulting in ∼9 times enhancement in the intensity of the fluorescence emission. This modification does not cause any morphology change, allowing "micro-encryption" of information that is only observable as fluorescence under excitation. The same focused laser also facilitates on demand thinning down of WS2 multilayers into monolayers, turning them into fluorescence active components. With a scanning focused laser beam, micropatterns are readily created on WS2 multilayers through selective thinning of specific regions on the flake.

Enhanced Photoresponse from Phosphorene-Phosphorene-Suboxide Junction Fashioned by Focused Laser Micromachining.

Enhanced photoresponse is obtained from phosphorene-phosphorene-suboxide. A scanning focused laser beam is employed as a straightforward approach to convert part of a phosphorene film into phosphorene suboxide, creating a functional junction in situ on an optoelectronic device based on phosphorene. As a result, the photoelectrical properties of the optoelectronic device are significantly improved.

Laser modified ZnO/CdSSe core-shell nanowire arrays for Micro-Steganography and improved photoconduction.

Arrays of ZnO/CdSSe core/shell nanowires with shells of tunable band gaps represent a class of interesting hybrid nanomaterials with unique optical and photoelectrical properties due to their type II heterojunctions and chemical compositions. In this work, we demonstrate that direct focused laser beam irradiation is able to achieve localized modification of the hybrid structure and chemical composition of the nanowire arrays. As a result, the photoresponsivity of the laser modified hybrid is improved by a factor of ~3. A 3D photodetector with improved performance is demonstrated using laser modified nanowire arrays overlaid with monolayer graphene as the top electrode. Finally, by controlling the power of the scanning focused laser beam, micropatterns with different fluorescence emissions are created on a substrate covered with nanowire arrays. Such a pattern is not apparent when imaged under normal optical microscopy but the pattern becomes readily revealed under fluorescence microscopy i.e. a form of Micro-Steganography is achieved.

Microstructure of selective laser melted nickel–titanium

In selective laser melting, the layer-wise local melting of metallic powder by means of a scanning focused laser beam leads to anisotropic microstructures, which reflect the pathway of the laser beam. We studied the impact of laser power, scanning speed, and laser path onto the microstructure of NiTi cylinders. Here, we varied the laser power from 56 to 100W and the scanning speed from about 100 to 300mm/s. In increasing the laser power, the grain width and length increased from (33±7) to (90±15) μm and from (60±20) to (600±200) μm, respectively. Also, the grain size distribution changed from uni- to bimodal. Ostwald-ripening of the crystallites explains the distinct bimodal size distributions. Decreasing the scanning speed did not alter the microstructure but led to increased phase transformation temperatures of up to 40K. This was experimentally determined using differential scanning calorimetry and explained as a result of preferential nickel evaporation during the fabrication process. During selective laser melting of the NiTi shape memory alloy, the control of scanning speed allows restricted changes of the transformation temperatures, whereas controlling the laser power and scanning path enables us to tailor the microstructure, i.e. the crystallite shapes and arrangement, the extent of the preferred crystallographic orientation and the grain size distribution.

Direct laser micropatterning of GeSe2 nanostructures film with controlled optoelectrical properties

We demonstrate that a direct focused laser beam irradiation is able to achieve localized modification on GeSe2 nanostructures (NSs) film. Using a scanning focused laser beam setup, micropatterns on GeSe2 NSs film are created directly on the substrate. Controlled structural and chemical changes of the NSs are achieved by varying laser power and the treatment environment. The laser modified GeSe2 NSs exhibit distinct optical, electrical and optoelectrical properties. Detailed characterization is carried out and the possible mechanisms for the laser induced changes are discussed. The laser modified NSs film shows superior photoconductivity properties as compared to the pristine nanostructure film. The construction of micropatterns with improved functionality could prove to be useful in miniature optoelectrical devices.

In-situ guidance of individual neuronal processes by wet femtosecond-laser processing of self-assembled monolayers.

