Laser beam path

Figure 5 shows the laser beam path reflected by the torsional cantilever. The incident angle is y on the cantilever surface before the cantilever torsion. When the torsional angle of the cantilever is 6i, reflection ray turned an angle a. Their relationship can be expressed by... 

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. 

Figure 13.40 Schematic layout of a LSUCLM system set-up. The excitation laser beam path is shown with a dotted line, and the emission pathway is shown in a solid line.

Let us now follow the laser beam path. The beam from a laser diode (1) is focused onto the back of the cantilever (3) with the help of a mirror (2). The beam reflects off the back of the cantilever onto a segment photodiode (5) with the help of another mirror (4). The amplified differential signal between the upper and lower photodiodes provides a sensitive measure of the cantilever deflection. 

Since spatial resolution is diffraction limited, short wavelength lasers are optimal for analyzing small sample features. In order to achieve micron-level spatial resolution, the alignment of the Raman microscope is critical. The visual light path, the excitation laser beam path, and the Raman scatter beam path from the sample to the detector must aU be targeted precisely on the same spot. 

Class 4 lasers produce high-power output, above 500 mW. Exposure to the direct beam, specular reflections, or diffuse reflections presents a hazard to both the eyes and skin. A Class 4 laser poses a Are hazard risk (radiant power >2 W/cm is an ignition hazard). These lasers can create hazardous airborne contaminants. They also pose a high-voltage electrical risk. Always enclose the entire laser beam path, if possible, or enclose most of the beam path to reduce the potential hazards. 

The vision system has no moving parts. The camera is attached to the laser rail and is optically in-line with laser beam path. A wavelength specific filter allows the camera to capture images without interfering with the... 

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