Frequency Of Laser Beam Research Articles

Generation of a 481-W Single Frequency and Linearly Polarized Beam by Coherent Polarization Locking

We demonstrate active coherent polarization locking of two high power polarization-maintained fiber amplifiers using single frequency dithering technique. When the active phasing system is in the closed loop, a 481-W single frequency and polarization-maintained laser beam with near-diffraction-limited beam quality is generated in the circumstance of imbalanced power ratio of the two amplifiers. The beam quality ( M2 factor) of the coherently polarization locked beam is measured to be and the polarization extinction ratio of the phasing beam can be as high as 10 dB (91%).

Probing antiprotonic helium with precise lasers

Antiprotons are the antimatter counterpart of protons, which are assumed to have exactly the same mass and absolute value of charge (but opposite sign) as protons. This is a consequence of a fundamental symmetry of nature called CPT, which stands for charge conjugation, parity, and time reversal. It postulates that if all matter in the universe were replaced with antimatter, if left and right were inverted (meaning vectorial quantities such as velocity or electric field would reverse direction), and if the flow of time were reversed, this ‘anti-world’ would be indistinguishable from our normal matter world. If we could detect any deviation, however small, it would indicate that this fundamental symmetry is broken. ‘Small’ is the key word here: it is important to compare matter and antimatter with the highest possible precision. Our aim is to determine the antiproton mass in units of the electron mass, and compare it with the corresponding value for the proton to validate CPT symmetry. The proton-to-electron mass ratio is currently known to a fractional precision of 4 10 10. Particle accelerator facilities have produced antiprotons for many years, but they are notoriously difficult to handle because when antiprotons come into contact with ordinary matter, they are absorbed by the atomic nuclei and annihilate within a picosecond. However, nature provides an exception to this rule. Some of the antiprotons stopped in helium gas survive for longer due to the spontaneous formation of an exotic helium atom called antiprotonic helium (chemical symbol pHe p CHe C e , where p is an antiproton, He is a double-ionized helium atom, and e is an electron).1, 2 Within this half-matter, half-antimatter atom, an antiproton replaces one of the two electrons that normally orbit around the helium nucleus: see Figure 1. Since this antiproton orbital has a circular shape with a diameter of about 100pm that has very little overlap with the atomic nucleus, the antiproton can evade annihilation for many microseconds. The remaining electron is retained Figure 1. Schematic drawing of an antiprotonic atom (pHe) excited by two counter-propagating laser beams of optical frequencies !1 and !2. p: Antiproton. He: Double-ionized helium atom. e : Electron.

Radiation from channeling electrons, stimulated by laser beam

Fast electrons, moving in a channel formed by crystal planes, may occupy only discrete transverse energy quantum levels. Transition between levels can be accompanied with emitting high energy photons. This radiation can be additionally and resonantly stimulated by external photons having energy equal to the distance between certain channeling electron transverse energy levels in the accompanying system. Due to the Doppler effect, the optical frequency laser beam can provoke intensive γ-radiation from channeling electrons. The effect can be also used for precise resonance measuring of transverse energies of channeling electrons.

Absorption spectroscopy using interference between optical frequency comb and single-wavelength laser

Optical frequency combs have the potential to be applied not only to frequency metrology but also to various spectroscopic measurements replacing incoherent wide-frequency band light sources and single-wavelength laser sources. In this study, we propose a system of absorption spectroscopy for single electronic transitions using the frequency-comb laser source. This spectroscopic method utilizes the interference between the probing frequency comb and an additional single-wavelength laser beam and detects power spectra of beat signals in the interfered laser beam. This method enables us to measure single-transition absorption spectra neither using a large-scale spectrometer nor scanning the laser-beam frequency.

