A device for generating and detecting vortex of exciton-polariton condensate

Abstract

The present invention relates to an exciton-polariton condensate vortex generation and detection device. It mainly includes three parts: excitation light generation, exciton-polariton condensate vortex generation and signal acquisition terminal. The first part mainly includes a femtosecond laser and a continuous light laser, the second part mainly includes an excitation light path and an organic sample chamber, and the third part mainly includes an acquisition light path, a Michelson interference circuit and an image analysis terminal. First, the femtosecond laser generated by the femtosecond laser is converted into a femtosecond vortex beam, and the Gaussian light generated by the continuous light laser is converted into a flat-top light using a customized device; then, the femtosecond vortex light and the flat-top light are irradiated onto the sample surface together to excite the sample to generate exciton-polariton condensation; finally, the generation of the exciton-polariton condensate vortex is judged according to the result of the graph analysis terminal. The device has a simple structure and is easy to operate, and opens up a new way to generate and detect exciton-polariton condensate vortices.

Description

Technical Field

[0001] The present invention mainly relates to the fields of organic semiconductor microcavities, condensed matter, optoelectronics, and signal processing. In particular, it relates to technical methods such as the formation of Bose-Einstein condensate excitation, the generation of quantized vortices, the detection of spontaneous emission images, and the construction of Michelson interference circuits in organic semiconductor microcavities. Technical Background

[0002] Bose–Einstein condensate (BEC) is a gaseous condensed state proposed by Bose and Einstein in the 1920s of the last century. In 1995, Cornell, Wieman and their assistants successfully achieved a true BEC at the Joint Institute for Laboratory Astrophysics. In recent years, it has been found that the exciton-polariton system in organic semiconductor microcavities can achieve BEC at room temperature. This discovery has greatly stimulated people's enthusiasm for the research of exciton-polaritons in organic semiconductor microcavities. Its room-temperature superfluid properties exhibit great scientific research and application value, but the research on photon-exciton coupling in new organic semiconductors is still in its infancy. In organic semiconductors, the Rabi splitting of exciton-polaritons can reach hundreds of meV, so the tunable range of the emission wavelength of organic exciton-polaritons is also very large. Organic semiconductor exciton-polaritons with strong coupling, low cost, and tunable wavelength have important application prospects in Bose-Einstein condensation. In addition, due to the gyroscopic effect of exciton-polaritons, exciton-polaritons generated by the excitation of vortex light with orbital angular momentum also have great significance for the research of new gyroscopes. Summary of the Invention

[0003] The technical problem to be solved by the present invention is: Aiming at the problem that it is difficult to directly and simply prepare and detect exciton-polariton vortices in current organic semiconductor microcavities, the present invention aims to organically combine the preparation of vortex light with the excitation device of exciton-polaritons by designing an experimental optical path, and verify the generation of exciton-polariton vortex condensation through a spectrometer and a Michelson interference circuit.

