阅读说明：本技术 一种分子泛频振转态激发制备分子束方法 (Method for preparing molecular beam by excitation of molecule broad-band vibration-inversion state ) 是由 陈震 陈志超 杨家岳 吴国荣 肖春雷 张未卿 杨学明 于 2019-01-07 设计创作，主要内容包括：一种分子泛频振转态激发制备分子束方法,包括以下步骤:分子红外光泛频激发的吸收截面较之基频小两个数量级以上；自行搭建一套有种子注入的的光参量放大器；种子注入极大减小激光的光谱宽度,稳定激光中心波长,提高激光能量输出稳定性；自行搭建了基于二极管和光栅分光的种子激光,获得光谱宽度为1MHz的稳定种子源,为窄线宽光参量放大器提供核心保障；利用自行搭建单纵模超窄线宽激光器实现了甲烷分子泛频振动转动量子态高效激发,并且有转动量子态的激发能力。本发明的优点：单纵模激光器与分子束技术结合,实现了分子泛频振转量子激发态的高效制备；通过交叉分子束离子速度成像技术实际测量了激发效率。(A method for preparing molecular beam by molecular overtone vibration-inversion excitation comprises reducing absorption cross section of molecular infrared overtone excitation by more than two orders of magnitude compared with fundamental frequency; a set of optical parametric amplifier with seed injection is built by self; the seed injection greatly reduces the spectral width of the laser, stabilizes the central wavelength of the laser and improves the energy output stability of the laser; seed laser based on diode and grating light splitting is built by self to obtain a stable seed source with the spectral width of 1MHz, and core guarantee is provided for a narrow-linewidth optical parametric amplifier; the single longitudinal mode ultra-narrow linewidth laser is automatically built, so that the methane molecule broad-band vibration rotation quantum state is efficiently excited, and the excitation capability of the rotation quantum state is realized. The invention has the advantages that: the single longitudinal mode laser is combined with the molecular beam technology, so that the efficient preparation of the molecular broad-band vibration-conversion quantum excited state is realized; the excitation efficiency was actually measured by cross-molecular beam ion velocity imaging technique.)

1. A method for preparing molecular beams by excitation of a flooding frequency oscillation state of molecules is characterized by comprising the following steps: the method for preparing the molecular beam by the excitation of the overtone vibration-inversion state of the molecule comprises the following steps:

first, infrared exciting light

The absorption cross section of the molecule infrared light spread-frequency excitation is smaller than the fundamental frequency by more than two orders of magnitude; the line width of the commercial laser can be considered as 1500MHz, and the output is unstable and is far greater than the wide-frequency absorption spectrum width of 150 MHz; this means that the fundamental frequency of the scheme with the same spectral line width as the commercial laser needs 5mJ, and the energy requirement of the broad-band excitation needs more than 500 mJ; this is far greater than its 12mJ design index, and no infrared laser with such parameter index is available in the world;

optimizing a universal frequency excitation scheme from the perspective of effective energy, and automatically building a set of optical parametric amplifier with seed injection; the seed injection greatly reduces the spectral width of the laser, stabilizes the central wavelength of the laser and improves the energy output stability of the laser; seed laser based on diode and grating light splitting is built by self to obtain a stable seed source with the spectral width of 1MHz, and core guarantee is provided for a narrow-linewidth optical parametric amplifier;

the optical parametric amplifier consists of OPO and OPA; the resonant cavity is an OPO annular cavity structure, so that no reflected light returns to the pump laser and the seed light laser; it consists of a four-sided custom mirror, as shown in fig. 1, where outcoupler functions to direct seed light into the cavity and the resulting Signal light and idler light out of the cavity; the cavity mirror at the upper left corner is fixed on a piezoelectric ceramic module, PZT, Piezomechanik GmbH, model HPSt 150/20-15/12 VS35 can move back and forth within the range of 0-12um, so as to finely adjust the longitudinal mode of the optical cavity; the lower left corner cavity mirror is used for introducing pump light; the upper right-corner cavity mirror is used for leading the pump light and the idler light out of the resonant cavity;