Cross focusing of two coaxial cosh-Gaussian laser beams in a parabolic medium

In this paper authors have presented the cross focusing of two coaxial cosh-Gaussian laser beams of different frequencies in a parabolic medium. Starting from the expression for field distribution of cosh-Gaussian beams, differential equations for beam-width parameters of two beams have been established through parabolic wave equation approach and analytical solution for weak beam has been obtained. The effect of decentred parameter of strong beam on the behavior of beam-width parameter with the normalized distance of propagation for weak beam has been specifically considered. The results have been presented graphically and discussed.

Parametric analysis of Nd:YAG laser marking on ceramics

Laser marking is an elegant, clean, fast and non-contact permanent marking method with high durability. The present paper deals with the analysis of laser marking process parameters like lamp current, laser scanning speed, pulse frequency, average and peak power of laser beam using Nd: YAG laser on various laser marking characteristics like the mark width, mark depth and mark contrast are studied during pulsed Nd: YAG laser marking on zirconia ceramic material. Analysis based on optical photographs has also been performed. The present study shows that high pulse frequency and lamp current with low scanning speed has more effect to achieve the minimum mark width, maximum mark depth and mark contrast. In addition to it, a multi objective optimisation has also been performed.

Experimental Study on Influence of Atmospheric Turbulence on Coherence of Dual-Frequency Laser

The influence of atmospheric turbulence on the coherence of a dual-frequency laser beam is studied experimentally. An atmospheric turbulence simulator is inserted in one arm of a Mach–Zehnder interferometer. A single frequency laser beam and a dual-frequency laser beam with a frequency difference of 100 MHz travel through the interferometer, respectively. The visibilities of the interference fringes of the single and dual-frequency laser beams under different turbulent forces are compared. When the turbulence becomes stronger, the visibilities of the interference pattern of the single frequency interferometer decrease more rapidly. This shows that the atmospheric turbulence has less influence on the coherence of the dual-frequency laser beam. The linewidths broadened by the turbulence are calculated with the Wiener–Khintchine theory.

Nonlinear diffraction and total internal reflection in optical-beam interaction in defocusing media

We elaborate the theory of reflection of an optical signal beam from an inhomogeneous channel created by a high-power laser beam of different frequency in a nonlinear defocusing medium. We study the effects of total internal reflection and nonlinear diffraction in the interaction of these beams. We derive and analyze the equation for the trajectory of the reflected signal beam and obtain the expression for the critical value of beam-intersection angle below which the total internal reflection occurs. We discuss the results of numerical modeling of nonlinear Schr¨odinger equations for envelopes of the beams in media with quadratic, photorefractive, and thermal nonlinearities. We present experimental data on the interaction of beams of argon and helium–neon lasers in a cuvette with tinted alcohol.

Laser-induced nuclear magnetic resonance splitting in hydrocarbons

Irradiation of matter with circularly polarized light (CPL) shifts all nuclear magnetic resonance (NMR) lines. The phenomenon arises from the second-order interaction of the electron cloud with the optical field, combined with the orbital hyperfine interaction. The shift occurs in opposite directions for right and left CPL, and rapid switching between them will split the resonance lines into two. We present ab initio and density functional theory predictions of laser-induced NMR splittings for hydrocarbon systems with different sizes: ethene, benzene, coronene, fullerene, and circumcoronene. Due to the computationally challenging nature of the effect, traditional basis sets could not be used for the larger systems. A novel method for generating basis sets, mathematical completeness optimization, was employed. As expected, the magnitude of the spectral splitting increases with the laser beam frequency and polarizability of the system. Massive amplification of the effect is also observed close to the optical excitation energies. A much larger laser-induced splitting is found for the largest of the present molecules than for the previously investigated noble gas atoms or small molecules. The laser intensity required for experimental detection of the effect is discussed.

