Single-mode VCSELs for Interferometric Applications
An alternative application that, until now, could only be served by an HeNe laser.
VCSEL
Due to its coherence length, a single-mode VCSEL can be used in applications (for interferometric measurements and as a reference beam inside spectrometers) that, until now, could only be served by an HeNe laser. The advantages of using these VCSELs include the price, miniaturization, longer life expectancy, reduced power consumption, and a minimized thermal influence on the measurement system.
Due to the line width (delta f = 100 MHz) the coherence lengths (delta L) can be approximated to 1.5 m.
Delta L = 0.5 * c / delta f
c = speed of light
The model of a quasi monochromatic light source is used for this calculation (Haferkorn, Optik, S.99). Back reflections into the laser should be prevented and the power supply should be noise free as both of these effects increase the line width of the laser!
