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Handbook Of Shaft Alignment Episode 1 Part 10

Tham khảo tài liệu 'handbook of shaft alignment episode 1 part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 240 Shaft Alignment Handbook Third Edition How semiconductor junction diode lasers work Junction n-Type semiconductor p-Type semiconductor Current must be high enough for electrons to move from a higher to a lower energy level in the junction Battery positive Collimated light beam - Photono - - I-Photon Photon f . Electron O Electron Hole Hole Photon Partially reflective facets on both sides of the edge of the chip act as an optical resonance chamber Battery negative - Cross-sectional structure of a 670 nm GaInP semiconductor laser p-GaAs cap layer n-GaAs backing p- Gai-x Alp0.5 0.5P Ga0.5 0.5 P n- Gai-x Alx o.5 h.5P GaAs n-GaAs substrate The chemical composition of the semiconductor determines the wavelength of light emitted from the laser. Near infrared lasers used for alignment measurement devices are made from gallium-aluminum-arsenide 620-895 nm . Visible red lasers are made from gallium-indium-phosphorous 670 nm . FIGURE 6.27 How semiconductor laser diodes work. about 1.5 mm approximately 60 mils in diameter as it exits the diode and is collimated i.e. focused since only one side of the diode actually allows the light to exit. After exiting the diode if the light beam was in a pure vacuum the beam would stay focused for long distances. However since there are small molecules of water vapor in the air we breathe Shaft Alignment Measuring Tools 241 Cathode Anode 20 X 20 mm 10 X 10 mm FIGURE 6.28 How photodiodes work. the light from the laser is diffracted as it passes through each molecule of water vapor diffusing the beam. Typically the useable distance of laser is somewhat limited to 30 ft due to the diffraction of the beam. Since the laser beam is around 60 mils in diameter as it exits the diode the measurement accuracy would only be 60 mils i.e. about 1 16th of an inch if just the laser beam were solely used as the measurement device. This accuracy is just fine for laser levels when constructing buildings for example but since we are looking for accuracies