Quantum tunneling and the resonant states

Using model systems we construct exact solutions of the Schr\"odinger equation for the tunneling effect in terms of the so-called resonant states. Two models of atomic ionization by an electrostatic field $E$ are studied in detail with a special emphasis on strong fields where the decay exponents become proportional to ${E}^{2∕3}$. The tunneling process, initiated by the field, is presented by an infinite sum of exponentially decaying terms without a usual slow decaying component at longer times. The sum of this series in some cases, including our models, lead to a nonexponential decay. The normalization techniques of the spatially divergent resonant wave functions via regularization of divergent integrals are considered. In particular, we apply an approximate semiclassical cutoff procedure which allows us to place the resonant states on a similar footing as the usual bound states and even use the standard normalization of the probability density. An application of such approach can illuminate and simplify calculation schemes for the study not only of ionization in electrostatic fields but also the multiphoton ionization by low frequency laser beams.

Analysis of a Tunable Asymmetrical Nonlinear Directional Coupler Using Laser Beam Interaction with Semiconductor Medium

A tunable asymmetrical nonlinear directional coupler (NLDC) having interaction of a laser beam with the semiconductor medium of the coupler has been thoroughly analyzed. The analysis is based on the coupled-mode theory for coupled lines. Laser beam is used for achieving optical control over the nonlinear directional coupler. The effects of various parameters such as plasma density, waveguide width, laser beam frequency and laser spot position on the coupling of power, on an asymmetric coupler have been investigated and presented.

Temperature Dependence of Electromagnetically Induced Transparency in a Cs Atomic Vapor Cell

The temperature dependence of electromagnetically induced transparency (EIT) in a Cs atomic vapor cell was investigated. A probe laser beam frequency was scanned around the resonance frequency of the transition line 6S1/2, F = 3 → 6P3/2, F′ = 4 while the coupling beam frequency was locked to the transition line 6S1/2, F = 4→ 6P3/2, F′ = 4. In order to analyze the temperature dependence of the EIT signal quantitatively, we calculated the dispersion slope of the EIT signal at the resonance frequency of the probe beam by taking the 2 derivative of the measured EIT signal. We found that there existed an optimum temperature at which the dispersion slope had a maximum value. This temperature dependence of the EIT signal was well explained by the calculated results considering the Doppler effect and the atomic coherence relaxation due to atomic collisions.

Role of surface plasmon in second harmonic generation from gold nanorods

The role of surface plasmon in second harmonic generation from arrays of gold nanorod particles excited by femtosecond laser pulses is investigated as a function of incident light polarization and irradiation wavelength. In addition to photoluminescence, a peak of second harmonic is observed and is found to depend on the polarization and wavelength of the fundamental frequency laser beam. In particular, the authors found similarities between extinction spectra of the nanoparticles and spectra of emmitted second harmonic. This behavior can be explained by resonant excitation of localized surface plasmon resonances.

Influence of a laser beam's frequency stability on dislocation of vortex points in an optical vortex interferometer

New applications for optical vortex interferometers (OVIs) are under investigation. The precision of the OVI depends strongly on the accuracy of positioning of the vortex points, which requires more than one interferogram (fringe pattern), so the influence of the laser beam's frequency stability is important. We present an analysis of the influence of the laser beam's frequency stabilization on the accuracy of methods locating vortex points relative to dimensions in optical arrangements of OVIs.

Effect of relativistic mutual interaction of two laser beams on the growth of laser ripple in plasma

This paper presents an effect of relativistic mutual interaction of two laser beams of different frequencies on the growth of a laser ripple in laser produced plasmas. The nonlinearity due to relativistic mass variation depends not only on the intensity of one laser but also on the second laser. Therefore, one laser beam affects the dynamics of the second beam and hence a mutual nonlinear interaction (cross-focusing) takes place. The dynamical equations governing the laser intensity of two laser beams and the perturbation present on one laser beam (ripple) have been set up and a numerical solution has been presented for typical laser plasma parameters. It is found that a change in the intensity of the second laser beam can affect the growth of the laser ripple significantly. This study is important in plasma beat wave excitation and collective laser particle accelerators.

