Method For Time-resolved Measurements Research Articles

Observation of attosecond electron dynamics in the photoelectron momentum distribution of atoms using few-cycle laser pulses

The method of time-resolved measurement with ultrashort laser pulses is vital to the development of attosecond science. Pump-probe measurements using a train of attosecond pulses in combination with a near-infrared (NIR) multicycle driving laser have been successful in capturing the intercycle electron dynamics which repeats every optical cycle and leads to above-threshold ionization (ATI) spectra in the frequency domain. In this work, we study the effect of a carrier-envelope phase (CEP) in a few-cycle ($l6$ fs) NIR laser pulse on the photoelectron momentum distribution (PMD) of a hydrogen atom and show that interference patterns in a PMD change dramatically with CEPs in the few-cycle regime. When the few-cycle driving laser pulse has a sine shape, the double-slit interference with characteristic modulation of ATI peaks dominates the PMD. On the other hand, when the driving pulse has a cosine shape, the holographical interference featured by a spider-like pattern is isolated. Our results suggest that the CEP-stable few-cycle laser pulses can be used to identify different types of intracycle interference structures in a PMD which reveal the underlying subcycle electron dynamics on an attosecond timescale.

Study of laser-induced plant fluorescence lifetime imaging technology for plant remote sensing monitor

Plant fluorescence is too susceptible to interference and unsuitable for plant remote sensing monitor. A plant fluorescence lifetime imaging technology based on plant remote sensing monitor is presented to solve this problem. The technology can be used to analyse plant physiological information for environmental surveillance. The beam expander system was used to expand laser beam at a certain specific wavelengths, and the living plant chlorophyll fluorescence can be excited by this laser beam. Many of the same plant fluorescence signals were excited by continuous laser pulses, and furthermore the start delay time of Intensification Charge Coupled Device was adjusted consecutively in time resolved measurement method. Finally, a complete set of plant continuous fluorescence image was collected by Intensification Charge Coupled Device. The deconvolution can be used to retrieve the high-precision plant fluorescence lifetime of single pixel point in plant continuous fluorescence image. If the plant fluorescence lifetime values from all of pixel points were retrieved, the distribution map of plant fluorescence lifetime can be drawn. The fluorescence lifetime properties of living plants have already been studied preliminarily. The study indicates that the distribution map of plant fluorescence lifetime can more effectively reflect plant chlorophyll content than fluorescence intensity dose. The plant fluorescence lifetime was related to its chlorophyll content in a certain range, and there is a complex and subtle relationship between plant fluorescence lifetime and its physiological information.

Study of plant fluorescence properties based on laser-induced chlorophyll fluorescence lifetime imaging technology

Plant fluorescence is a susceptible signal in plant fluorescence remote sensing detection. In order to solve this problem, a technique for plant chlorophyll fluorescence lifetime imaging is presented to evaluate living status for plant growth and environmental monitoring. A concave lens is used to expand laser beam at a wavelength of 355 nm, and the living plant is exposed in this laser light source to excite chlorophyll fluorescence. And the chlorophyll fluorescence signals are detected by an intensification charge coupled device. Time resolved measurement method is used in this article, so that every time the same fluorescence signals can be excited by the same laser pulse. Meanwhile, the delay time needed for triggering intensification charge coupled device should be changed consecutively, and the whole discrete fluorescence signal can be obtained. The discrete fluorescence signals from the particular location points of the plant are fitted. An improved method of forward iterative deconvolution is used to retrieve the corresponding fluorescence lifetime, and the high-precision fluorescence lifetime can be obtained. Furthermore, the fluorescence lifetime values at all the location points are retrieved to obtain the distribution map of chlorophyll fluorescence lifetime. This method can give the chlorophyll fluorescence image efficiently. The distribution map of fluorescence lifetime can more effectively reflect the plant chlorophyll concentration than the fluorescence intensity image does. The physical property of chlorophyll fluorescence lifetime from living plants has been studied preliminarily, indicating that the plant physiological status is related to its fluorescence lifetime to a certain extent; and the chlorophyll fluorescence lifetime and plant environment have a subtle and complex correlation. In the future, the relationship between chlorophyll fluorescence lifetime and plant environment will be expected to study with the cooperation of biophysicist.

Laser-induced chlorophyll fluorescence lifetime measurement and characteristic analysis

A laser-induced fluorescence lifetime measurement method is presented to evaluate living status for plant growth and the environmental monitoring. A 355 nm laser is used as excitation source for exciting chlorophyll fluorescence, and the fluorescence signals are received by a photomultiplier. Because the measured signal is the convolution of the reliable fluorescence decay signals, laser pulse and instrument response function, according to their characteristics, the time-resolved measurement method is used to estimate the chlorophyll fluorescence and background signals separately; the real fluorescence decay signals are separated by combining a novel deconvolution method, and the chlorophyll fluorescence lifetime can be retrieved. Experiment shows that the method proves to be a high accuracy and real-time monitoring chlorophyll fluorescence lifetime technique; and the chlorophyll solution fluorescence lifetime is measured for different concentrations. The result can prove that the chlorophyll concentration is related to its fluorescence lifetime, and the calibration curves of chlorophyll concentration and fluorescence lifetime is fitted.

A new method for time-resolved measurements of plasma electron energy distributions

Abstract A method using difference quotient circuits is described for measuring the second derivative of a prove characteristic in time varying plasmas.