Waist Position Research Articles

Investigation of the Impact of the Pumping Beam Waist Size and Position on the Efficiency of YVO4/Nd : YVO4/YVO4 Laser Generation

This article presents the results of the investigation of the generation efficiency for different sizes and positions of the pumping beam waist inside the active medium of the YVO4/Nd : YVO4/YVO4 lasers. The measurements were carried out for a fixed resonator length of 36.1 mm, a constant pumping power of 1.16 W, and four output couplers with different radii of curvature. According to the knowledge of the authors, such an extended experimental approach is presented for the first time.

Stability analysis of U-shaped horizontal salt cavern for underground natural gas storage

More and more attentions are being paid to horizontal salt caverns for natural gas storage because of their large working gas capacity and favorable stability. To accelerate the construction of gas storage underground salt caverns, stability analysis of this type of cavern is necessary to assure the safety of such caverns. In this paper, the stability is investigated of a U-shaped horizontal salt cavern under different constant and cyclic internal gas pressures. A 3D geomechanical model is established based on sonar scanning in the field and predicted cavern shape. The stability is analyzed of the rock masses around the cavern under different internal gas pressures and cycle frequencies. Five evaluation criteria are proposed to predict the feasibility and stability of such caverns, including deformation, dilatancy safety factor, volume shrinkage, plastic zone, and equivalent strain. The stability of the rock mass around the cavern under different internal gas pressures is compared to that under different cycle frequencies. The results show that the cavern has a good stability under the constant internal gas pressure of 8 MPa and cyclic internal gas pressures ranging from 8 ~ 18 MPa. The five evaluation indexes of the rock masses around the cavern improve with increasing internal gas pressure. It is proposed that the corner, horizontal-roof center, and external waist positions of the cavern are to be highlighted in the design and construction phases. The cycle frequency has appreciable impact on the stability of the rock mass around the cavern. The difference between the volume shrinkage under cycling compared to constant internal gas pressure is that the cycling simulated results show a rising wave-like curve of creep time. The plastic zone ratio increases with creep time and has a flat peak and a sharp bottom with oscillations. This study provides the design parameters for U-shaped salt cavern in the Huaian salt district and can also be a reference for horizontal salt caverns.

Fractional Angular Momenta, Gouy and Berry Phases in Relativistic Bateman-Hillion-Gaussian Beams of Electrons.

A new Bateman-Hillion solution to the Dirac equation for a relativistic Gaussian electron beam taking explicit account of the four-position of the beam waist is presented. This solution has a pure Gaussian form in the paraxial limit but beyond it contains higher order Laguerre-Gaussian components attributable to the tighter focusing. One implication of the mixed mode nature of strongly diffracting beams is that the expectation values for spin and orbital angular momenta are fractional and are interrelated to each other by intrinsic spin-orbit coupling. Our results for these properties align with earlier work on Bessel beams [Bliokh etal., Phys. Rev. Lett. 107, 174802 (2011)PRLTAO0031-900710.1103/PhysRevLett.107.174802] and show that fractional angular momenta can be expressed by means of a Berry phase. The most significant difference arises, though, due to the fact that Laguerre-Gaussian beams naturally contain Gouy phase, while Bessel beams do not. We show that Gouy phase is also related to Berry phase and that Gouy phase fronts that are flat in the paraxial limit become curved beyond it.

Photothermal lens spectrometry: Experimental optimization and direct quantification of permanganate in water

• An optimization of Thermal Lens Spectrometry (TLS) experiment was made. • The TLS method is appropriate for permanganate quantification in water treatment application at neutral pH. • The Limits of Detection are 0.22 μM and 0.08 μM for distilled and tap water, respectively. Although permanganate is a widely used oxidant in drinking water and wastewater treatment, only few spectrometric methods were proposed for measuring its concentration in water. The thermal lensing spectrometry (TLS) experiment was optimized and applied for the quantification of trace permanganate in water at neutral pH. Several parameters (probe beam waist position, confocal parameters and detector position) influencing the thermal lens (TL) signal were explored in order to optimize the geometry of mode-mismatched dual-beam experiment. Based on the obtained experimental and theoretical results, the TL signal reaches an amplitude that is two times larger than that obtained with the collimated method. As application of this experiment, I have measured the limit of detection (LOD) and quantification (LOQ) of permanganate in distilled and tap water without the need of reagents. The obtained results of LOD are 0.22 μM and 0.08 μM for distilled and tap water, respectively. These values are better than those obtained by the conventional absorption spectrometry method which is suitable for samples containing more than around 5.5 μM, and close to the LOD achieved by indirect spectrometric methods.

