We present novel frequency tuning methods for broadband mid-infrared spectroscopy that take advantage of the unique frequency sampling properties of our recently developed "nested dual-cavity doubly resonant optical parametric oscillator" (NesCOPO). These methods, referred to as Vernier frequency sampling, enable mode-hop tuning with an adjustable virtual-cavity intermode spacing. Both frequency
... [Show full abstract] resolution and span are widely adjustable and can be tailored to fulfill the requirements either for broadband spectroscopy (> 50 cm(-1) spectral coverage) at low resolution or for high resolution (< 0.01 cm(-1)) narrow band spectroscopy. The technique is applied to short-range (10 to 30 m) atmospheric CO2 measurements at 4.2 A mu m using integrated path differential absorption LIDAR.