Near-infrared thermal lens spectrometer based on an erbium-doped fiber amplifier and an acousto-optic tunable filter, and its application in the determination of nucleotides

A novel spectrometer that is based on the use of the thermal lens effect for sensitive measurements of absorption in the near-IR region has been developed. In this instrument the near-IR excitation light (from 1515 to 1590 nm) was provided by an erbium-doped fiber amplifier (EDFA). An acousto-optic tunable filter (AOTF) was used to spectrally disperse the light from the EDFA. The AOTF was used in a new configuration in which, instead of the diffracted light, the transmitted light was used. 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 sensitivity 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.