NEAR-INFRARED THERMAL LENS SPECTROMETER BASED ON AN ERBIUM-DOPED FIBER AMPLIFIER AND AN ACOUSTOOPTIC TUNABLE FILTER, AND ITS APPLICATION INTHE DETERMINATION OF NUCLEOTIDES

A novel spectrometer that is based on the use of the thermal lens effe ct for sensitive measurements of absorption in the near-m region has b een developed. In this instrument the near-IR excitation light (from 1 515 to 1590 nm) was provided by an erbium-doped fiber amplifier (EDFA) . An acousto-optic tunable filter (AOTF) was used to spectrally disper se the light from the EDFA. The AOTF was used in a new configuration i n which, instead of the diffracted light, the transmitted light was us ed. The heat generated as a consequence of the absorption of the near- IR excitation beam by the sample was monitored by a He-Ne laser. The s ensitivity of this spectrometer was found to be at least two to three times higher than that of conventional transmission measurements. Its application in the sensitive determination of nucleotides (adenosine, cytidine, guanosine, and thymidine) is described. (C) 1997 Optical Soc iety of America.