[0004] The technical solution of the present invention is: The present invention relates to a device for generating and detecting exciton-polariton condensate vortices, as Figure 1As shown in the figure, its main components include: femtosecond laser (1), femtosecond laser controller (2), optical parametric amplifier (3), plane mirror 1 (4), plane mirror 2 (5), plane mirror 3 (6), beam splitter 1 (7), half-wave plate (8), beam splitter 2 (9), flipable plane mirror (10), microscope objective (11), sample chamber (12), beam splitter 3 (13), collimating lens 1 (14), plane mirror 4 (15), delay line (16), plane mirror 5 (17), beam splitter 4 (18), charge-coupled sensor camera 1 (19), spectrometer (20), image acquisition and processing terminal (21), notch filter (22), charge-coupled sensor camera 2 (23), beam splitter 5 (24), collimating lens 2 (25), short-pass filter (26), white light source (27), continuous-wave laser (28), flat-top light diffractive optical element (29), spatial light modulator (30). First, by using the white light source (27), the sample in the sample chamber (11) is adjusted to a suitable position in the field of view of the charge-coupled sensor camera 2 (23). Then the white light source (27) is turned off, and the femtosecond laser (1) is turned on to generate a femtosecond laser beam. Through the femtosecond laser controller (2), the femtosecond laser (1) and the optical parametric amplifier (3) are controlled to convert into a femtosecond laser beam with a set power and frequency. The beam passes through the plane mirror 1 (4), then through the plane mirror 2 (5), the spatial light modulator (30) and the plane mirror 3 (6) to form a femtosecond vortex beam; the continuous-wave laser (28) generates continuous Gaussian light, which is converted into continuous flat-top light by the flat-top light diffractive optical element (29). The femtosecond vortex beam and the continuous flat-top beam are combined into one beam after passing through the beam splitter 1 (7), and then pass through the half-wave plate (8) and the beam splitter 3 (13) and are irradiated on the organic sample chamber (12) through the microscope objective (11). At this time, spontaneous emission patterns will be generated on the sample surface. The radiation light patterns pass through the microscope objective (11) and the beam splitter 3 (13), and then sequentially pass through the collimating lens 1 (14), the filter (26) and the collimating lens 2 (25), and are divided into two beams after passing through the beam splitter 5 (24), and are respectively collected by the charge-coupled sensor camera 2 (23) and the spectrometer (20), and the data is transmitted to the image acquisition and processing terminal (21) for analysis and processing. By controlling the parameters of the laser control terminal (2), the power and frequency of the excitation light are adjusted in real time. When the power is lower than the threshold for generating Bose-Einstein condensation, only fluorescence phenomena are observed in the sample; when the power is further increased, lasing phenomena will occur in the sample, and obvious changes in light intensity are observed; when the power is continuously increased, the sample will be ablated and damaged.After controlling the generation of Bose-Einstein condensate, by controlling the flippable planar mirror (10), the radiation light passes through the beam splitter 4 (18). One path passes through the delay line (16) and the planar mirror 5 (17) and then recombines with the other path passing through the planar mirror 4 (15) at the beam splitter 4 (18) to generate shear interference. The interference pattern is sensed by the charge-coupled sensor camera 1 (19) and analyzed and processed by the image acquisition and processing terminal (21). This device not only generates vortex light and irradiates the sample through the optical path, but also can use the information of the image acquisition and processing terminal to observe the phenomenon excited by Bose-Einstein condensate in real time, and can make a real-time judgment on the generation of vortex condensate.

[0005] The principle of the present invention is:

[0006] (1) Generation of exciton-polaritons based on superfluid properties

[0007] Superfluidity is a quantum effect on a macroscopic scale. Due to Bose-Einstein condensation, atoms will form a close collective, and superfluidity is the specific manifestation of this phenomenon. The physics community has been researching superfluidity and quantum vortices for nearly a century, and the development of ultracold atomic condensation provides an ideal platform with high controllability for research in this field. P. Kapitza first observed the superfluid phenomenon of Bose liquids and won the Nobel Prize in Physics in 1978; L. Landau proposed the quantum theory of superfluids, explaining and predicting many important properties of superfluids and won the Nobel Prize in Physics in 1962; A. A. Abrikosov solved the Ginzburg–Landau equation and found that quantum vortices will follow the principle of the lowest energy and arrange into a periodic lattice structure; A. Leggett proposed a new quantum theory, revealing the mechanism of superfluidity of liquid helium-3 Fermi, and they shared the Nobel Prize in Physics in 2003.

[0008] Different from macroscopic objects, microscopic particles have an additional "internal" angular momentum - spin in addition to the momentum in coordinate space. Particles with half-integer spin are called fermions, such as electrons, quarks, and neutrinos, and their spin is 1 / 2. Particles with integer spin are called bosons, such as gluons, photons, gravitons, W and Z bosons, and their spin is 1. For fermions, due to the Pauli exclusion principle, only one particle is allowed to fill each state. For bosons, the filling number of particles in each state is not restricted. After the temperature drops to a specific value, more and more bosons are in the state with the lowest energy, that is, the state with zero momentum, and this phenomenon is Bose-Einstein condensation.

