Zuguang Guan

Insect monitoring with fluorescence lidar techniques: feasibility study

We investigate the possibilities of light detection and ranging (lidar) techniques to study migration of the damselfly species Calopteryx splendens and C. virgo. Laboratory and testing-range measurements at a distance of 60 m were performed using dried, mounted damselfly specimens. Laboratory measurements, including color photography in polarized light and spectroscopy of reflectance and induced fluorescence, reveal that damselflies exhibit reflectance and fluorescence properties that are closely tied to the generation of structural color. Lidar studies on C. splendens of both genders show that gender can be remotely determined, especially for specimens that were marked with Coumarin 102 and Rhodamine 6G dyes. The results obtained in this study will be useful for future field experiments, and provide guidelines for studying damselflies in their natural habitat using lidar to survey the air above the river surface. The findings will be applicable for many other insect species and should, therefore, bring new insights into migration and movement patterns of insects in general.

Insect monitoring with fluorescence lidar techniques: field experiments.

Results from field experiments using a fluorescence lidar system to monitor movements of insects are reported. Measurements over a river surface were made at distances between 100 and 300 m, detecting, in particular, damselflies entering the 355 nm pulsed laser beam. The lidar system recorded the depolarized elastic backscattering and two broad bands of laser-induced fluorescence, with the separation wavelength at 500 nm. Captured species, dusted with characteristic fluorescent dye powders, could be followed spatially and temporally after release. Implications for ecological research are discussed.

Clinical system for non-invasive in situ monitoring of gases in the human paranasal sinuses

We present a portable system for non-invasive, simultaneous sensing of molecular oxygen (O(2)) and water vapor (H(2)O) in the human paranasal cavities. The system is based on high-resolution tunable diode laser spectroscopy (TDLAS) and digital wavelength modulation spectroscopy (dWMS). Since optical interference and non-ideal tuning of the diode lasers render signal processing complex, we focus on Fourier analysis of dWMS signals and procedures for removal of background signals. Clinical data are presented, and exhibit a significant improvement in signal-to-noise with respect to earlier work. The in situ detection limit, in terms of absorption fraction, is about 5x10(-5) for oxygen and 5x10(-4) for water vapor, but varies between patients due to differences in light attenuation. In addition, we discuss the use of water vapor as a reference in quantification of in situ oxygen concentration in detail. In particular, light propagation aspects are investigated by employing photon time-of-flight spectroscopy.

Broad-band multispectral microscope for imaging transmission spectroscopy employing an array of light-emitting diodes

Optical spectral analysis and multispectral imaging provide powerful means for characterizing samples in a wide variety of applications and on many spatial scales. We present a simple implementation of these techniques in the context of microscopy. A modified commercial microscope equipped with a CMOS imaging detector, combined with an array of light emitting diodes with emission ranging from ultraviolet to near-infrared wavelengths, is described, and examples of information enhancement using multivariate analysis are presented.

Assessment of photon migration in scattering media using heterodyning techniques with a frequency modulated diode laser

A novel technique for studying photon propagation in scattering media is proposed and demonstrated, as is believed, for the first time. Photons propagating through the medium, from a frequency-ramped single-mode diode laser, meet a reference beam from the same source, at a common detector, and beat frequencies corresponding to various temporal delays are observed by heterodyne techniques. Fourier transformation directly yields the temporal dispersion curve. Proof-of-principle experiments on polystyrene foam and a tissue phantom suggest, that the new method, when fully developed, may favorably compete with the more complex time-correlated single-photon counting (TCSPC) and the phase-shift methods, now much employed.

Quasi zero-background tunable diode laser absorption spectroscopy employing a balanced Michelson interferometer.

Tunable diode laser spectroscopy (TDLS) normally observes small fractional absorptive reductions in the light flux. We show, that instead a signal increase on a zero background can be obtained. A Michelson interferometer, which is initially balanced out in destructive interference, is perturbed by gas absorption in one of its arms. Both theoretical analysis and experimental demonstration show that the proposed zero-background TDLS can improve the achievable signal-to-noise ratio.

Active feedback regulation of a Michelson interferometer to achieve zero-background absorption measurements

An active phase-controlling scheme based on a proportional-integral-derivative-controlled piezoelectric transducer is presented with the purpose of stabilizing a quasi-zero-background absorption spectrometer. A fiber-based balanced Michelson interferometer is used, and absorption due to a gas sample in one of its arms results in an increased light signal to a detector, which otherwise, thanks to destructive interference, experiences a very low light level. With the presented approach, the sensitivity of already potent absorption measurement techniques, e.g., based on modulation, could be improved even further.

Laser-induced fluorescence monitoring of Chinese longjing tea

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.

Zero-background tunable diode laser absorption spectroscopies using balanced interferometers

Tunable diode laser spectroscopy (TDLS) is one of the most successful techniques for trace-gas environmental monitoring [1–3]. By modulating the light source at high frequency for suppressing the noise [2], frequency modulation or wavelength modulation TDLS can measure optical absorption in atomic or molecular samples with high resolution and sensitivity. Apart from these absorptive techniques, there exists a group of zero-background spectroscopic methods [3], e.g. laser-induced fluorescence spectroscopy, photo-acoustic spectroscopy, and polarization spectroscopy. Here a spectroscopic signal rises from a zero or low background with little noise and these methods therefore can achieve good signal-to-noise ratio (SNR) even without any modulation on the light source.

LIDAR techniques for studying insect migration and distributions

LIDAR techniques have been extensively used for studies of aerosol particles. Fluorescence LIDAR was employed for studying natural bio aerosols, such as pollen, but also possible warfare agents [1]. Insects, being “large aerosol” particles clearly give rise to LIDAR returns. Recently, honey bees were studied by polarization reflectance LIDAR and their superior olfactory abilities were used in attempts to detect landmines [2]. Together with coworkers at the section for Animal Ecology, Lund University, we have initiated a project for using LIDAR, and in particular its fluorescence variety, to study the migration and distribution of two species of damselflies of special interest (Caloptoryx virgo and C. splendens). LIDAR techniques may be an interesting possibility to study the behavior and migration of insects, of relevance to ecology, agriculture and evolution [3]. This is especially true since known tracing techniques like GPS and RFID are unsuitable for insects, because of size and weight. The absorption of most insects is primarily explained by melanin and ommochromes, whereas the structural colors are considerably more characteristic for the species and genders, and are ideal for insect classification [4–7]. While the RADAR community for a long time has been exploring the opportunities for accessing structural interference “colors” [8], given by matched illumination, the LIDAR community mostly focused on chemical colors, using e.g. DIAL, LIF, LIBS [9]. We here report on spectroscopic results obtained in the laboratory and in short-range (60 m) LIDAR measurements on mounted, dried damselflies specimens, in attempts to classify genders and species. Elastic scattering as well as auto fluorescence and marker die fluorescence studies were performed. Laboratory work demonstrates imprints of structural color in the auto fluorescence spectra (Fig. 1). Possibilities for upcoming in vivo measurements during a summer field campaign are discussed.