Intensity clamping during dual-beam interference

One has prospected to overcome the intensity clamping phenomenon during femtosecond laser filamentation by superimposing two beams. This experimental scheme is thus studied in our work. We have realized the interference of two ultrashort laser beams and one of them creates a filament in air. The formation of a dynamic plasma grating induced by the interference pattern is observed. However, qualitative analysis of the experimental results indicates that intensity clamping still governs the intensity evolution during the dual-beam interaction. The expectation of greatly increasing laser intensity by dual beams superposition might not be realistic.     

Coherent field emission from a multi-walled carbon nanotube with two open-ended branches

Interference fringes are obtained in a field-emission microscopy (FEM) study of a multi-walled carbon nanotube (MWCNT) with two open-ended branches. The FEM pattern, which is composed of three parallel streaks, can be interpreted by using classical Young's double-slit interference with the ends of the two MWCNT branches treated as two secondary sources of the electron wave. The origin of the coherency of the electron beams from the two branches is discussed on the basis of the quantitative analysis of the FEM pattern. The result suggests a new approach to obtaining a coherent electron source.     

Change of interference pattern using fundamental and second-harmonic wavelengths by phase shift of a beam

Interference pattern of two different wavelengths, forming a four-sided pyramid consisting of eight beams, is discussed. Synchronization between two wavelengths having a multiple relationship, which corresponds to mixing of fundamental and second-harmonic generation wavelengths, forms a stationary interference pattern successfully. Phase shift variation of a beam changes the basic pattern of interference. This technique can be a new scheme for multi-wavelength material processing with periodic structure and will increase the variation of meta-atoms fabricated by interfering femtosecond laser processing.     

Investigating the QED vacuum with ultra-intense laser fields

In view of the increasingly stronger available laser fields it is becoming feasible to employ them to probe the nonlinear dielectric properties of the vacuum as predicted by quantum electrodynamics (QED) and to test QED in the presence of intense laser beams. First, we discuss vacuum-polarization effects that arise in the collision of a high-energy proton beam with a strong laser field. In addition, we investigate the process of light-by-light diffraction mediated by the virtual electron-positrons of the vacuum. A strong laser beam “diffracts” a probe laser field due to vacuum polarization effects, and changes its polarization. This change of the polarization is shown to be in principle measurable. Also, the possibility of generating harmonics by exploiting vacuum-polarization effects in the collision in vacuum of two ultra-strong laser beams is discussed. Moreover, when two strong parallel laser beams collide with a probe electromagnetic field, each photon of the probe may interact through the “polarized” quantum vacuum with the photons of the other two fields. Analogously to “ordinary” double-slit set-ups involving matter, the vacuum-scattered probe photons produce a diffraction pattern, which is the envisaged observable to measure the quantum interaction between the probe and strong field photons. We have shown that the diffraction pattern becomes visible in a few operating hours, if the strong fields have an intensity exceeding 10²⁴W/cm².     

Observation of radiation instabilities of a two-mode He-Ne laser with the help of interference of polarized rays

Instabilities in the operation of a two-mode He-Ne laser are observed with the help of interference of polarized beams. Two interference patterns created by two radiation modes alternatively appear. The contrast of the interference pattern increases under the action of an external constant magnetic field on the laser. If one of the interfering beams is delayed sufficiently long, the instability manifests itself in the motion of interference fringes in a direction that depends on which of the two beams is delayed. The particular features of the evolution of the interference pattern are explained based on interference equations for the two modes that take into account the orthogonality of the linear polarizations of the modes, as well as changes in their amplitudes and frequencies.     

Young’s double-slit interference pattern from a twisted beam

A wide range of diffractive elements have been used to evaluate the topological charge of Laguerre–Gaussian beams. Here, we show theoretically and experimentally that this charge can be simply and readily measured from the interference pattern in Young’s double-slit experiment. It can be evaluated from the twisting order of the interference. The results are confronted with previously published studies. The potentialities of the method are then compared with existing techniques.     

The bright and dark photon number states in Young’s interference experiment

In this paper, we derive the bright and dark photon number states for spatial interference of two or more light beams and succeed in the explanation of Young's interference experiment, and also achieve a better comprehension of the well known comment of Dirac "each photon only interferences with itself". Prom the fully quantum point of view, the origin of the interference fringes consists in the mode transformation and the detection of double-slit states.     

One-photon and two-photon double-slit interference in spontaneous and stimulated parametric down-conversions

We theoretically discuss two-photon double-slit interference for spontaneous and stimulated parametric down-conversions and compare it with one-photon case. We show that two-photon sub-wavelength interference can exist in a general interaction of spontaneous parametric down-conversion (SPDC) for both type I and type II crystals. In low gain SPDC, interference effect can be attributed to the previous study based on two-photon entangled state. But the important fact is that the sub-wavelength interference will not be washed out even if in very high gain SPDC, revealing the macroscopic nature. We propose an alternative scheme to observe sub-wavelength interference with a joint-intensity measurement, which occurs for a type I crystal in the high gain case. The theoretical analysis shows that the effect originates from classical thermal correlation. However, we also formulate the one-photon and two-photon double-slit interference in the stimulated process, and show amplified interference patterns.     

Young's double-slit experiment in photonic crystals

We present an experimental and numerical study of the transmission of a photonic crystal perforated by two subwavelength slits, separated by two wavelengths. The experimental near-field image of the double-slit design of the photonic crystal shows an interference pattern, which is analogous to Young's experiment. This interference arises as a consequence of the excitation of surface states of the photonic crystals and agrees very well with the simulations.     

