We show wave breaking (WB) can occur in a dispersion decreasing fiber with normal group-velocity dispersion
preceding the parabolic pulse formation (PPF), and the distance where it happens can be described by two equations.
Based on the transformation of a nonlinear Schr dinger equation with the typical decreasing dispersion into the form of
the uniform dispersion and "equivalent" gain, the first equation is obtained to determine the virtual WB distance. The
corresponding real distance can then be acquired from the second equation derived from the fiber dispersion distribution
function. Both the analytical results are confirmed by the numerical simulations of the two forms NLSE, and illustrated
by the chirp oscillations appeared in the pulse edges, respectively. We further demonstrate that the spectral broadening of
the pulse is quite different from that of the pulse temporal evolution during the PPF process. In the initial stage, the
spectral broadening is dominated by the expansion of ripples in the central part of pulse caused by self-phase modulation
(SPM); while in the last stage, it is dominated by the widening of sidelobe in the pulse wings caused by four-wave
mixing (FWM). These facts reveal that FWM also plays an important role in the process of PPF besides SPM while the
WB point is the very threshold that FWM begins to take effect.
A new method for accurate measurement of content of textile mixture based on Fourier transform near infrared
spectroscopy is put forward. The near infrared spectra of 56 samples with different cotton and polyester contents were
obtained, in which 41 samples, 10 samples and 5 samples were used for the calibration set, validation set and prediction
set respectively. The wavelet transform (WT) was utilized for the spectra data compression. From the linear and
nonlinear perspective, multivariable linear regression (MLR) model based on the Lambert - Beer's law and back
propagation (BP) neural network model based on WT were developed. It indicates that the prediction accuracy of
WT-ca3-BP network model is 2% for calibration sample and 4% for validation sample, which is much higher than the
MLR model and is suitable for the prediction of unknown samples. On the basis of not changing the structure of the
WT-ca3-BP network model, calibration and validation samples were utilized fully to be re-set to new calibration samples,
which upgraded this model. The upgraded WT-ca3-BP network model was applied to predict unknown samples.
Experimental results show that this approach based on Fourier transform Near Infrared Spectroscopy can be used to
quantitative analysis for textile fiber.
A mass of reactive oxygen species(ROS) are produced in the process of smoking. Superfluous ROS can induce the
oxidative stress in organism, which will cause irreversible damage to cells. Fluorescent probe is taken as a marker of
oxidative stress in biology and has been applied to ROS detection in the field of biology and chemistry for high
sensitivity, high simplicity of data collection and high resolution. As one type of fluorescent probe, dihydrorhodamine
6G (dR6G) will be oxidized to the fluorescent rhodamine 6G, which could be used to detect ROS in mainstream
cigarette smoke. We investigated the action mechanism of ROS on dR6G, built up the standard curve of R6G
fluorescence intensity with its content, achieved the variation pattern of R6G fluorescence intensity with ROS content in
mainstream cigarette smoke and detected the contents of ROS from the 4 types of cigarettes purchased in market. The
result shows that the amount of ROS has close relationship with the types of tobacco and cigarette production
technology. Compared with other detecting methods such as electronic spin resonance(ESR), chromatography and mass
spectrometry, this detection method by the fluorescent probe has higher efficiency and sensitivity and will have wide
applications in the ROS detection field.
A new and non-invasive method adapted for optical diagnosis of early caries is proposed by researching on the
interaction mechanism of laser with dental tissue and relations of remitted light with optical properties of the tissue. This
method is based on simultaneous analyses of the following parameters: probing radiation, backscattering and
auto-fluorescence. Investigation was performed on 104 dental samples in vitro by using He-Ne laser (λ=632.8nm,
2.0±0.1mW) as the probing. Spectrums of all samples were obtained. Characteristic spectrums of dental caries in various
stages (intact, initial, moderate and deep) were given. Using the back-reflected light to normalize the intensity of
back-scattering and fluorescence, a quantitative diagnosis standard for different stages of caries is proposed. In order to
verify the test, comparison research was conducted among artificial caries, morphological damaged enamel, dental
calculus and intact tooth. Results show that variations in backscattering characteristic changes in bio-tissue
morphological and the quantity of auto-fluorescence is correlated with concentration of anaerobic microflora in hearth of
caries lesion. This method poses a high potential of diagnosing various stages of dental caries, and is more reliability to
detect early caries, surface damage of health enamel and dental calculus.
The effectiveness of Nd:YAG laser treatment on in vitro acid resistance of human enamel was studied. After surface
polishing, enamel blocks irradiated by different power laser and control group were put into 5ml of lactate buffer
solution (0.1mol/L), which was in water of 37°C for 72 hours. The hardness and morphology of enamel surface were
investigated by microhardness meter and scanning electron microscopy. Compared with control, the group with 0.3W
laser treatment has the least caries lesion (p<0.001). At the same time, the mechanism of caries prevention and acid
resistance by laser was discussed in detail. We drew a conclusion that the change of contents in enamel and crystal
orientations and partial decomposition of the organic matrix might be the main reason for enhancing acid resistance.
And best caries inhibition could be achieved when the temperature rising of enamel surface was in the range of
300~400°C by laser parameters being controlled suitably.
The aim is to study the effectiveness of continuous Nd:YAG laser inhibiting caries progression of human enamel. After surface polishing, enamel blocks irradiated by different power laser and control group were put into 5ml of lactate buffer solution (0.1mol/L), which was in water of 37°C for 72 hours. The microhardness and morphology of enamel surface were investigated by microhardness tester and scanning electron microscopy. Compared with control, the group with 0.3W laser treatment has the least caries lesion (p<0.001). At the same time, the mechanism of caries prevention and acid resistance by laser was discussed in detail. We drew a conclusion that the change of contents in enamel and crystal orientations and partial decomposition of the organic matrix might be the main reason for enhancing the acid resistance ability of enamel. And best caries inhibition could be achieved when the temperature rising of enamel surface was in the range of 300~400°C by laser parameters being controlled suitably.
Femtosecond laser is suitable to machine a variety of materials, such as metals, semiconductors, polymers, oxide ceramics, silica aerogels, optical glasses, crystals, deep sea sands and even explosives because of its high peak power density and low heat affected zone. In this paper, the femtosecond laser micromachining of different materials and for different processing is presented, including structuring in optical glasses, and the cutting of metals and the deep-sea (South China Sea) sands. The laser used in the experiment is a commercial Ti:Sapphire laser with the pulse width of 50 and 100 fs, wavelength of 800 nm, maximum pulse energy up to 2 mJ and the repetition rate of 1 kHz. The evolution of material eruption as a function of the number of laser pulses and intensity is studied. The dependence of ablation rate with laser intensity and the number of the pulses is characterized by measuring the maximum laser penetration depth in different materials.