[0009] (2) Bose-Einstein condensation based on lower-branch exciton-polaritons

[0010] Exciton-polaritons are quasiparticles formed by the mutual coupling of an exciton field and a photon field. Since the exciton-photon coupling problem is quadratic, the Hamiltonian H of the diagonalized exciton-polaritons can be analytically obtained as follows:

[0011]

[0012] where is the reduced Planck constant, k represents the wave vector, ω X (k) and ω C (k) represent the dispersions of the exciton field and the photon field respectively, and the coupling between the exciton and the photon can be described by the element Ω R in the matrix, which is called the Rabi splitting.

[0013] The eigenvalues of this matrix are given by the following equation, that is:

[0014]

[0015] Obviously, from the above formula, we can obtain the two branches of the dispersion relation of the exciton-polaritons, that is:

[0016]

[0017] The ω UP (k) and ω LP (k) in the above formula represent the two branches of the dispersion relation of the upper branch and the lower branch of the exciton-polaritons respectively. The Bose-Einstein condensation of the exciton-polaritons refers to the condensation of the lower-branch exciton-polaritons, and the vortex superposition state of the exciton-polaritons is also formed by the lower-branch exciton-polaritons.

[0018] (3) Generation of vortex light based on a spatial light modulator

[0019] A spatial light modulator (SLM) can change the phase, amplitude, and polarization state of an incident light beam and is an optical modulation device. Its principle is to first use a computer to simulate the hologram of the target light beam, and then after performing a gray-scale transformation on the hologram, convert it into a voltage signal and load it onto a liquid crystal display. The external voltage will change the orientation of the liquid crystal molecules, thereby controlling the birefringence of the liquid crystal to achieve the phase modulation effect on the light wave. When the initial incident light enters the display, the output light is the target light beam. The phase adjustment angle of each pixel point on the surface of the spatial light modulator is proportional to the distance that the light beam passes through in the liquid crystal layer, and the adjustment angle of each liquid crystal molecule in the liquid crystal layer is equal to the product of the voltage of this pixel point and the distance. Therefore, the total phase modulation of each pixel point (x, y) can be expressed as:

[0020]

[0021] In the formula, the phase modulation parameter is Δφ x,y (V) = φ x,y (V) - φ x,y (0), which depends on the position of the pixel and its corresponding control voltage; is a constant representing the phase compensation of each pixel.

[0022] The working principle of the SLM is described below using a Gaussian beam as an example:

[0023] If the waist radius of a Gaussian beam is ω 0 , and when ω = ω 0 , the amplitude expression of the Gaussian beam is:

[0024]

[0025] In the formula, r 0 , θ 0 are the parameters in the polar coordinates of the beam. The amplitude expression of the holographic pattern loaded on the SLM liquid crystal screen can be denoted as:

[0026]

[0027] When the hologram obtained from the above formula is loaded onto the surface of the SLM, the gray value of each pixel in the picture will be converted into the voltage of the corresponding pixel on the spatial light modulator screen, thereby realizing the precise angle control of the liquid crystal molecules and further achieving the goal of adjusting the beam phase.

[0028] Main advantages of the present invention:

[0029] (1) The structure is simple, the positions of all components are fixed, and the variables are only the power and frequency of the femtosecond beam controlled by the laser control end, which is easy to control; by using a flippable plane mirror, the device can detect both exciton-polariton condensation and vortices in the condensate, reducing the complexity of the optical path and the influence of light intensity on the detection equipment.

[0030] (2) The device has a wide range of applications. It can be seen from the designed device that the wavelength of the femtosecond laser used in the experiment is adjustable, and it can be used with pump lights of various wavelengths to excite Bose-Einstein condensation and study the excitation thresholds of pump lights with different wavelengths.

