Scanned Laser Research Articles

Scanning Optics Enabled Possibilities and Challenges in Laser Cladding

Laser cladding using a scanned beam is quite a similar process than laser cladding using static optics (e.g. lens or mirror optics). The main difference comes from the manipulation of the laser beam. In laser cladding with scanning optics the laser beam is manipulated with a scanner so that the laser's area of influence can be shaped numerically. This increases cladding process flexibility. Scanning optics enable laser beam modification considerably versatile way than normal static optics can. This is due to possibility of numerical adjustment of scanning amplitude, laser power and scanning frequency. By modifying these parameters clad beads geometry can by modified quite freely. However scanned laser beam in surface modification process creates some restricting factors to the process. Mainly limitations for the process parameter values come from the dual characteristics of the energy input. This paper treats usability of scanning optics in laser cladding process in general level. In this paper is discussed how scanned beam can be used to increase the flexibility but also maters that limit the usage of scanned beam in cladding process. Process possibilities and limitations are presented in trough experimental data and examples.

47.4: Invited Paper: 3D Displays using Scanning Laser Projection

AbstractScanning laser projection technology is enabling advances in a number of areas of 3D display development. We discuss various scanned laser display technologies developed in our laboratory: 1) Our 1 mm × 9 mm projector uses a vibrating singlemode optical fiber to produce scanned images, and enables compact 3D head‐mounted displays with the potential form factor of a pair of eyeglasses. 2) Arrays of scanning fiber projectors can enable massively‐multi‐view autostereoscopic displays with full head motion parallax and partial accommodation cues, and 3) Our 3D volumetric displays triaxially scan light beams to render a volume, placing different pixels at different optical viewing distances to enable accurate accommodation and vergence cues.

Vision with a scanning laser display: comparison of flicker sensitivity to a CRT

Laser scanning displays allow for large depth-of-focus, reduced optical aberrations, and high luminance. However, scanned laser light images have no phosphor persistence. Psychophysical tests with a 3-color laser display showed that flicker thresholds were nearly equal with a laser display relative to the CRT when both were matched in luminance, resolution, frame rate, and similar chromaticity. The threshold ratio was 1.14 (range 0.7–1.6). Differences in flicker sensitivity between displays were significantly related to the absolute energy at the cornea irrespective of the subjective luminance match. Flicker sensitivity was not enhanced by a laser scanning display without image persistence.

Use of scanned laser annealing to control the bamboo grain length of Cu interconnects

Microstructural evolution induced by scanned laser annealing (SLA) of Cu interconnects was found to produce unique large-grained “bamboo” grain structures, with bamboo grain lengths up to ten times the linewidth. These bamboo grain lengths are shown to depend on the scan rate and laser power. By comparing results from experiments on different structures with grain growth simulations, the bamboo grain length induced by SLA is shown to be a strong function of the thermal profile, where steeper thermal profiles yield longer bamboo grains.

Microscopy

Microscopy

Microstructural evolution induced by scanned laser annealing in Al interconnects

A method has been developed for inducing controlled microstructural evolution in thin films patterned into lines, using scanned laser annealing (SLA). Experimental studies show at least three distinct types of microstructures resulting from SLA, depending on the scan rate and laser power. Starting with a polygranular initial microstructure, scanned laser annealing leads to either a large-grained polygranular structure, a bamboo structure, or an agglomerated structure. Microstructural evolution induced by SLA was found to lead to different evolution than conventional annealing, as well as to produce unique large-grained “bamboo” structures. Simulations of SLA further suggest the possibility of producing near-single crystal microstructures under properly controlled conditions.

Scanning microphotolysis: a new photobleaching technique based on fast intensity modulation of a scanned laser beam and confocal imaging.

The fluorescence photobleaching method has been widely used to study molecular transport in single living cells and other microsystems while confocal microscopy has opened new avenues to high-resolution, three-dimensional imaging. A new technique, scanning microphotolysis (Scamp), combines the potential of photobleaching, beam scanning and confocal imaging. A confocal scanning laser microscope was equipped with a sufficiently powerful laser and a novel device, the 'Scamper'. This consisted essentially of a filter changer, an acousto-optical modulator (AOM) and a computer. The computer was programmed to activate the AOM during scanning according to a freely defined image mask. As a result, almost any desired pattern could be bleached ('written') into fluorescent samples at high definition and then imaged ('read') at non-bleaching conditions, employing full confocal resolution. Furthermore, molecular transport could be followed by imaging the dissipation of bleach patterns. Experiments with living cells concerning dynamic processes in cytoskeletal filaments and the lateral mobility of membrane lipids suggest a wide range of potential biological applications. Thus, Scamp offers new possibilities for the optical manipulation and analysis of both technical and biological microsystems.