Physical Modeling and Frequency-Response Analysis of a High-Temperature Superconducting Terahertz Photomixer

A physical modeling and a rigorous theoretical analysis consisting of the two-temperature model and the generalized transmission-line model is used to evaluate a photo-induced terahertz continuous-wave voltage from a dc current-biased high-temperature superconducting (HTS) transmission line by optical heterodyne photomixing. The electrical and optical frequency-response analyses show the amplitude of this voltage increases with increasing beat frequency and decreasing optical frequency of laser beams. Its maximum frequency is found to be limited by the gap frequency of the HTS material, which is consistent with the available experiments reported in the literature. The developed model along with our numerical simulation reveal the ways to produce a coherent traveling-wave and high-power terahertz signal with proper choice of an HTS material, bias condition, geometrical configuration, and parameters of the transmission line and characteristics of two laser beams. This HTS photomixer can play an important role in terahertz transceivers as broadly tunable local oscillators with low-noise/low-power consumption characteristics.

Theoretical and experimental study of Bragg modulational instability in a dynamic fiber grating

We study theoretically and experimentally nonlinear wave propagation in dynamic optical Bragg gratings. Such gratings are obtained through cross-phase modulation with the beating wave that results from two intense laser beams of different frequencies propagating in a highly birefringent fiber. We show that wave propagation in these gratings obeys the standard coupled-mode equations of static nonlinear Bragg gratings, which makes our study relevant to a wide class of problems related to nonlinear wave propagation in periodic media. The main advantage of the dynamic Bragg gratings is that they make it possible to study experimentally nonlinear wave dynamics close to the bandgap where static gratings cannot be investigated because of their high reflectivity. We illustrate this advantage through the study of Bragg modulational instability.

Electromagnetically induced transparency and absorption in a standing wave

A thermal vapor of three-level atoms irradiated by two copropagating laser beams of suitable frequencies exhibits the phenomenon of coherent population trapping, leading to an electromagnetically induced transparency (EIT). When a mirror reflects the beams back onto themselves one finds that depending on the position along the resulting standing wave the fluorescence intensity from the sample (cesium in our case) decreases (EIT) or even increases [electromagnetically induced absorption (EIA)] with a period on the centimeter scale. An intuitive picture is based on the interference of coherent dark states but the explanation of the EIA effect requires consideration of Doppler effects in the thermal vapor. This allows for a quantitative comparison between experimental and calculated results.

Analysis of electron acceleration in a vacuumbeat wave

We present an exact analytic investigation of the electrondynamics in the field of two linearly polarized interferingcopropagating laser beams of different frequencies, arbitraryintensities, and arbitrary relative polarizations. In one part ofthe paper, the laser fields are modelled byplane waves and in another part the fields are allowed to haveone-dimensional sin2 pulse shapes which model focusing in thepropagation direction. The general situation in which the electron isinjected at an angle with the common direction of wave propagation isconsidered throughout. A cycle-by-cycle analysis of the electronmotion, and its momentum and energy exchange with the laser fields isconducted. It is found that an electron may be accelerated, evenfrom rest, to GeV energies over short distances using present-daylaser field intensities. This leads, in principle, to energygradients in the TeV m-1 range. The trajectory calculations alsoshow clearly that the electron gets scattered away from itsinitial direction of motion during interaction with the laser fields. Thetransverse as well as longitudinal motions may be followedexactly using our equations, and predictions could thus be madeconcerning where the electron should, in principle, be ejected inorder for it to emerge with a particular energy gain.

Study on the relationship between laser processing sound and material removal characteristics

Laser processing is an important manufacturing technology in machining difficult-to-cut materials. It is known that a sound is generated when laser processing is carried out, the intensity of the sound changing according to the processing conditions. The purpose of this research is to clarify experimentally the relationship between the material removal characteristics and the pressure level of the processing sound when a low and a high frequency laser beam are applied to the processing of ceramic materials.