Directly modulated diode laser frequency doubled in a KTP waveguide as an excitation source for CO2 and O2 phase fluorometric sensors

A directly modulated infrared diode laser was frequency doubled in an intracavity KTP quasi-phase matched waveguide, producing modulated laser light at 425 nm, which was subsequently employed for phase fluorometric detection of CO2 and O2 gases. The frequency-doubled source was coupled to a single optical fiber to deliver the excitation light to the sensor mounted at the fiber tip. Fluorescence from the sensor returned through the same fiber to a photodetector. This compact, low-power source provided continuously tunable modulation frequencies up to 200 MHz. In the detection of CO2 , the doubled infrared diode laser produced 425-nm light that was modulated to a depth of 27% at a modulation frequency of 95 MHz.