Fiber based frequency-modulated light scattering interferometry (FMLSI) is developed for optical properties studies of liquid phantoms, made of Intralipid®. By employing optical frequency modulation on a tunable diode laser, the power spectrum of the heterodyne-detected intensity fluctuations through the dynamic turbid medium is a combination of the time-of-flight distribution and the Doppler power spectrum due to the movement of the scattering particles. The reduced scattering coefficient, absorption coefficient and Brownian diffusion constant are retrieved by employing nonlinear fitting to the power spectrum based on diffusion theory.
A compact and low-cost light-emitting diode (LED) with center wavelength of 295 nm and high light density was used measure the concentration of sulfur dioxide, which has a strong structured absorption band in the ultraviolet region 300 nm. Differential optical absorption spectroscopy (DOAS) was used to determine the concentration of sulfur dioxide using reference absorption spectrum due to 1000 ppm SO<sub>2</sub>. A sensitivity of about 1.5 ppm was achieved with a gas cell in 1-s integration time, enabling real-time monitoring of sulfur dioxide.
Tobacco is one of the most important economic crops in the world, assessment of its quality has a very important business significance. A compact, low-cost, and maneuverable optical sensor system for classification evaluation of different tobaccos was described in this paper using light-emitting-diodes (LEDs)-induced fluorescence. The principal components analysis (PCA) method is used to extract the dominant features of the tobaccos for identifying the classification of tobaccos. The technique is suitable for practical identification due to the use of a straightforward data evaluation method and compact system.
The properties of micro-porous ceramics are studied in the present work using a tunable diode-laser-based setup. The relative optical porosity is retrieved by using gas in scattering media absorption spectroscopy (GASMAS) – which yields the path length travelled by photons through the gas-filled pores – and frequency domain photon migration (FDPM) – which evaluates the mean optical path length (MOPL) through the whole ceramic. The relationship between the relative optical porosity and the physical porosity is also studied.
Frequency-modulated light scattering interferometry, which employs a frequency-modulated coherent light source and
examines the intensity fluctuation of the resulting scattered light using a heterodyne detection scheme, was utilized to
evaluate the optical properties of liquid phantoms made of Intralipid® and Indian ink. Based on the diffusion theory,
nonlinear fits to the power spectrum of the heterodyne-detected light intensity are performed and discussed in detail, and
the optical properties of liquid phantoms are consequently retrieved.
Glyoxal (CHOCHO), as an indicator of photochemical “hot spots”, was for the first time the subject of a differential
absorption lidar (DIAL) campaign. The strongest absorption line of glyoxal in the blue wavelength region – 455.1 nm –
was chosen as the experimental absorption wavelength. In order to handle the effects of absorption cross-section
variation of the interfering gas – nitrogen dioxide (NO<sub>2</sub>) – three-wavelength DIAL measurements simultaneously detecting glyoxal and NO<sub>2</sub>, were performed. The differential absorption curves, recorded in July 2012, indicate an extremely low glyoxal concentration in Lund, Sweden, although it is expected to be peaking at this time of the year.
Laser-induced fluorescence (LIF) spectra of a bush and numerous branches of Chinese Longjing tea were investigated remotely with lidar techniques. The intensity ratio between the far red fluorescence (FRF) and red fluorescence (RF) due to the chlorophyll content of the tea branches were analyzed to study the growth conditions in different villages around Hangzhou, China. Dried Longjing tea leaves were also measured by LIF techniques in the laboratory. A chemometric method based on singular value decomposition (SVD) and linear discriminant analysis (LDA) was used to evaluate the tea qualities of the dried tea leaves.