Zhensong Cao

Ultrabroadband tunable continuous-wave difference-frequency generation in periodically poled lithium niobate waveguides

We report, for what is the first time to our knowledge, widely tunable mid-IR light generation over a range of greater than 1000 nm in the 4 microm region by employing a single quasi-phase-matched periodically poled niobate waveguide at room temperature. The waveguide we used was fabricated by annealed proton exchange based on periodically poled lithium niobate. A peak conversion efficiency of 10%/W and a linewidth as small as 37 MHz were achieved. The developed mid-IR light generator may find wide applications in trace gas detection of multiple atmospheric species and high-resolution spectroscopy.

Precise 13CO2/12CO2 isotopic ratio measurements for breath diagnosis with a 2-μm diode laser

A laser spectrometer based on a distributed-feedback semiconductor diode laser at 2 μm is developed to measure the changes of 13CO2/12CO2 isotope ratio in exhaled breath sample with the CO2 concentration of ~4%. It is characterized by a simplified optical layout, in which a single detector and associated electronics are used to probe CO2 spectrum. The cell has 10 cm long base length with 26.4 m optical path length in total and 330 cm3 volume. The cell pressure and temperature are controlled at 50 Torr and 28℃, respectively. The best 13δ precision of 0.06‰ was achieved by using wavelet denoising and Kalman filter.