Ppb-level detection of nitric oxide using an external cavity quantum cascade laser based QEPAS sensor Dong, Lei ; Spagnolo, Vincenzo ; Lewicki, Rafał ; Tittel, Frank K. Abstract Publication: Optics Express Pub Date: November 2011 DOI: 10.1364/OE.19.024037 Bibcode: 2011OExpr..1924037D