under the configuration of the resonant cavity, 532nm pump light only passes through two nonlinear crystals once and cannot start to vibrate in the cavity; the idler light generated from one nonlinear crystal is led out of the resonant cavity before entering the other nonlinear crystal, so that the inverse conversion of the signal light and the idler light to pump light is avoided; resonant cavities are very sensitive to vibrations; therefore, some additional measures are required; firstly, the four cavity mirrors are all arranged on a thicker aluminum plate, the height of the cavity mirrors relative to the aluminum plate is reduced as much as possible, and the influence caused by vibration of the base is reduced; secondly, a cover is made to cover the resonant cavity, so that the influence caused by air flow and sound vibration is remarkably reduced; light coming out of OPO firstly passes through a dichroic mirror to separate signal light from idler light, and then the needed idler light passes through another dichroic mirror again and is combined with 1064nm pump light and then passes through three KTP nonlinear crystals together; the energy of the idler light is further amplified to 8-30mJ in the OPA part; finally, laser output with the line width of 150MHz is realized;

two, molecular beam technical solution

The number of molecules to be excited in the laser field is another important index for preparing the broad-band excitation molecular beam, a commercial Even-L avie molecular beam pulse valve is excellent experimental equipment, and can obtain very high molecular number density;

the self-built single longitudinal mode ultra-narrow linewidth laser is utilized to realize the high-efficiency excitation of the methane molecule broad-band vibration rotation quantum state and has the excitation capability of the rotation quantum state; stable central wavelength, and long-term and high-efficiency preparation conditions.

Technical Field

The invention relates to an elementary collision reaction kinetic experiment technology of molecular quantum state resolution level, which is used for researching chemical processes such as molecular chemical bond breakage and formation and the like in the fields of energy-related combustion chemistry, environment-related atmospheric chemistry, space environment-related interplanetary chemistry and the like, in particular to a method for preparing a molecular beam by molecular broad-frequency vibration-transformation state excitation.

Background

The fields of energy, environment, space environment and the like are closely related to the survival and development of human beings. These fields are inseparable from chemical reactions. Chemical reactions are the generation of new substances, in which the formation and cleavage of chemical bonds are the most central processes. The molecular quantum state resolution level element collision reaction kinetic experiment research technology is an important method for researching chemical bond forming and breaking mechanism.

The high-pressure gas is adiabatically expanded to the low-temperature supersonic molecular beam flow with high strength and high directivity generated in the vacuum cavity through the small hole. During the expansion, violent collisions between molecules occur. The heat energy of random movement is converted into the kinetic energy of molecular directional movement, so that the translation temperature is sharply reduced. The cooling effect of the vibrations, rotations, etc. within the molecule is then related to the coupling between the translational degrees of freedom of the molecule. The rotational-translational relaxation efficiency is generally relatively high, so cooling of the rotation is very significant. This makes it possible to prepare single-rotating-state-populated, high-population-density reactants, with a tremendous push to spectroscopic, photolytic, and collision reaction state-to-state resolution experiments.

The cross molecular beam experiment is to make two molecular beams collide and scatter to trigger chemical reaction, and to detect the quantum state and angular distribution of the product to estimate the chemical reaction process. In the cross molecular beam scattering experiment, the initial conditions of the reaction are determined, and the state after scattering can be clearly measured, so the cross molecular beam scattering experiment is an experimental method for quantitatively researching the chemical reaction and can provide the most detailed information of the collision process of the molecular reaction. In the cross-molecular beam experiment, the reactant molecules only undergo a single collision in the cross region, which provides a necessary basis for quantitative experiments: the reactant molecules participate in collisions in a defined state (velocity, direction, quantum state, etc.); the product molecules will remain at the end of the collision until detected by the detector, and kinetic information of the collision can be obtained by measuring the scatter angle distribution and energy distribution of the reactant molecules.

