Time-domain terahertz measurement system having a single reference surface

A time-domain terahertz measurement system that measures a thickness profile of a sample, comprising:

• a scanning frame;
• a single reference surface;
• a terahertz transmitter that outputs terahertz interrogation pulses into a sample area between the terahertz transmitter and the single reference surface at a first time, Ta, when no sample is present in the sample area, and that outputs terahertz interrogation pulses into the sample area at a second time, Tb, when the sample is present in the sample area;
• and
• a controller that acquires an air scan profile including pulses reflected from the single reference surface corresponding to the interrogation signals output at the first time, Ta, and that acquires a sample scan profile including pulses reflected from the single reference surface corresponding to the interrogation pulses output at the second time, Tb, and including pulses reflected from the sample corresponding to the interrogation pulses output at the second time, Tb;
• wherein the controller further acquires air distance measurements including pulses reflected at a first reference point xA on the single reference surface corresponding to the interrogation pulses output at the first time, Ta, and at the second time, Tb and including pulses reflected at a second reference point xB on the single reference surface corresponding to the interrogation pulses output at the first time Ta, and at the second time, Tb;
• wherein the first reference point xA and the second reference point xB are points on the single reference surface that are outside of the sample area;
• wherein the controller further calculates a corrected air scan profile by performing a correction of the air scan profile received at the first time, Ta, based on the air distance measurements at points xA and xB received at the first time, Ta, and at the second time, Tb, and determines the thickness profile of the sample based on the corrected air scan profile and the sample scan profile.