[0031] (3) The device is flexible in generating vortex light. Different holograms can be replaced in the spatial light modulator to form vortex lights with different topological charge numbers, and then the formation of exciton-polariton condensation and the effect of vortex condensation generated by the excitation of vortex lights with different topological charge numbers can be realized. These vortices can be used for the development of quantum devices such as quantum gyroscopes. Description of the Drawings

[0032] Figure 1 Schematic diagram of the detection device;

[0033] Figure 2 Vortex light optical field intensity diagram;

[0034] Figure 3 Schematic diagram of the organic sample;

[0035] Figure 4 Schematic diagram of exciton-polariton lasing;

[0036] Figure 5 Schematic diagram of the lasing spectrum;

[0037] Figure 6 Schematic diagram of the interference pattern observed after the Michelson interference circuit. Specific implementation scheme

[0038] The present invention uses the spontaneous emission interference pattern formed by the coupling of vortex light and exciton-polaritons in a semiconductor microcavity as the measurement carrier, and the specific implementation steps are as follows:

[0039] First, by using a white light source (27), the sample in the sample chamber (11) is adjusted to a suitable position in the field of view of the charge-coupled sensor camera 2 (23). The white light source (27) is turned off, and a femtosecond laser (1) is turned on to generate a femtosecond laser beam. Through the femtosecond laser controller (2), the femtosecond laser (1) and the optical parametric amplifier (3) are controlled to convert into a femtosecond laser beam with a set power and frequency. After passing through the plane mirror 1 (4), the beam passes through the plane mirror 2 (5), the spatial light modulator (30) and the plane mirror 3 (6) and then becomes a femtosecond vortex beam; the continuous wave laser (28) generates continuous Gaussian light, which is converted into continuous flat-top light through the flat-top light diffractive optical element (29).

[0040] The generated femtosecond vortex beam and the continuous flat-top beam are combined into one beam through the beam splitter 1 (7), and then pass through the half-wave plate (8) and the beam splitter 3 (13) and are irradiated on the organic sample chamber (12) through the microscope objective (11). At this time, Bose-Einstein condensation of the organic semiconductor microcavity will be excited on the sample surface and radiated light will be emitted.

[0041] The radiation light pattern passes through the microscope objective (11) and the beam splitter 3 (13), and then sequentially passes through the collimating lens 1 (14), the filter (26) and the collimating lens 2 (25). After passing through the beam splitter 5 (24), it is divided into two beams, which are respectively collected by the charge-coupled sensor camera 2 (23) and the spectrometer (20), and the data is transmitted to the image acquisition and processing terminal (21) for analysis and processing. The image obtained by the charge-coupled sensor camera 2 is as Figure 4 shown, and the generation of the lasing region can be clearly seen; the image obtained by the spectrometer is as Figure 5As shown, the emergence of lasing was observed near 490 nm, thus verifying the generation of exciton-polariton condensation.

[0042] In addition, after controlling the generation of Bose-Einstein condensation, by controlling the flippable plane mirror (10), the radiated light passes through the beam splitter 4 (18). One path passes through the delay line (16) and the plane mirror 5 (17) and then recombines with the other path passing through the plane mirror 4 (15) at the beam splitter 4 (18) to generate shear interference. The interference pattern is sensed by the charge-coupled sensor camera 1 (19) and analyzed and processed by the image acquisition and processing terminal (21). The image obtained by the charge-coupled sensor camera 1 is as Figure 6 shown. It can be judged from the bifurcation of the interference fringes in the figure that vortices appear in the generated exciton-polariton condensation.

[0043] The content not described in detail in this invention book belongs to the prior art well-known to those skilled in the art.

