Laser sensor module for particle density detection

A laser sensor for detecting a particle density, the laser sensor comprising:

• at least a first laser configured to emit a first light or laser beam,
• an optical arrangement arranged to focus at least the first light or laser beam to a first measurement volume, wherein the optical arrangement has a first numerical aperture with respect to the first light or laser beam,
• at least a first detector configured to determine a first interference signal, and
• an evaluator, wherein the evaluator is configured to receive detection signals generated by at least the first detector in reaction to the determined first interference signal, wherein the evaluator is further configured to determine an average transition time of particles passing the first measurement volume in a predetermined time period based on a duration of the first interference signals generated by the particles, wherein the evaluator is further configured to determine a number of particles based on the first interference signals in the predetermined time period, and wherein the evaluator is further configured to determine a first particle density based on the average transition time and the number of particles.

A method of particle detection, the method comprising:

• emitting at least a first light or laser beam by a first laser,
• focusing the first light or laser beam with a first numerical aperture,
• determining a first interference signal or a first self-mixing interference signal of a first optical wave within a first laser cavity of the first laser,
• determining an average transition time of particles passing the first measurement volume in a predetermined time period based on a duration of the first interference signal or the first self-mixing interference signals generated by the particles,
• determining a number of particles based on the first interference signal or the first self-mixing interference signals in the predetermined time period, and
• determining a first particle density based on the average transition time and the number of particles.