Frequency doubling of acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded Raman laser for narrow pulse-width 657 nm laser

Frequency doubling of second-Stokes in an acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Raman cavity is demonstrated to achieve a narrow pulse-width red laser. A three-stage bonded YVO<sub>4</sub>/Nd:YVO<sub>4</sub>/YVO<sub>4</sub> crystal is designed by comprehensively considering the improvement of thermal effect, the performance of fundamental frequency laser and Raman conversion, to improve the Raman efficiency and output power. An LBO crystal cut for critical phase matching at room temperature is selected and used as a nonlinear optical crystal for realizing the frequency doubling of second- Stokes wave. Its phase matching angle (<i>θ</i> = 86.0°, <i>φ</i> = 0°) is very close to the non-critical phase matching angle and has a small walk-off angle, which is beneficial to the realizing of the high conversion efficiency of frequency doubling. In the experiment, the beam waist position of the pump light and the repetition frequency of the acousto-optic Q-switcher are optimized. Under an incident pump power of 14.2 W and a repetition frequency of 60 kHz, the highest average output power of 1.63 W and conversion efficiency of 11.5% are obtained for the 657 nm red laser emission. The pulse width of 657 nm red light is 11.5 ns at the maximum output power, which is much narrower than that generated by frequency doubling of ordinary neodymium-doped laser at a waveband of 1.3 μm. The result shows that the frequency doubling of the acousto-optic Q-switched Nd:YVO<sub>4</sub> cascaded self-Ramanlaser can take advantage of the pulse-width compression characteristics of Raman process to achieve a narrower pulse-width red light laser output.

Electron-Optic System With a Converged Sheet Electron Beam for a 0.2-THz Traveling-Wave Tube

This article presents the results of a design study of an electron-optic system (EOS) for a sheet-beam ${G}$ -band traveling-wave tube. An electron gun providing a 0.1-A, 20-kV sheet beam emitted by a 0.8 mm $\times0.8$ mm curved cylindrical cathode is designed. The beam dimensions at waist position are 0.05 mm $\times0.8$ mm with a compression ratio of 16 in the vertical direction. A magnetic system providing 1.1 T magnetic field, which is nearly seven times higher than the Brillouin field, is designed, and beam transmission in the 0.1 mm $\times0.85$ mm beam tunnel is studied by 3-D particle-in-cell (PIC) simulation. It is demonstrated that the beam has a complex structure of particle distribution, i.e., a high-density central part (core) and a peripheral low-density part (halo). The effect of assembly tolerance on beam transmission is studied. The prototype gun is fabricated, which compresses the beam to 0.1 mm by electrostatic field only. The 135-mA current with 95% transmission through the 0.2-mm anode aperture is measured.

Propagation characteristics of focused astigmatic Gaussian beams in Kerr nonlinear media

When a powerful laser beam propagates in a Kerr nonlinear medium, the Kerr effect on the beam propagation characteristics is very significant. The astigmatic laser beams are often encountered in practice. Until now, much work has been carried out on the propagation characteristics of astigmatic laser beams in linear media, but a few researches have been reported about the propagation of astigmatic laser beams through nonlinear media. To the best of our knowledge, the propagation or the transformation of astigmatic laser beams through an optical system in a Kerr nonlinear medium has not been investigated. In this paper, the propagation characteristics of focused astigmatic Gaussian beams in a nonlinear Kerr medium are studied. The Kerr effect on the beam astigmatism and the focal shift of focused astigmatic Gaussian beams are investigated in detail, and the self-focusing focal length and focus control of focused astigmatic Gaussian beams in the Kerr nonlinear medium are also studied. For the beam spreading case, the analytical formula for each of the beam width, the beam waist position, and the focal shift of focused astigmatic Gaussian beams in the Kerr nonlinear medium is derived. It is shown that in the self-focusing medium, as the beam power increases (i.e. the self-focusing effect becomes stronger), the beam astigmatism becomes stronger, but the focal shift decreases. However, in a self-defocusing medium, as the beam power increases (i.e. the self-defocusing effect becomes stronger), the beam astigmatism becomes weaker, but the focal shift increases. On the other hand, for the beam self-focusing case, the analytical formula of the self-focusing focal length of focused astigmatic Gaussian beams in the Kerr nonlinear medium is derived. It is found that the number of foci can be controlled by applying beam astigmatism. The results obtained in this paper are of theoretical and practical significance.

