Thermal lens spectroscopy using a diode laser and optical fibers

A compact thermal lens spectrometer was developed using optical fibers and a diode laser for measurements of rare earth species in aqueous solutions. A cw GaAlAs diode laser coupled with a multimode step-index fiber was used as the excitation source. The thermal lens was probed with a He-Ne laser using a multimode 200 μm diameter core optical fiber as the aperture and to transmit the probe beam to the detector. The system was tested for the detection of Nd3+ in aqueous solutions at 794.6 nm. A sensitivity with detection limit of 79±4 M−1 and 8×10−5 M was obtained for an incident power of 10 mW and a power density of 11 W/cm2.