The ion velocity imaging method is an ideal experimental method for simultaneously detecting the velocity distribution and the full-dimensional angular distribution of particles, and is the most important universal detection means for the cross molecular beam collision reaction. It measures the time of flight of the particles within a certain distance using a method similar to the time of flight spectroscopy (TOF) method, and the distance the particles fly within a certain time using an ion velocity imaging method. In the experiment, the dissociated fragments generated by photolysis of the parent molecule were first subjected to state-selective ionization by the REMPI method. Fragment ions generated at different spatial locations with the same velocity vector are accelerated by a precisely confined electric field and fly towards and "focus" on a position sensitive detector (MCP + PS + CCD), producing a two-dimensional image of ions with mass and internal quantum state resolution. The method eliminates the influence of ion source space distribution and greatly improves the spatial resolution of the ion velocity image.

It is believed that molecules in the excited state are more reactive than molecules in the ground state. This is because the molecules in the excited state have more internal energy that helps them to jump the energy barrier, thereby increasing the reaction rate. However, there are many forms of intramolecular excitation, including excitation of electronic states, excitation of vibrational states, and excitation of rotational states. Different forms of excitation, on the one hand, vary in the amount of energy and, on the other hand, vary in the manner and degree of coupling to the reaction path, and therefore have different effects on the chemical reaction. It is of great significance to experimentally study the reaction properties of molecules in different excited states. Firstly, the method is helpful for deepening the essential understanding of the chemical reaction and promoting the development of a relevant theoretical model; second, by controlling the excitation pattern of the reactant molecules, it is possible to achieve quantum state regulation of chemical reactions. In many important combustion, atmospheric, interplanetary chemical reaction processes, vibration-excited reactant molecules are widely present and play an important role, having practical significance for human production and life. From the perspective of molecular reaction kinetics, how does the initial vibrational excitation of the reactant molecules evolve into the internal coordinates of the product molecules and affect reaction rates and energy partitioning? Therefore, the question of how molecular vibrations affect chemical reactions has been of particular interest.

Molecules with infrared activity in the infrared band, mainly near infrared (0.8-2.5um) and mid-infrared (2.5-25um), have strong absorption peaks closely related to the molecular structure, corresponding to specific vibrational transition states on the basis electron state, absorbing an infrared photon of appropriate wavelength, the molecule will be pumped from the ground state to the vibrational excited state, a method widely used for preparing vibrational-excited reactant molecules, suitable for vibrational modes with infrared activity, with the major drawbacks of (1) the past, since the main tunable light source in the laboratory was a dye laser, whereas the tuning range of the dye laser was ultraviolet to near infrared, difficult to extend to the region with a wavelength greater than 1um, thus limiting the use of this method, although for nearly decades, the rapid development of laser technology and the emergence of new nonlinear crystal materials, parametric oscillators, or using coherent difference-frequency technology to generate strong infrared radiation, already become the usual nbs in the laboratory, but the stronger infrared energy generation still less than the normal, even though the coherent difference-frequency technology involves less absorption of infrared photons (3. sub.2. sub.4. sub.2. sub.3. mu. m. the absorption of infrared energy, thus, including the absorption of infrared spectrum, the absorption of the absorption spectrum of the laser, including the absorption of photons, and the absorption of.

Disclosure of Invention

The invention aims to realize the efficient preparation of a molecular broad-band vibration-inversion quantum excitation state, actually measures the excitation efficiency through a cross molecular beam ion velocity imaging technology, and particularly provides a method for preparing a molecular beam by molecular broad-band vibration-inversion state excitation.

The invention provides a method for preparing molecular beams by excitation of a molecule broad-band vibration-transition state, which is characterized by comprising the following steps: the method for preparing the molecular beam by the excitation of the overtone vibration-inversion state of the molecule comprises the following steps:

first, infrared exciting light

The absorption cross section of the molecule infrared light broad-band excitation is more than two orders of magnitude smaller than the fundamental frequency. The linewidth of the commercial laser can be considered as 1500MHz and the output is unstable, much larger than the broad absorption spectral width 150 MHz. This means that a scheme with the same spectral linewidth as a commercial laser requires 5mJ at the fundamental frequency and more than 500mJ for overtone excitation. This is much greater than its 12mJ design specification and infrared lasers are not available worldwide for such parameter specifications.