Comparison between dry needling plus manual therapy with manual therapy alone on pain and function in overhead athletes with scapular dyskinesia: A randomized clinical trial

Muscles’ trigger points can induce scapular dyskinesia (SD) which interferes with overhead athletes' professional training. We aimed to evaluate effects of dry needling (DN) alone and plus manual therapy (MT) on pain and function of overhead athletes with SD. 40 overhead athletes (15 male, 25 female) aged 18–45 with at least 3 points Numeric Rating Scale (NRS) pain intensity during training were recruited and randomly allocated to the treatment group: MT followed by DN on trigger points of Subscapularis, Pectoralis minor, Serratus anterior, upper and lower Trapezius muscles; or the control group: MT alone. The effect of shoulder trigger points DN plus MT with MT alone on pain, function, Pain Pressure Threshold (PPT) and SD in athletes with SD were compared. Both the examiner and the therapist were blinded to group assignment. Both groups were analyzed. Pain, disability and SD were improved in treatment group (P < .05). On the other hand, when only MT was applied, despite reduction in pain and disability (P < .001), scapular slide only improved in hands on waist position. Comparing the differences between groups showed a substantial reduction in pain (P < .001) and disability (P = .02) with significant improvement in scapular dyskinesia in treatment group (P = .02). Moreover, PPT significantly increased in the control group (P = .004). No adverse effects reported by the participants during this study. DN is an easy and applicable method that can synergistically reduce pain, disability and dyskinesia when it is combined with manual techniques to treat shoulder dysfunctions.

Afocal combinations and focus control for laser launch telescopes

In the field of ground-based telescopes, laser guide stars (LGS) are artificial stars formed in the sky to serve as a reference for the adaptive optics. The artificial star should have a small lateral extent as this is an important factor for how well the adaptive optics can compensate for atmospheric turbulence. The laser launch telescope (LLT) is a key component of the LGS facility. It uses an afocal system to increase the waist of the laser, therefore reducing the beam divergence and limiting the size of the star. We describe the design process of LLTs and show how a combination of two afocals with controlled defocus can be used to optimize the LGS. First, the impact of defocusing a single afocal and tuning the position of the input beam waist is presented. We then demonstrate how an intermediary afocal system can be used to vary the properties of the beam at the input of the second afocal. With such a configuration, a controlled defocus of both afocals can be performed to tune the artificial star size. Moreover, the two afocals configuration can be used to adapt the system to the amount of atmospheric perturbations affecting the beam during the upward propagation.

Propagation characteristics of Gaussian-Schell model beams through optical systems in Kerr media.

For the beam spreading case, the propagation formulae of Gaussian-Schell model (GSM) beams through general optical systems in Kerr media are derived, and the propagation characteristics of GSM beams through an ideal thin lens in Kerr media are studied in detail. It is shown that the size and position of the beam waist can be controlled by the Kerr effect. Furthermore, the formula of the focal shift of the GSM beams focused by an ideal thin lens in Kerr media is also derived. It is found that in self-focusing media the focal shift decreases as the beam power or the beam coherence degree increases. In addition, there exists a maximum of the focal shift, and the formula of the focal shift maximum is derived. On the other hand, for the beam self-focusing case, the focusing characteristics of GSM beams focused by an ideal thin lens in Kerr media are also investigated.

Refractive index and temperature sensor based on cleaved taper and spherical structure

An in-line Mach-Zehnder interferometer (MZI) for simultaneous measurement of temperature and refractive index (RI) is proposed and demonstrated. The sensor is composed of cleaved taper, single-mode fiber (SMF) and spherical structure. Using precision device to measure the position of waist, the cleaved taper structure is obtained by cutting the taper structure. The sensitivities of the temperature are 0.052 nm/ °C and 0.037 nm/ °C in the temperature range of 25–70 °C, respectively. The RI sensitivities are −56.59 nm/RIU and −43.53 nm/RIU in the RI range of 1.335–1.38, respectively. This sensor has many advantages such as compact structure and good stability.

