Optical sensor for phase determination

An apparatus for in-situ phase determination, the apparatus comprising:

• a measurement chamber configured to retain a substance;
• an entrance window mounted on a side of the measurement chamber;
• an exit window mounted on an opposite side of the measurement chamber, the exit window being parallel with the entrance window;
• a light source configured to generate an incident light beam, the incident light beam being directed to the entrance window at a non-zero angle of incidence with respect to a normal of the entrance window, the incident light beam passing through the entrance window, the measurement chamber and being reflected on the exit window to form a reflected light beam;
• and the reflected light beam passing through the measurement chamber and the entrance window;
• and
• a detector mounted above the entrance window, the detector being configured to receive the reflected light beam passing through the entrance window and generate measurement data.

A method for in-situ phase determination, the method comprising:

• directing an incident light beam to an entrance window of a measurement chamber at a non-zero angle of incidence with respect to a normal of the entrance window, the entrance window being mounted on an side of the measurement chamber, and the measurement chamber retaining a substance;
• collecting, via a detector, an output light beam, the incident light beam passing through the entrance window, the measurement chamber, and an exit window to form the output light beam, the exit window being mounted on an opposite side of the measurement chamber and parallel with the entrance window, and the detector being positioned under the exit window;
• generating, by processing circuitry, a measurement data that registers a beam centroid position of the output light beam;
• determining a property of the substance retained in the measurement chamber based on the measurement data;
• and
• controlling a manufacturing process based on the determined property.