Obviously, the choice of diffractometer for stress measurement depends largely on the type of sample to be studied, the type of other diffraction experiments to be performed, and the available budget. However, in most cases some basic requirements should be met, so the following requirements can be given.
It should be possible to reach a high diffraction angle of 2θ = 165°, and the diffractometer should at least allow the side tilt method by using optional accessories. In order to be able to analyze the real parts of larger samples or complex geometry attachments, samples that are easy to install and align should also be provided. The possibility of positioning the illuminated area with a Laser pointer or a long-distance microscope is usually of great advantage.
The determination criteria for using mobile devices to determine reliable and economical stresses are the size and weight of the device, the possibility of a rigid connection between the diffractometer and the component under test, and most importantly, simple alignment of the measuring point and direction.
The wavelength of the semiconductor laser covers the spectral region from 200 nm to 3 mm. Although the most common semiconductor lasers work in the near infrared region, such as InGaAlP/GaAs diodes (720–880 nm), InGaAsP/InP diodes (900–1100 nm) and AlGaAs/GaAs or InGaAsP diodes (1200–1650 nm), some others It produces red light (for example, in the GaInP and InGaAs/GaAs diodes in the 630-670 nm laser engraver) or blue or violet light (with gallium nitride). For mid-infrared emission, for example, there are GaSb-based structures and lead selenide (PbSe) lasers (lead salt lasers) (1870-2680 nm).
Quantum cascade lasers cover mid-infrared spectrum and far-infrared spectrum (3.5-24μm and 60μm-3 mm), and are widely used in the fields of sensing spectroscopy and subwavelength photonics. Their wavelength depends more on the geometry and size of their structure, rather than on the material. Optically pumped surface emitting semiconductor lasers can generate multi-watt output power with excellent beam quality even in mode-locked operation in the 570-2300 nm spectral range. The structure used is based on InGaP (~700 nm), GaAs (~800 nm), InGaAs (~1000 nm), GaInNAs (~1300 nm), InGaAsP (~1600 nm) and InGaAsSb (2200 nm). Using nonlinear crystals with external cavity configuration, they can generate harmonics, so they can cover the 250 nm spectral range (Eliseev, 1983; Sands, 2005; Seeger, 2004; Howieson et al., 2005; "Photonics" Open Access Encyclopedia). And laser technology, 2012; Capasso, 2010). Table 8.1 summarizes the typical wavelengths and general applications of different diode blue laser pointer.