A Method for Coupling Monte Carlo Simulations of Photon Transport to Focused Gaussian Beam Propagation

We present a method for modeling focused Gaussian beams in turbid media. Compared to previous methods based on ray tracing, our method is simple and fast. Rather than sampling photon launch positions from the surface of the media, we directly sample launch positions from inside the sample volume using the probability distribution for the position that a ballistic photon will first interact with the tissue. The examples presented illustrate the importance of accounting for Gaussian beam optics when simulating a focused beam. Not doing so will give an artificially large irradiance at the beam waist position. Thermal models used to predict laser damage to tissue will predict temperature rises that are too large for samples containing the beam focus.

Thermal elastohydrodynamic lubrication characteristics of double involute gears at the graded position of tooth waist

Abstract According to the meshing characteristics of double involute gears, a method for calculating its contact line length and equivalent curvature radius is proposed. Based on the EHL theory, established a thermal EHL calculation model for double involute gears at the graded position of tooth waist considering the characteristics of non-Newtonian fluid. The thermal EHL characteristics between the graded position of the tooth root and top are different. The variation of the tooth waist order parameters can influence the lubrication performance at the graded position of the tooth waist, and compared with the isothermal solutions, the influence of thermal effect on the EHL characteristics is unremarkable at this location.

Realization of a high power optical trapping setup free from thermal lensing effects.

Transmission of high power laser beams through partially absorbing materials modifies the light propagation via a thermally-induced effect known as thermal lensing. This may cause changes in the beam waist position and degrade the beam quality. Here we characterize the effect of thermal lensing associated with the different elements typically employed in an optical trapping setup for cold atoms experiments. We find that the only relevant thermal lens is represented by the TeO2 crystal of the acousto-optic modulator exploited to adjust the laser power on the atomic sample. We then devise a simple and totally passive scheme that enables to realize an inexpensive optical trapping apparatus essentially free from thermal lensing effects.

Daily Motion Recognition System by a Triaxial Accelerometer Usable in Different Positions

Human–computer interaction has been a more popular research field in recent years with the escalating interest in wearable systems. In this context, evaluating the details of the physical movement of the human body has become a prominent subject for researchers. The systems, which are yielded from this subject, are utilized in such areas as health, public safety, access control, and smart home systems. This kind of system is expected to give fast and reliable results and can be used comfortably for the user. In this paper, a fast and accurate system design about recognition of daily human activities, including falls in the elderly, is proposed. In addition, another main objective of the study is to examine whether an accelerometer can be set in different positions during person’s daily activities. Motion data have been acquired from the waist, wrist, and knee positions of 5 female and 15 male volunteers using a three-axis accelerometer. In this way, walking, sitting, standing up, jumping, and falling motions were collected from volunteers. The principal component analysis method was used as a feature reduction method to reduce the process time and get quick results. Furthermore, any feature extraction method was not used. The support vector machine, multi-layer perceptron, radial basis function, and Naive Bayes classifiers were employed to perform classification success. The proposed technique achieved a maximum of 100%, an average of 96.54% accuracy on the three defined positions. As a result, it has been determined that a single accelerometer can be set in different positions. The findings also suggest that this method can be used in home care and follow-up procedures and fall detection for elderly people.

Diffraction of a Gaussian beam near the beam waist

The behavior of the light field near the beam waist has attracted considerable attention due to the studies of the light spin-orbit interaction: it’s manifestation as well as potential applications. Similarly, the light beam diffraction can reveal new light particularities. We have studied the far-field diffraction of a Gaussian beam by a half-plane edge placed near the beam waist. We have solved numerically the Helmholtz equation using the spectral method. We have found symmetric penetration of the light energy into the shadow region if we placed the half-plane edge exactly in the beam waist region. The symmetry gets broken down as the edge moves along the optical axis toward or away from the lens at a distance more than 0.01% of the focal length. Experimental verification has been obtained using a Gaussian beam focused by a lens of 4 cm focal length.The results can be used for precise determination of the beam waist position while investigating the effects of the light spin-orbit interaction in focused Gaussian beams.