Laser surface patterning using a Michelson interferometer and femtosecond laser radiation

We report on a simple method to obtain surface gratings using a Michelson interferometer and femtosecond laser radiation. In the optical setup used, two parallel laser beams are generated using a beam splitter and then focused using the same focusing lens. An interference pattern is created in the focal plane of the focusing lens, which can be used to pattern the surface of materials. The main advantage of this method is that the optical paths difference of the interfering beams is independent of the distance between the beams. As a result, the fringes period can be varied without a need for major realignment of the optical system and the time coincidence between the interfering beams can be easily monitored. The potential of the method was demonstrated by patterning surface gratings with different periods on titanium surfaces in air.     

Double-slit interference with Laguerre-Gaussian beams

The interference of Laguerre-Gaussian beams carrying orbital angular momentum was demonstrated in Young's double-slit geometry. Double-slit interference is shown to be affected by the azimuthal phase dependence of a Laguerre-Gaussian beam. This interference provides new insight into the helical phase structure of the Laguerre-Gaussian beam and has potential applications for measuring the orbital angular momentum of an arbitrary wavefront.     

部分相干电磁光束在杨氏双缝实验中的偏振特性

推导了部分相干电磁光束经过杨氏双缝干涉后偏振度的表达式,研究了干涉光场偏振度的变化情况.结果表明,干涉光场偏振度不仅取决于双缝处的偏振度、相干长度,而且还取决于杨氏双缝缝宽.当所有相干长度都相等时,干涉光场偏振度不再发生变化,其值就等于双缝处的偏振度.着重分析了系统中交叉谱密度矩阵系数Bxy=Byx≠0的情况,并将结果与Bxy=Byx=0时作了比较.     

Determination of the amplitude and the phase of the elements of electric cross-spectral density matrix by spectral measurements

The amplitudes and the phases of the elements of electric cross-spectral density matrix are determined experimentally for a pair of points in the cross-section of an expanded laser beam. A modified version of the Young’s interferometer is used as an experimental tool, which separates the beams emerging from the double-slit widely and provides ease in insertion of polarizers and half wave rotators in individual beams. To determine these complex elements of the cross-spectral density matrix, the experimentally obtained values of the spectral densities at an off-axis point are put in the mathematical expressions derived by us using the spectral interference law. The four complex generalized Stokes parameters are also determined using the linear combinations of the matrix elements. This unique but simple experimental approach for determining both the two-point parameters might provide a means to investigate the polarization and the coherence properties of the random electromagnetic beams on propagation.     

三光束激光干涉光刻的实现方法

分析了多光束空间分布产生的误差对图形的影响,通过计算优化得到三光束产生的干涉图形在整个面内有着更好的图形稳定性。利用氦镉激光光源通过特定的光学系统形成空间分布近似旋转对称的三束光, 对光致抗蚀剂进行干涉曝光,制作出了周期600 nm、高度350 nm的蜂窝状点阵,测量结果表明该系统具有很好的图形重复性和稳定性,同时降低了对于光学光路的精密性要求。     

大功率单色LED的空间相干特性

基于van Cittert-Zernike定理,从理论上计算出大功率单色发光二极管(LED)辐出光,在空间中传输后的空间相干性分布。计算结果表明,自发辐射的LED光源其辐射光在空间中传输后,由非相干光变为部分相干光,且其空间相干性与LED芯片的结构有关。实验上采用双缝干涉对LED辐射光的空间相干性进行测量,由干涉条纹的可见度与两点间的相干度之间的关系得出,非相干LED光源的辐射光在传输后为部分相干光。而采用间隔可调的双缝干涉测量两点间的相干度后发现,LED的芯片发光区域决定了其辐射光在传输中的空间相干性分布。理论计算的空间相干性分布与实验测量结果基本吻合。     

Interference from nonlocal double-slit with pseudo-thermal light

We perform an interference experiment in which a pseudo-thermal light beam illuminates two spatially separated apertures, whose superposition at the same place forms a double-slit. The experimental result exhibits a typical double-slit interference fringe in the intensity correlation measurement, in agreement with the theoretical analysis by means of the property of the second-order spatial correlation of field of the thermal light.     

非线性变周期全息光栅的制作

叙述一种用发散光束来的制作变周期光栅的方法,简单的系统保证了两束形成全息干涉的光强相等这一点对获得高反衬结构的光栅图形是重要的。在显影过程中用He-Ne激光作为衍射效率的在位监控。     

Demonstration of a recombined Fabry-Perot-Michelson interferometer with suspended mirrors

We describe preliminary experimental results concerning the operation of a 3 m arm-length Michelson interferometer with two Fabry-Perot cavities whose mirrors and beam splitter are suspended independently by wires. The reflected light beams from the two Fabry-Perot cavities are recombined to obtain interference at a photo-detector; this scheme is necessary for future power-recycled laser interferometers used to detect gravitational waves. The fundamental properties of the interferometer are presented, including the power spectral density of the displacement noise.     

Designing of interference pattern in ultra-short pulse laser processing

We have studied material processing by using an interfering ultra-short pulse laser. In this process, an interference pattern is transferred to material surface, and a periodic structure can be generated in a single shot of laser irradiation. Here, it is well known that the period of the interference pattern can be controlled by correlation angle and wavelength. In addition, a composite, doubled in density or designed interference pattern can be formed by controlling the phase shift and variation of amplitude between the interfering laser beams. In this paper, basic patterns of interference are summarized in the case of four-beam correlation.