In-situ guidance of neuronal processes (neurites) is demonstrated by applying wet femtosecond-laser processing to an organosilane self-assembled monolayer (SAM) template. By scanning focused laser beam between cell adhesion sites, on which primary neurons adhered and extended their neurites, we succeeded in guiding the neurites along the laser-scanning line. This guidance was accomplished by multiphoton laser ablation of cytophobic SAM layer and subsequent adsorption of cell adhesion molecule, laminin, onto the ablated region. This technique allows us to arbitrarily design neuronal networks in vitro.

Localised laser joining of glass to silicon with BCB intermediate layer

The use of a laser to provide localised heating is an ideal solution to the problem of packaging micro-electro-mechanical-systems (MEMS) whilst maintaining a low device temperature to avoid changes in temperature-sensitive materials in the device. In this paper we present localised laser bonding of glass to silicon (normally used as the MEMS substrate) by using a fibre-delivered high power laser diode array to cure an intermediate layer of the thermosetting polymer Benzocyclobutene (BCB). In our experiments, we use two techniques to realise localised heating: one is to use an axicon together with a conventional positive lens to generate a ring focus; the other is to use a scanning focused laser beam. In both cases localised cooling is required to confine the elevated temperatures to the bonding area. Finite Element (FE) simulation indicates that both techniques should keep the temperature in the centre of the package to approximately that of the ambient environment (300 K) during the process. However, experiments show that the temperature in the centre of the package rises to a value of around 500 K, likely due to poor contact between silicon and cooling sink. Experimentally, we confirmed that either technique can be used to obtain excellent bonding of glass to silicon with leak rate at a level of 10−10 mbar l s−1, whilst keeping the centre of device at a lower temperature.

超伝導体 Ｂｉ系超電導圧粉体へのレーザ照射処理

The bulk sample simply produced by pressing calcined superconductor powder shows no superconductive properties. Laser scan transforms however such non-superconducting bulk material into superconductive one partially along the scanned area. The goal of this study is to make superconductive circuits on the surface of the(Bi 2223 system)non-superconductive bulk by scanning focused laser beam as designed. This paper reports the effect of 150W CO2 laser irradiation on the superconducting property of the bulk by changing the following conditions: beam scan speed (bss), beam scan times(bst)and assist gas pressure(agp).The best result of Tc(end)=66.5 K was obtained when the laser irradiation was performed with bss=10 mm/min, bst=1 stroke and agp=49 kPa. Superconductive crystals were grown at the laser irradiated area with depth of-300μm. The crystals were oriented to the same direction of the beam scan.

Optical Creation of Radiophotoluminescence Centres in Dosemeter Glass By Two-Photon Absorption

In recent years considerable progress has been achieved in the field of phosphate glass dosimetry through the evolution of improved glass material with good batch uniformity, newly designed dosemeter encapsulation and automatic readout techniques based on pulsed UV laser excitation. The peak intensity of the laser pulses exceeds the range of intensity available with conventional UV light sources. This paper reports on effects that may occur when an intense light source is used for RPL readout. In a specially designed reader unirradiated flat RPL glasses and a scanning focused laser beam for RPL readout were used. The influence of intense UV laser excitation on RPL readout intensity has been studied for dependence on the intensity and duration of excitation. The experimental arrangement, the scanning procedure for laser excitation, the dosemeter glass handling and the method of RPL readout are described. The observed RPL intensity is attributed to the optical creation of RPL centres by two-photon absorption in the focal region of the laser beam. By means of beam profile and power measurements an estimation of the lower limit of excitation intensity is given where two-photon absorption becomes important.

Calculation of the effects of a focused laser beam on the dynamic Josephson tunneling states

Perturbative calculations of the voltage response of constant-current biased Josephson tunnel junctions to a focused laser beam have been performed. The dependence of the voltage modification as a function of the laser beam position was calculated. The results were found to be qualitatively different for junctions biased on the first zero-field current step but with either vortex-mode or cavity-mode excitations. Therefore, the recently developed scanning focused laser beam technique operated in this mode can be a simple and effective method for probing the nature of the dynamic Josephson tunneling state.