Patent ID: 8390813

Claim:
A system for monitoring stable isotopes from a sample of gas comprising: a cell for receiving a sample of gas, a pump for sending the sample of gas into the cell, a tunable diode laser for providing a laser beam having an original carrier frequency (ω c ), a modulation source operating in the radiofrequency regime for modulating the original carrier frequency (ω c ) of the laser beam from the tunable diode laser, thereby producing a modulated laser beam having the original carrier frequency (ω c ) and sidebands on either side of and evenly spaced apart from the carrier frequency by a modulation frequency (ω m ), the modulated laser beam directed at a sample of gas inside the cell, a detector for providing a detection signal from a stable isotope from the gas sample inside the cell, said detector comprising a reference channel and a signal channel, an amplifier for amplifying the detection signal from said detector, an optical fiber for transmitting light from the multipass cell to the signal channel of said detector, a focusing means for focusing light from the cell into the optical fiber, a beamsplitter for directing the modulated laser beam simultaneously to the cell and to the reference channel of the detector, and a polarizer for adjusting fractions of modulated laser light directed to the cell and the reference channel of the detector via the beamsplitter, wherein the system lacks a reference cell and is configured such that said beamsplitter splits the modulated laser beam into a reference beam and a signal beam, wherein said reference beam is sent directly to the reference channel of the detector and said signal beam is sent to said cell containing a sample of gas and afterward to the signal channel of the detector.