Multipass optical cell based upon two cylindrical mirrors for tunable diode laser absorption spectroscopy

A compact multipass optical cell based upon a front cylindrical mirror with a central input/output hole and a rear cylindrical mirror is described for application to tunable diode laser absorption spectroscopy. Rotation of the rear cylindrical mirror and small variations of the cell base length (~110 mm) have been used to achieve different spot patterns and path lengths. CO2 and CH4 direct absorption measurements using the developed cell with a fibre-coupled distributed-feedback laser at 1605.5 nm have been performed. A noise-equivalent absorption sensitivity of 2.5X10-8 cm-1Hz-1/2 has been determined for 138 passes in the cell and averaging of 2000 consecutive scans within 1.93 s.