title: Integrated fiber optic incoherent broadband cavity enhanced absorption spectroscopy detector for near-IR absorption measurements of nanoliter samples.
abstract: An integrated fiber-optic sensor is described that uses incoherent broadband cavity enhanced absorption spectroscopy for sensitive detection of aqueous samples in nanoliter volumes. Absorption was measured in a 100 µm gap between the ends of two short segments of multimode graded-index fiber that were integrated into a capillary using a precision machined V-grooved fixture that allowed for passive fiber alignment. The other ends of the fibers were coated with dielectric mirrors to form a 9.5 cm optical resonator. Light from a fiber-coupled superluminescent diode was directly coupled into one end of the cavity, and transmission was measured using a fiber-coupled silicon photodiode. Dilute aqueous solutions of near infrared dye were used to determine the minimum detectable absorption change of 2.4×10(-4) under experimental conditions in which pressure fluctuations limited performance. We also determined that the absolute minimum detectable absorption change would be 1.6×10(-5) for conditions of constant pressure in which absorption measurement is limited by electronic and optical noise. Tolerance requirements for alignment are also presented.
authors.affiliation: Sandia National Laboratories, Livermore, California 94551, USA.
authors.forename: Anthony L
authors.initials: AL
authors.lastname: Gomez
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Renzi
authors.forename: Julia A
authors.initials: JA
authors.lastname: Fruetel
authors.forename: Ray P
authors.initials: RP
authors.lastname: Bambha
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000295:instrumentation*; D005336:Fiber Optic Technology / Q000295:instrumentation*; D057230:Limit of Detection; D008832:Microchemistry / Q000295:instrumentation; D055100:Optical Fibers; D004364:Pharmaceutical Preparations / Q000032:analysis; D019265:Spectroscopy, Near-Infrared / Q000295:instrumentation*
chemical_list: D004364:Pharmaceutical Preparations