Polarization Raman microprobe analysis of laser melting and etching in silicon

Polarization Raman microprobe spectroscopy is used to study crystalline silicon heated to the melting point by a tightly focused cw laser beam, which is either fixed or scanned across the surface. By examining optical phonons in solid silicon, the real-time Raman spectrum monitors the progress of silicon flow during melting and the trench depth during melt-assisted etching. Raman peaks lie between 482 cm−1, which is the Raman shift for silicon uniformly heated to the melting point (1690 K), and ∼510 cm−1, which is the Raman shift for c-Si heated just to the melting point and probed by the same beam. During laser melting with a static laser, the Raman spectrum of scattered light with z(x,y)z̄ polarization has two peaks, while the z(x,x)z̄ spectrum has one peak. This shows that at the beginning of melting in vacuum by a static laser there is a central region with solid silicon floating in the melt, which is surrounded by hot solid material. Because of the flow of the molten semiconductor, the temperature profile changes, causing the Raman spectrum to change rapidly. Laser melting of c-Ge and thin films of silicon in vacuum is also studied, as is the melting of c-Si by a static laser in the presence of an inert buffer gas. The presence of an inert buffer is shown to affect the temperature profile very strongly during melting and also during laser heating at lower laser powers when no melting occurs. During scanned laser melting and etching, the Raman spectrum has a single peak using either polarization configuration. Raman analysis during melting of silicon by a scanning laser shows that the average temperature in the probed region is much higher when there is a gas-phase argon buffer present (and no etching) than when there is an etching mixture of argon/chlorine gas (and etching). Along with these real-time Raman measurements, the reflection of the incident laser was monitored, and post-process Raman analysis and profilometry were also performed to characterize surface changes due to melting and etching.

Scanning laser system for combined fluorescent diagnostics and photodynamic therapy: structural design, preliminary trials, and potentials

Photodynamic therapy (PDT) is commonly performed by administration of porphyrin photosensitizers selectively retained by malignant tumors. Subsequent photoexcitation with UV-blue light causes fluorescence useful for diagnosis. Excitation by red light destroys the cancer tissue. The use of high-speed scanning of laser light as an alternative to conventional PDT which employs dispersed light to achieve uniformity of treatment is proposed. It is shown that treatment with scanned light beams produces photochemical effects in malignant animal tissue that are virtually the same as those caused by comparable treatments with diffused light. It is argued that undesirable thermal effects can be reduced by the use of focused, scanned laser beams in lieu of diffused light. It is also shown how concurrent analysis and treatment can proceed using a system of two laser beams.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A fast flat‐bed laser scanner for the digital acquisition of two‐dimensional electrophoresis patterns

AbstractAnalysis of two‐dimensional electrophoresis patterns demands computer assistance. Specialized machines to read and store the pattern of an autoradiograph or of a “wetgel” into a digital memory are rare. A fast and flexible opto‐mechanical picture reading and storage machine, specially designed for the computer‐aided analysis of two‐dimensional electrophoresis patterns, has been constructed. It is now possible to digitize, for example, a picture of 250 × 400 mm into pixels of ca. 250 × 250 μm with a grey level resolution of 8‐bit within 70 s. Digitizing at significant pixel sizes down to 64 μm is possible at correspondingly longer acquisition times for the areas to be digitized. The design is a flat‐bed scanner. One axis is scanned optomechanically (Galvanometer scanned laser beam), the other axis is scanned mechanically. The area covered by the scanning laser beam has a size of 250 × 400 mm or smaller. The control of the scanner, including pixel density and sampling synchronization is executed by a microprocessor system.

Metal Silicon Reactions Induced by CW Scanned Laser and Electron Beams

Scanned CW‐laser and electron beams have been utilized to react thin metal films of Pd, Pt, Mo, W, and Nb deposited by electron beam evaporation onto single crystal silicon substrates to form silicides. Formation of large area uniform layers of or is controlled by selection of the power level of the scanning laser or electron beam. Single phase , , and are also found after CW‐beam reaction. For the Pt/Si system mixed phase silicides are found after CW‐laser reaction with a superconducting metastable compound, , observed as the dominant phase. In contrast, single‐phase is found after electron‐beam reaction. Comparison is also made with electron beam evaporated films and argon sputter‐deposited films.

Measurement of Phase Boundary Dynamics During Scanned Laser Crystallization of Amorphous Ge Films

ABSTRACTTwo techniques have been used to measure the velocity of the amorphous-crystalline boundary during scanned laser crystallization of amorphous Ge films on fused-silica substrates. Values in the vicinity of 200 cm sec-1 have been measured by both methods. The results obtained by the first technique, an optical transmission method, confirm our theoretical model for the periodic motion of the boundary. The measurements made by the second technique, which is based on an examination of the structural features obtained at laser scanning rates up to about 600 cm sec-1 , show the boundary velocity to be rather insensitive to film thickness and background temperature. Controlled crystallization is expected to require stability of the laser beam power.

Scanning laser infrared microscopy of doping inhomogeneities in InAs single crystals

A scanned laser infrared microscope operating at 3.39 μm has produced optical transmission images of n-type InAs with free carrier concentrations ranging from 4.6 × 10 17/cm 3 to 2.4 × 10 18/cm 3. Variations in these infrared images are explained in terms of the Burstein effect. Images of normally opaque lightly-doped InAs have been produced by temperature-shifting the fundamental absorption edge wavelength. The optical perfection of both lightly- and heavily-doped n-type InAs were thus uniquely determined over large sample volumes.

Scanned Laser Infrared Microscope

In examination of ir-transmitting materials, internal irregularities and inclusions of foreign material can be detected by their effect upon the ir transmittance of the material. A scanning laser ir microscope has been constructed which produces, on an oscilloscope display, a shadowgraph picture of the ir transmittance of the material under examination. The 3.39-micro emission of a He-Ne laser serves conveniently as the ir source since many materials of interest transmit at this wavelength. The scan consists of a raster of 400 lines, and is completed in 1 sec. The detector is a room temperature operated indium arsenide photovoltaic cell, with a time constant of 2 microsec. A sample area of 1.2 cm x 1.2 cm is scanned with a focused spot having a nominal diameter of approximately 0.003 cm. The optical and electromechanical features of the microscope are described, and its application to examination of semiconductor materials is illustrated by several typical examples.