Explanation of the concept of time resolved spectroscopy, definition of spectral resolution

HPS-LCF series 3D line spectral confocal sensor has a built-in high-efficiency AI image recognition algorithm, which can obtain the 3D imaging information of the whole surface part of the measured object by scanning it once, and has the characteristics of high detection accuracy, fast speed and good stability. Since the detection principle is based on white light dispersion, by using a special lens system, white light passes through the small hole to extend the focus halo range of different monochromatic lights, and then calculates the wavelength of the reflected light of the focus on the surface of the measured object, so that the precise distance data from the measured object to the lens can be obtained, which means that the measurement process will not be affected by the intensity of the reflected light, and almost any material can achieve high-precision detection. Spectral confocal method is a new detection technology, which is a supplement to the traditional laser detection method, or even an alternative, because it effectively solves the problem of transparent objects and high reflection in the industry

Time-resolved spectroscopy refers to a spectrum that observes transient processes in physics and chemistry and resolves their time. In the liquid phase, many physical and chemical processes, such as cis-trans isomerization and directional relaxation of molecules, transfer of charge and protons, pre-dissociation of excited molecule collisions, energy transfer and fluorescence lifetime, and solvation of electrons in water, can be completed in just 10 to 8 seconds. It is only after the picosecond laser pulses have been realized that it is possible to observe these extremely fast processes in a timely manner.

In 1966, the first mode-locked ND3+:YAG laser was used to obtain picosecond ultrashort light pulses. Acousto-optic modulated mode-locked dye lasers are now used to obtain light pulses of 10 to 11 seconds.

The time interval between pumping and probing laser pulses can be accurately controlled using an optical delay (10-9 sec 30 cm) or simultaneous pumping of two dye lasers.

In the gas phase, the energy transfer and reaction time between small molecules is mostly on the order of nanoseconds to milliseconds due to the weak intermolecular interaction, and the molecular energy transfer process can be studied by using an excimer laser and a dye laser with an output pulse width of 10 nanoseconds for pumping and detection.

Because the research process is extremely short, typically in the order of nanoseconds (1 nanosecond = 1 10 9 seconds) and even femtoseconds (1 femtosecond = 1 10 15 seconds), the excitation light source is required to be a tunable light source with short pulses or ultrashort pulses, and pulsed dye lasers and titanium-doped sapphire lasers are often used for temporal resolution spectroscopic research. The use of time-resolved spectroscopy to study the motion laws and interactions of microscopic particles has led to the discovery of many new phenomena and mechanisms. For example, the energy transfer between molecules, the internal transfer of electrons in molecules, the dynamic processes of chemical reactions, and the basic processes in photobiology are studied.

In spectroscopy, for continuous spectra, spectral resolution can be simply defined as the wavenumber δv (cm-1) or wavelength separation between two adjacent absorption features, as shown in Figure 5-4-1(a). To be precise, the two absorption features are required to have absorption values of the same magnitude and to be isolated by a minimum absorption valley (Mary Joan Blümich, 2002).

Figure 5-4-1 Definition of spectral resolution.

In a discontinuous band sensor, it is defined as the wavelength distance fwhm (in units) or wavenumber (cm-1) between the half-power points of the spectral response function on a certain wavelength band. Strictly speaking, the bandwidth of the band and the spectral resolution are two different concepts. Spectral resolution is not only related to the bandwidth of the band, but also to the spectral sampling interval.

According to the sampling theorem, at least two samples must be taken within the bandwidth range so as not to cause a loss of spectral high-frequency information. However, in practice, it usually refers to the number of bands of the sensor, the center wavelength position of each channel, and the band bandwidth, which together determine the spectral resolution (Zhao et al., 2003).

The lithology identification and mineral mapping of imaging spectral remote sensing mainly make use of the differences in the spectral characteristics of different rock and mineral types, mineral abundances and different components, especially the wavelength position, absorption depth and morphological characteristics of the spectral absorption band. The spectral resolution directly affects the detection and resolution of the spectral absorption bands and their morphological characteristics of rocks and minerals, which directly affects the ability to distinguish and identify mineral species and their compositions in the imaging spectral data.

Spectroscopic analysis: A method of identifying substances based on their spectrum.

1. Spatial oak search resolution.

A cell corresponds to a square on the ground, and the length of the side of the square is the spatial resolution.

2. Radiation resolution: it is color quantization and, a black and white image, the radiation resolution is like 2 and, and black, gray and white is 3 and.

3. Spectral resolution: There are many bands for remote sensing, and the band spacing is the spectral resolution.

4. The relationship between the three: it can be considered that there is no relationship, if you have to say the relationship between burning and leakage: if the spectral resolution is high, the spatial and radiometric resolution will be almost a little skin fibrillation.

The fringe camera method and pump detection method are commonly used to study the lifetime of the excited state of molecules. The former directly measures fluorescence lifetime, which is simple and easy to perform with high accuracy, but the system is more expensive. In the latter, the excited state lifetime of the molecule is obtained by measuring the time delay between the excitation light and the emitted light. Fluorescence spectroscopy is sometimes used to identify substances with very similar fluorescence spectra and is difficult to distinguish, so it is necessary to use time-resolved spectroscopy to identify.