Claims

1. An exciton-polariton condensate vortex generation and detection device, comprising: Femtosecond laser (1), femtosecond laser controller (2), optical parametric amplifier (3), plane mirror 1 (4), plane mirror 2 (5), plane mirror 3 (6), beam splitter 1 (7), half-wave plate (8), beam splitter 2 (9), flip-over plane mirror (10), microscope objective (11), sample chamber (12), beam splitter 3 (13), collimating lens 1 (14), plane mirror 4 (15), delay line (16), plane mirror 5 (17), beam splitter 4 (18), charge coupled sensor camera 1 (19), spectrometer (20), image acquisition and processing terminal (21), notch plate (22) , a charge coupled sensor camera 2 (23), a beam splitter 5 (24), a collimating lens 2 (25), a short wave pass filter (26), a white light source (27), a continuous light laser (28), a flat top light diffraction optical device (29), and a spatial light modulator (30). First, by using the white light source (27), the sample in the sample bin (11) is adjusted to a suitable position in the field of view of the charge coupled sensor camera 2 (23), the white light source (27) is turned off, and the femtosecond laser (1) is turned on to generate a femtosecond laser beam, and the femtosecond laser controller (2) is used to control the femtosecond laser (1) and the optical parametric amplifier (3) to convert the power into the set value. A femtosecond laser beam of a certain frequency, the beam passes through a plane reflector 1 (4), a plane reflector 2 (5), a spatial light modulator (30) and a plane reflector 3 (6), and then becomes a femtosecond vortex beam; a continuous light laser (28) generates continuous Gaussian light, which is converted into a continuous flat-top light by a flat-top light diffraction optical device (29); the femtosecond vortex beam and the continuous flat-top beam are combined into one beam after passing through a beam splitter 1 (7), and then pass through a half-wave plate (8) and a beam splitter 3 (13), and then irradiate an organic sample chamber (12) through a microscope objective lens (11), and a spontaneous radiation pattern is generated on the sample surface; the radiation light pattern passes through the microscope objective lens (11) and the beam splitter 3 (13), and then successively passes through the collimating lens 1 (14), the filter (26) and the collimating lens 2 (25), and is divided into two beams by the beam splitter 5 (24), which are respectively collected by the charge coupled sensor camera 2 (23) and the spectrometer (20) and the data are transmitted to the image acquisition and processing terminal (21) for analysis and processing; the power and frequency of the excitation light are adjusted in real time by controlling the parameters of the laser control end (2). When the power is lower than the threshold value for generating Bose-Einstein condensation, only fluorescence phenomenon is observed in the sample; when the power is further increased, the sample will produce lasing phenomenon, and obvious changes in light intensity are observed; and when the power continues to increase, the sample will be ablated and damaged;After the Bose-Einstein condensation is controlled, the flip-able plane reflector (10) is controlled so that the radiation light passes through the beam splitter 4 (18), the delay line (16) and the plane reflector 5 (17), and then the light beam passes through the plane reflector 4 (15) and overlaps again at the beam splitter 4 (18) to generate shear interference. The interference pattern is sensed by the charge coupled sensor camera 1 (19) and analyzed and processed by the image acquisition and processing terminal (21).

2. A device for generating and detecting vortex of exciton-polariton condensate according to claim 1, characterized in that A femtosecond laser is used to generate a beam of femtosecond pulse light. The femtosecond laser adjusted by an optical parametric amplifier and a modulated flat-top light are irradiated onto the surface of an organic sample material through a specific optical path, so that the sample is stimulated to emit spontaneous radiation. The power and frequency of the emitted femtosecond laser are changed by changing the control coefficient of the laser control end, so that the femtosecond laser of specified power and frequency is irradiated onto the surface of the sample to generate stimulated radiation. The radiated light passes through a flip-up plane reflector. When the plane mirror is lowered, one beam of the radiated light is collected by a charge-coupled sensor camera after passing through a spectrometer, and the other beam is collected by a spectrometer. The collected signals are analyzed and processed in real time by an image acquisition and processing terminal, and combined with the spectrometer, it is determined in real time whether the sample is stimulated to radiate and generate Bose-Einstein condensation. When the plane mirror is raised, the radiated light is introduced into a Michelson interference circuit to detect interference fringes. If bifurcation occurs in the interference fringes, it proves that vortex condensation has occurred in the Bose-Einstein condensate.

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