Photonic jet μ-etching: from static to dynamic process

The study of accelerating Airy-family beams has made significant progress, not only in terms of numerical and experimental investigations, but also in conjunction with many potential applications. However, the curvature of such beams (and hence their acceleration) is usually greater than the wavelength. Relatively recently, a new type of localized wave beams with subwavelength curvature, called photonic hooks, was discovered. This paper briefly reviews the substantial literature concerning photonic jet and photonic hook phenomena, based on the photonic jet principle. Meanwhile, the photonic jet ensemble can be produced by optical wave diffraction at 2D phase diffraction gratings. The guidelines of jets’ efficient manipulation, through the variation of both the shape and spatial period of diffraction grating rulings, are considered. Amazingly, the mesoscale dielectric Janus particle, with broken shape or refractive index symmetry, is used to generate the curved photonic jet—a photonic hook—emerging from its shadow-side surface. Using the photonic hook, the resolution of optical scanning systems can be improved to develop optomechanical tweezers for moving nanoparticles, cells, bacteria and viruses along curved paths and around transparent obstacles. These unique properties of photonic jets and hooks combine to afford important applications for low-loss waveguiding, subdiffraction-resolution nanopatterning and nanolithography.

Photonic jet microscopy is a technical field of microscopy applying photonic jet phenomenon to increase the resolution of objects or area of objects being observed. Mostly it is used in optical microscopy as the demand of visual observations are increased, especially for the micro-metric biological objects. In addition to our previous works inoptical assessment of observing a micrometric object under a microsphere using an optical microscope, now we made the electromagnetic assessment. It concludes if smaller microsphere magnifies greater than bigger microsphere. Therefore, applying photonic jet microscopy for visual observation is getting closer.

This paper presents a study focusing on a fabrication process to shape an optical fibre tip capable of producing a photonic nanojet. Photonic nanojet generated in the near field of a dielectric bead have been comprehensively studied. Contradicting the usual laws of optical geometry, this propagative, slightly diverging, light beam can have a Full Width at Half Maximum smaller than a half-wavelength, subsequently going beyond the diffraction limit. Thanks to these useful properties, the photonic nanojet is an ideal tool for near-field optical microscopy and subwavelength micromachining. Nevertheless, for a repeatable and industrial processes, one need to bypass the use of dielectric beads that are tedious to manipulate. A photonic jet can also be generated at the end of a shaped optical fiber tip. Optical fibres are commonly shaped by various methods revolving around thermoforming. Unfortunately, the thermoforming process has some limitations: controlling the curvature of the tip is hazardous and the effect on the diffusion of the dopant in the core and cladding is unknown. Nonetheless, other approaches to optical fibre shaping have been investigated by the scientific community. A promising method, further investigated in this work, is chemical etching with hydrofluoric acid. The process, often labelled as highly hazardous due to the nature of the chemical involved, offers a great way to carefully shape the tip of silica based-fibre. The optimisation of the fibre tip shape, in order to get the desired photonic jet, was made by 2D modelisation, by finite elements method. The wanted tip shape is then obtained by thermoforming, chemical etching and the combination of two methods. The thermoforming was done by electric arc. The isotropical etching was performed in a solution of 24 % HF. The characterisation of the fibre tips was carried out by the direct ablation of silica and photosensitive resin insulation using respectively 1064 nm and 514 nm lasers. The results were studied by optical microscopy and white light scanning interferometry. Insulated spots of 3.5 µm were measured on SU8. Ablated spots of 685 nm were observed on silica. These encouraging results prove that the combination of thermoforming and chemical etching can lead to highly accurate fibre tip shaping for Photonic NanoJet generation and thus open the way to enhanced sub-wavelength Material Laser Processing.

Photonic jet in terahertz (THz) frequency range (terajet) plays an important role in modern THz scanning systems to achieve a superresolution beyond the diffraction limit. Based on analytical simulations, we introduce a synergetic effect of a mesoscale dielectric sphere and graphene to improve the focusing properties of a particle. We show that a graphene-covered dielectric sphere is able to enhance the field behind it if the refractive index is high. This conflicts with a generally accepted statement that a jet is generated only for low-index dielectrics with n < 2. We demonstrate the tunability of the terajet characteristics with respect to the graphene Fermi energy and discover a Fano resonance causing the field increase. This design leverages the tuning properties of the graphene allowing dynamic control over the power and size of the generated terajet in real time. With high-index materials, we get the opportunity for integration of terajet-assisted imaging with semiconductor technology.

Chirp backscattering by pec sphere eccentrically placed in a dielectric sphere

For the purpose of utilizing changes in speckle patterns to be observed in an output light spot from an optical fiber for sensing applications, certain load was applied onto an optical fiber in which laser beams from a laser diode were propagating, and resultant changes in the output light intensity were measured. In order to realize effective load application onto the optical fiber, load application mechanism was employed in which several ridges were intentionally provided onto opposite flat plates. A jacket-covered communication-grade multi-mode glass optical fiber was placed in the load application mechanism so that corrugated bending of the fiber was intentionally induced via load application due to the ridges. Laser beams propagated through the optical fiber was allowed to be output and projected onto a PV cell panel disposed at about 10 cm from the fiber end. The output voltage from the PV cell panel was measured as the output light intensity from the optical fiber. For the load application up to 40 kg, certain changes (reductions and increases) in the output light intensity were measured with increasing or decreasing level of load application with sufficient reproducibility. Even with load application of smaller load level, similar changes were observed. Such changes (reductions and increases) in the output light level with increasing and decreasing load application levels were caused by changes in speckle patterns contained in an output light spot from the optical fiber.

