Research on a small-volume portable non-contact chlorophyll-b measurement instrument based on laser spectroscopy

In this paper, a novel portable instrument for non-contact chlorophyll-b measurement is presented based on laser spectroscopy. In this instrument, a semi-conductor laser at the wavelength of 405 nm is selected as the excitation source. The laser power can be adjusted from 0 to 500mW at the pulsed repetition frequency (25Hz). The leaf excited by laser can generate chlorophyll-a fluorescence at the peak wavelength of 695 nm and chlorophyll-b fluorescence at the peak wavelength of 735nm. The fluorescence spectra can be received by our designed spectrometer with wavelength range of 400-780 nm and resolution of 2 nm. The chlorophyll-b in leaf can be obtained by analyzing the fluorescence intensity ratio F₇₃₅/ F₆₈₅. In experiment, we measured the spectra of chlorophyll-b in different epipremnum aureum leaves using our designed instrument at the distance of 5m., then calculated the corresponding fluorescence intensity ratio F₇₃₅/ F₆₈₅ of leaves, and established the correlation between chlorophyllb concentration measured by spectrophotometer and F₇₃₅/ F₆₈₅. The correlation coefficient value r² is 0.84. The experimental results prove that our designed portable non-contact chlorophyll measurement instrument has the advantages of high detection speed, high accuracy and simplicity, which can be widely used in real-time chlorophyllb detection of leaf.