Optimizing a universal frequency excitation scheme from the perspective of effective energy, and automatically building a set of optical parametric amplifier with seed injection; the seed injection greatly reduces the spectral width of the laser, stabilizes the central wavelength of the laser and improves the output stability of the laser energy. Seed laser based on diode and grating light splitting is built by self, a stable seed source with the spectral width of 1MHz is obtained, and core guarantee is provided for the narrow-linewidth optical parametric amplifier.

The optical parametric amplifier consists of OPO and OPA; the resonant cavity is an OPO ring cavity structure, which ensures that no reflected light returns to the pump laser and the seed laser. It consists of a four-sided custom mirror, as shown in fig. 1, where outcoupler functions to direct seed light into the cavity and the resulting Signal light and idler light out of the cavity. The cavity mirror at the upper left corner is fixed on a piezoelectric ceramic module, PZT, Piezomechanik GmbH, model HPSt 150/20-15/12 VS35 can move back and forth within the range of 0-12um, so that the longitudinal mode of the optical cavity can be finely adjusted. The lower left corner cavity mirror is used for introducing pump light. The upper right-hand cavity mirror is used for leading the pump light and the idler light out of the resonant cavity.

Under the configuration of the resonant cavity, 532nm pump light only passes through two nonlinear crystals once and cannot start to vibrate in the cavity; the idler light generated from one nonlinear crystal is led out of the resonant cavity before entering another nonlinear crystal, so that the inverse conversion of the signal light and the idler light to the pump light is avoided. The resonant cavity is very sensitive to vibrations. Therefore, some additional measures are required. Firstly, the four cavity mirrors are all arranged on a thicker aluminum plate, the height of the cavity mirrors relative to the aluminum plate is reduced as much as possible, and the influence caused by vibration of the base is reduced; and secondly, a cover is made to cover the resonant cavity, so that the influence caused by air flow and sound vibration is remarkably reduced. Light coming out of OPO firstly passes through a dichroic mirror to separate signal light from idler light, and then required idler light passes through another dichroic mirror again and is combined with 1064nm pump light and then passes through three KTP nonlinear crystals together. The energy of the idler light is further amplified to 8-30mJ in the OPA section. Finally, the laser output with the line width of 150MHz is realized.

Two, molecular beam technical solution

The number of molecules to be excited in a laser field is another important index for preparing a broad-band excitation molecular beam, a commercial Even-L avie molecular beam pulse valve is excellent experimental equipment, and very high molecular number density can be obtained.

The self-built single longitudinal mode ultra-narrow linewidth laser is utilized to realize the high-efficiency excitation of the methane molecule broad-band vibration rotation quantum state and has the excitation capability of the rotation quantum state; stable central wavelength, and long-term and high-efficiency preparation conditions.

The invention has the advantages that:

according to the method for preparing the molecular beam by the excitation of the broad-band oscillation-transition state of the molecule, the single longitudinal mode laser built by self is combined with the molecular beam technology, so that the efficient preparation of the broad-band oscillation-transition quantum excitation state of the molecule is realized; the excitation efficiency was actually measured by cross-molecular beam ion velocity imaging technique.

The capability of experiment and research of the broad-band vibration excited molecular element collision reaction kinetics is developed. A new opportunity is opened for the research of the civil important fields of atmospheric chemistry, interplanetary chemistry, particularly combustion chemistry and the like.

Drawings

The invention is described in further detail below with reference to the following figures and embodiments:

FIG. 1 is a schematic diagram of an OPO resonant cavity;

FIG. 2 is a schematic diagram of a molecular beam fabrication method with molecular vibrational conversion into quantum states;

FIG. 3 is a schematic diagram of an experimental apparatus for cross molecular beam ion velocity imaging;

FIG. 4 shows the experimental results of the methane molecule overtemperature vibration-conversion quantum state excitation example;

FIG. 5 shows the long-term monitoring of the wavelength of the excitation light.

Detailed Description