Vector noise subtraction in vapor cell spectroscopy

A method, comprising:

• modulating input light to generate a modulated pump optical signal;
• transmitting the modulated pump optical signal and an unmodulated reference optical signal through a vapor cell in a spectroscopy system using separate and non-crossing optical paths;
• determining amplitude filter parameters from optical signals resulting from transmitting the modulated pump optical signal and the unmodulated reference optical signal through the vapor cell;
• determining a phase difference from the resulting optical signals, wherein determining the amplitude filter parameters and the phase difference is performed during a calibration phase, the method further comprising, during an operational phase:
• detecting a first optical signal resulting from the unmodulated reference optical signal passing through the vapor cell and a second optical signal resulting from the modulated pump optical signal passing through the vapor cell;
• phase shifting at least one of the first or second optical signals based on the phase difference;
• scaling at least one of the first or second optical signal based on the amplitude filter parameters;
• and
• performing vector subtraction of the first optical signal and the second optical signal to suppress noise.

A spectroscopy system, comprising:

• a first vapor cell configured to receive as an input an unmodulated reference optical signal;
• a second vapor cell configured to receive as an input a modulated pump optical signal;
• and
• a control system configured to:
• detect a first optical signal resulting from the unmodulated reference optical signal passing through the first vapor cell and a second optical signal resulting from the modulated pump optical signal passing through the second vapor cell, and
• perform a vector subtraction of the first optical signal and the second optical signal to suppress noise.