Dynamic resonant peak locking scheme for diode laser modulation spectroscopy

We describe a diode laser frequency control scheme that dynamically locks the laser to an absorption resonance line while simultaneously allowing the quantitative measure of absorption strengths as weak as a few parts in 106. The method exploits a novel modulation scheme, and is capable of locking the laser to both stable and transient species in an electrically noisy environment such as that found in plasma etching reactors. We present an experimental demonstration using a lead salt diode laser operating near an rt plasma etching diode reactor and in an industrial-type triode reactor.