Lie Lin

3D printed low-loss THz waveguide based on Kagome photonic crystal structure

A low-loss hollow core terahertz waveguide based on Kagome photonic crystal structure has been designed and fabricated by 3D printing. The 3D printed waveguide has been characterized by using THz time-domain spectroscopy. The results demonstrate that the obtained waveguide features average power propagation loss of 0.02 cm-1 for 0.2-1.0 THz (the minimum is about 0.002 cm-1 at 0.75 THz). More interesting, it could be simply mechanically spliced without any additional alignment, while maintaining the excellent performance. The 3D printing technique will be a promising solution to fabricate Kagome THz waveguide with well controllable characteristics and low cost.

Spectral discrimination between normal and leukemic human sera using delayed luminescence

In this work, photoinduced delayed luminescence (DL) was used to distinguish serum samples of patients with acute lymphoblastic leukemia from those of healthy volunteers. DL decay kinetics of human serum samples was measured using a homebuilt ultraweak luminescence detection system. It was found a significant difference in the weight distribution of the decay rate between normal and leukemic serum samples. A comparison of the DL kinetics parameters including the initial intensity, the peak decay rate, and the peak weight value was used in making discrimination between normal and leukemic human sera. Results in this work contribute to the development of a novel optical method for the early diagnosis of leukemia.

Further localization of optical field for flower-like silver particles under laser radiation

We find the surface optical field of submicron silver particles can be further localized by their surface roughening, which leads to a greatly enhanced local field. The flower-like silver particles were prepared and the extinction spectra were measured in our work. A high enhancement factor of 1.3 × 107 was obtained by surface-enhanced Raman spectrum. Besides that, the correlation between the surface plasmon resonance mode and surface local field was also studied by theoretical analysis. The results show the plasmon resonance modes of flower-like silver particles include dipole and multipole plasmon resonances. For the dipole plasmon resonance at long wavelength, the local field near polar regions will be further localized as a result of the rough surface. In contrast, the interaction of local field between surface structures will cause hotspots for the multipole plasmon resonance in the short-wave region. Based on these factors, we demonstrate that the rough-surface-induced field superposition results in the redistribution and enhancement of the optical field around the particles.

Tunable reflecting terahertz filter based on chirped metamaterial structure

Tunable reflecting terahertz bandstop filter based on chirped metamaterial structure is demonstrated by numerical simulation. In the metamaterial, the metal bars are concatenated to silicon bars with different lengths. By varying the conductivity of the silicon bars, the reflectivity, central frequency and bandwidth of the metamaterial could be tuned. Light illumination could be introduced to change the conductivity of the silicon bars. Numerical simulations also show that the chirped metamaterial structure is insensitive to the incident angle and polarization-dependent. The proposed chirped metamaterial structure can be operated as a tunable bandstop filter whose modulation depth, bandwidth, shape factor and center frequency can be controlled by light pumping.

Physical mechanism of delayed luminescence from human serum

The fluorescence spectra, delayed luminescence (DL) spectra and DL decay dynamics of human serum were studied by fluorescence and time resolved emission spectrum technology under different excitation conditions in this paper. The results we obtained are shown as follows: (1) the DL spectrum is similar to the time resolved fluorescence spectrum within 50ns after Ps laser pulse excitation. (2) The intensity and decay time of DL from the serum samples are dependent on excitation power and irradiation time. Under fixed excitation power, the longer irradiation time is, the higher the DL intensity; after the excitation energy reaches about 200mJ, the DL intensity is nearly unchanged. The change of DL decay time follows the similar regulation to that of DL intensity. (3) As the excitation energy increases, the spectral distribution of the relative intensities exhibits an observable change. The higher the excitation energy is, the stronger the relative intensity at short wavelength region. The results show that the delayed luminescence of human serum is mainly originated from its delayed fluorescence, phosphorescence, and induced bio-photon emission. These results may be also useful for the development of serum diagnosis technology.

Detecting Trace Amounts of Narcotics in Serum by Delayed Luminescence

This paper was designed to test the feasibility of optical identification of trace amounts of narcotics in serum using photoinduced delayed luminescence (DL). Comparative investigation of control serum and contaminated samples with methamphetamine and heroin was conducted. For the control serum without chemical contamination, the delayed photon emission decay shows an intrinsic lifetime of about 38.4 ms, whereas DL decay curves of the serum containing 1 × 10-5 mol/L of methamphetamine and 1 × 10-5 mol/L of heroin reveal shortened characteristic lifetimes of 19.3 and 24.6 ms, respectively. Experimental results demonstrate that the lifetime can be used as an indicator of containing narcotics in serum, promising a new method for detecting trace amounts of narcotics in serum.

DELAYED LUMINESCENCE AS AN OPTICAL INDICATOR OF TOBACCO LEAF QUALITY

In this paper, we present our study on the spectral discrimination between high and low quality tobacco leaves using a time-resolved ultraweak luminescence detection system. Photoinduced delayed luminescence (DL) is employed as a nondestructive and objective indicator of tobacco leaf quality. DL decay kinetics of tobacco leaf samples is measured, and the data are fitted by a hyperbolic cosecant function. Results show that the function’s parameter A is significantly related to the quality grades of tobacco leaves—compared with the low quality tobacco leaves, an increase of the A value by a factor of 7 is obtained for the high quality tobacco leaves. Research from this work contributes to the development of a novel optical method applicable for the quality evaluation of agricultural crops and food products.

In-situ visualization of multiple filament competition dynamic during nonlinear propagation of femtosecond laser

In this work, multiple filamentation competition of femtosecond pulse in methanol is studied both experimentally and numerically. The visualization of multiple filamentation competition has been realized in the experiment performing the three-photon fluorescence of Coumarin 440. The random changes of multiple filamentation stemmed from the jitter of the peak laser intensity ratio of initial hot spots are first observed directly and visually, which can be well explained by a simplified (2D+1)-dimensional model.

Photo-induced delayed luminescence of human serum and its dependence on excitation conditions

The photo-induced delayed luminescence (DL) of human serum and its dependence on exciting conditions, including exciting wavelength, exciting energy and exciting power, were studied in this paper. It was found that the DL of serum follows the law of hyperbolic decay rather than exponential decay, exhibiting coherent character. The exciting conditions had affinities with the activation as well as the active reactions of biological molecules, which were sensitive and active under UV-light excitation. Exciting energy mainly decides the activation. More sufficient activation leads to more drastic active reactions and stronger re-emission ability of bio-molecules after illumination, resulting in the more intensive photon emission and lower DL decay speed rate. On the other hand, exciting power also plays an important role in impacting the active reactions. Exciting light with higher power makes the active reactions more drastic, causing the higher photon counts. However, there are few correlations between exciting power and the re-emission ability of bio-molecules. These results may be useful for investigation and application of human serum.

Image fiber-based miniature multi-functional suspended solid sensor

An image fiber-based miniature suspended solid sensor has been demonstrated. The diameter of the sensor is only a few millimeters. A superhydrophobic material is coated on the end of the image fiber to avoid the adsorption of suspended solids and bubbles. Multiple parameters, including mass concentration, morphology and particle sizes of suspended solids, can be visually measured in real time. Dynamic ranges of 0 ~ 100 kg/m3, full range accuracies of ±2‰ and a response time of 0.05 s were experimentally realized for the mass concentration measurements. Determinations of particle sizes of the suspended solids are also presented by means of digital image processing. This new technique will significantly advance ultralow-intrusion measurements in studies on the dynamics of suspended solids.