Computer-controlled lasers

Development continues as an example—there is a move away from organic solvents to aqueous developers. The use of silver halide photographic film for imaging has been replaced by computer-controlled laser scanning. 

Computer control Laser, gas pressure, heater, target, up to 11 consecutive steps... 

The unit operates under computer control. Laser temperature and current selections for each species are input to the computer. The system is then switched to automatic mode and can operate unattended for at least 24 hours. 

A computer-controlled laser beam forms an image on a charged photosensitive drum. A carbon toner is applied and adheres to the charged areas, developing the image which is then transferred to the substrate and fixed with heat and pressure. Text, graphics and bar codes can all be produced this way. 

In the SLS process, a computer-controlled laser beam sinters selected areas of multiple layers of loosely compacted powder, e.g., plastic, metal, ceramic, or wax, layer-by-layer, imtil the article is completely built-up. The SLS procedure has been described in more detail (23). 

Fig. 5.58. (a) Schematic diagram of computer-controlled laser spectrometer with frequency marks provided by two FPI with slightly different free spectral ranges and a lambdameter for absolute wavelength measurement, (b) Scheme for wavelength determination according to (5.93c)... 

Another technique for the generation of via holes is the use of a computer-controlled laser. This procedure is being used in industries that require a wide variety of parts or parts with varied hole patterns. One equipment manufacturer " claims that with a single head system, via diameters from 50 to 350 pm (0.002 to 0.007 in.) can be laser drilled in tapes up to 1.016 mm (0.040 in.) thick at a rate of 30 holes per second. With this system it is very easy to reprogram the computer to generate any hole pattern desired. Care must be taken to assist the removal of the debris generated so that it does not recondense on the surface of the tape-cast material. 

A laser printer for computers works almost the same way. A computer-controlled laser "scans" (see Index if necessary) finely focused light across the cylinder, turning this laser on or off for each tiny spot ("pixel"). The black powder ("toner") can be the same material as in the photocopier, and the paper can also be the same. Together, the photocopier and laser printer have made a veritable revolution in the efficiency of office work. 

Stereolithography (SLA) is an additive method and uses a liquid-based systan. The liquid polymer is photocured layer by layer. The liquid polymers are (UV) ultraviolet-curable photopolymer (thermoset) resins such as epoxy, acrylates, and vinyl ethers. The system is illustrated in Figure 15.7. A tub (vat) is filled with the liquid resin. A platform supports the model as it is built. The platform is first raised to just below the liquid surface at a depth of the first layer to be cured. Then a computer-controlled laser is focused so that it solidifies the first layer to the required depth as it is moved in the x, y directions within the 2D area of the first slice. Subsequently, the platform is lowered a distance equal to the second layer thickness to be cured and the process is continued. Layer thicknesses as small as 0.025 mm (0.001 in.) up to 0.5 mm (0.020 in.) can be cured in this manner. 3D Systems is the company that supplies its patented SLA equipment to a worldwide market. 

A versatile Laser-SNMS instrument consists of a versatile microfocus ion gun, a sputtering ion gun, a liquid metal ion gun, a pulsed flood electron gun, a resonant laser system consisting of a pulsed Nd YAG laser pumping two dye lasers, a non-resonant laser system consisting of a high-power excimer or Nd YAG laser, a computer-controlled high-resolution sample manipulator on which samples can be cooled or heated, a video and electron imaging system, a vacuum lock for sample introduction, and a TOF mass spectrometer. 

In Table 4.3, the Cetac product LSX-200 is the specialized system for coupling with the ICP customer s system. It includes the laser, optical viewing system for exact positioning of the laser focus on a sample surface, and the sample cell mounted on the computer controlled XYZ translation stage. The system is also provided with the appropriate gas tuhing for transport of the ablated material into an ICP-OES/MS. 

A computer-controlled motorized translation stage mounted with a retro-reflector is used to vary the pump laser beam path relative to the probe laser beam path and this controls the relative timing between the pump and probe laser beams. Note that a one-foot difference in path length is about 1 ns time delay difference. The picosecond TR experiments are done essentially the same way as the nanosecond TR experiments except that the time-delay between the pump and probe beams are controlled by varying their relative path lengths by the computer-controlled motorized translation stage. Thus, one can refer to the last part of the description of the nanosecond TR experiments in the preceding section and use the pump and probe picosecond laser beams in place of the nanosecond laser beams to describe the picosecond TR experiments. 

The output of a Nd YLF laser is focussed by a series of lenses to a spot size of 0.5 pm upon a sample which may be positioned by an x-y-z stepping motor stage and scanned by a computer-controlled high frequency x-y-z piezo stage. Ions are accelerated and transmitted through the central bore of the objective into a time-of-flight (TOF) mass spectrometer. The laser scans an area of 100 x 100 pm with a minimum step size of 0.25 pm. TOF mass spectra of each pixel are evaluated with respect to several ion signals and transformed into two-dimensional ion distribution plots. 

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