Occupational and Patient Doses in Interventional Cardiology in Indonesia: A Preliminary Result

Interventional cardiology is a branch of cardiology that manages the catheter based treatment of structural heart illnesses. These minimally invasive procedures involve inserting catheters and other devices through superficial arterial and venous access sites. Due to increased reliability and advancing technology, the number and complexity of interventional cardiology procedures haves increased in recent years. The increasing complexity of the procedures, however, require longer fluoroscopic duration, leading to increased exposure time to ionizing radiation for the patient and also for the medical staff since they need to remain close to the patient throughout the procedure. This study attempts to investigate the occupational and patient doses during the course of several interventional cardiology procedures in Indonesia, i.e. CA, PCI, cathscan, PA, PTCA, TACE, PAC and peripheral vascular. Occupational doses were measured by using individually packed three chips of TLD-100 placed in over- and under-thyroid shield used by medical staff, over- and under-apron in waist position, inside a special ‘eye-D’ holder, and inside a ring holder, while patient doses were estimated by using individually packed three TLD-100 chips attached in the x-ray tube. All TLDs were calibrated in the Secondary Standard Dosimetry Laboratory (SSDL) Jakarta. The study was performed in three big hospitals in the cities of Jakarta, Yogyakarta and Semarang. The results show that PCI procedure was the most performed one during the course of this study and gave the highest radiation doses to the staff for all type of doses calculated and measured. The maximum effective doses, eye lens doses, extremity doses, thyroid doses and gonad/ovary doses were 0.098 mSv, 0.1967 mSv, 0.7604 mSv, 0.1760 mSv and 0.0990 mSv, respectively. In the case of patient doses, the mean value of DAP for PTCA procedure of 776.76 Gy cm 2 was the highest compared with those for other procedures. The results of measurement for occupational doses were in general similar to those reported by other authors, but not for patient doses that was found to be 4-5 times higher. Due to the involving of various parameters during the course of interventional cardiology procedures, it was difficult to establish a correlation between the doses received by medical staff and by the patients. 800x600 Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:Table Normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif;}

A Multiobjective Optimization Design Tool for Traveling-Wave Tubes’ Electron Optics System

The nondominated sorting genetic algorithm II and the electron optics simulator were combined to form a multiobjective optimization design tool for electron optics systems of traveling-wave tubes. After determining the objective functions that vary with the macroscopic electrical parameters that need to optimize the electron optics system, the optimization tool is capable of obtaining the optimal solution set automatically. Then, the microscopic electron trajectories of the individuals in the optimal solution set are analyzed to get the final scheme. In the collector optimization, the maximum collector efficiency and the minimum back-streaming current are used as optimization goals. While for the demonstrated electron gun, the maximum waist position is set to be the optimization goal, together with constraints of emitting current and beam waist radius. After analyzing the energy density distribution on the collector inner surface or the laminar flow of the electron gun, the final scheme is determined from the optimal solution set.

Dual-wavelength end-pumped Rb-Cs vapor lasers.

Diode-pumped alkali vapor lasers (DPALs) have been rapidly developed because of their excellent performances. However, there have been few reports about DPALs with multiple wavelengths until now. The effects of the output features on the waist size and position of both Rb and Cs pump beams were first theoretically investigated using a kinetic model for an end-pumped dual-wavelength Rb-Cs laser. Then, a continuous-wave (CW) laser was experimentally constructed. Finally, the hybrid CW-modulated output with two wavelengths was also successfully obtained for the first time in development of alkali lasers. The results might be helpful in applications for laser communication and ranging/radar in the future.

In situ real-time beam monitoring with dielectric meta-holograms.

A novel approach for performing in situ and real-time beam monitoring, based on dielectric meta-hologram, is proposed and demonstrated. The ultrathin dielectric meta-hologram projects a portion of the beam power onto a screen to provide a visual indicator of the spatial intensity distribution of a Gaussian laser beam, as well as its waist position along the optical axis. Specifically, we demonstrate simple monitoring of the spot size, astigmatism, lateral position, and position along the optical axis of the beam. Good agreement is found with both theory and conventional knife-edge beam profiler measurements. This in situ beam monitoring approach could provide a highly useful tool for numerous optical applications.