Bluewave Tri-Laser Diffraction Technology
The Bluewave TRI-LASER Diffraction System developed by MICROTRAC allows light scattering measurements to be made from the forward low angle region to almost the entire angular spectrum (approximately zero to 160 degrees). It does so by a combination of three lasers (one red and two blue) and two detector arrays, all in fixed positions. The primary Red laser (on-axis) produces scatter from nearly on-axis to about 60 degrees, detected by a forward array and a high-angle array, both of which have logarithmic spacing of the detector segments. The second Blue laser (off-axis) is positioned to produce scatter beyond the 60 degree level which is detected using the same detector arrays. The third Blue laser (offaxis) is positioned to produce backscatter, again using the same detector arrays. This technique effectively multiplies the number of sensors that are available for detection of scattered light.
As particles become smaller they scatter light at higher angles but at significantly varying intensities. The power or intensity of scattered light has an inverse relationship to the fourth power of the wavelength of the incident light ( Ι = 1/λ4). By reducing the wavelength of the incident light by almost half from 780nm to 405nm, the amount of light scattered by the same particle is increased almost 16 times. In the TRI-LASER arrangement, lasers two and three are directed at the sample in such a way as to detect light scattered by smaller particles (if present) in angles between 60 and 160 degrees. By using Blue lasers in these positions the detected signals are enhanced to give unsurpassed sensitivity and resolution in the sub-micron region. The intensity of the incident light supplied by a Blue laser is significantly higher than that supplied by a Blue LED and the sensitivity of the measurement is increased accordingly.
Figure indicates the resolution of a Bluewave measurement for a mixture of 79nm, 220nm and 445nm polystyrene standards.