High power Nd:YAG laser beam with wavelength 1.064micrometers , pulse-width 20 and 100 pico-second was focused onto Zn coated target; and separated by beam splitter and delivered via optical fibers. Some key problems of ultra short pulsed high power laser beam transporting in optical fiber were involved and solved; laser ablation effect by laser irradiation and after optical fiber transportation were comparatively studied. Ablation rate was defined as ablated volume to laser fluence and used as a description of ablation ability. The relationship of ablation rate with laser fluence was plotted and optimum condition was found. Corresponding to the optimal condition, ablation effect in cases of 20 and 100 pico- second pulse-width, 90 degree(s) and 20 degree(s) laser incident angles, using spherical lens and cylindrical lens for laser beam focusing was compared respectively. It was shown that if other conditions unchanged, used spherical lens and cylindrical lens, ablation rate was almost same, but it was high as pulse-width equal to 100ps or laser incident angle equal to 90 degree(s) than as 20ps or 20 degree(s) respectively. In addition, laser beam over 5.6 watt, transporting rate near 90 per was output at the end of the optical fiber. Using the laser was this output power, the same thickness Zn coating was completely removed. Basing on this experiment, the possibility of laser surface ablation cleaning under complicated circumstance was confirmed.

This paper reports the fabrication of various micro-lensed single-mode optical fibers through the use of an enhanced peak power $CO_2$ laser beam. The end faces of the optical fibers are exposed to the $CO_2$ laser beam to form convex, concave, and conical shape optical fiber tips. Peak power of the $CO_2$ laser beam was varied from 0.8 W to 1.5 W depending on the shape of the optical fiber tip. We also discover the dependence of the angle of the optical fiber tip on the rotation angle and the number of $CO_2$ laser irradiations. The angle shows an increasing trend with both these parameters. We achieve a wide range of lenticular fibers with end face angle varying from $4.47^{\circ}$ to $8.13^{\circ}$ . Furthermore, we investigate the emission pattern of light from the developed micro-lensed fibers. The proposed $CO_2$ laser based optical fiber reshaping technique shows great consistency, and thus is suitable for commercial applications.

Single frequency fiber laser is the most promising optical source in fibre optic communication, which plays an important role in fibre optic sensor, laser radar and laser range finde. Generally, the performance of the single frequency fiber laser was evaluated by the phase noise. The oscilloscope and dynamic signal analyzer method were adopted to design phase noise of single frequency fiber laser. Using power spectrum and the integral sources of different pump power, seed source power and wavelength of the fiber laser phase noise were analyzed qualitatively, the results show that, the greater pump power can get the low frequency phase noise. For the different seed source powers, phase noise is in the proportion of basic test frequency at the same level. For testing seeds of different wavelengths which is different proportions of high frequency phase noise, the biggest percentage of seed wavelength is 1 560.48 nm.

We demonstrate bright pictures in the pixel format of HDTV and XGA with a current power consumption lower than 2.5 kW and a RGB laser output power of 15 W with the wavelengths 446 nm, 532 nm and 629 nm. The laser projection system consists of a scanning unit with a rotating polygon scanner (rotational frequency up to 2 kHz) to write the lines and a galvanometer scanner for the vertical deflection of the lines. The system allows the separation of the RGB-laser with the video modulation part from the free moving scanning unit with an optical fiber. The optical fiber provides the video modulated RGB-laser power in a collinear beam to the scanner. We explain detailed the requirements for RGB--laser beams. The main demands for high resolution and sharp scanned pictures are near diffraction limited laser beams, but at least with an optical beam product of < 0.75 mm mrad. Furthermore we give an outlook for an increase of pixel resolution.

Laser cladding, which is one of laser metal deposition (LMD) technologies, is an effective metal surface coating technique capable of increasing component lifetimes, in which an additive material such as a powder or a wire is melted by a laser beam and deposited on the substrate surface. We developed a multi-beam processing head with six high intensity infrared (IR) diode lasers, which was based on multi laser combining method, in order to realize a high quality cladding layer having a dense, fine and purity. An IR diode laser light with the power of 50 W was output from an optical fiber. Total laser power on the base plate was 300 W since six laser beams were overlapped. A nozzle to supply the powder was in the center of the processing head. The processing head was installed in a machine tool (simultaneous 5-axis machining). Hardness and abrasion resistances of blade edge and shaft made from stainless steel were improved by cladding of cobalt-base alloy powder, which was one of the applications with the machine. We also designed a multi-beam processing head with high intensity blue diode lasers for cladding of copper powder. We have developed a high intensity blue diode laser with the power of 100 W. The blue laser light was output from an optical fiber whose core diameter and NA were 100 m and 0.22, respectively. The three blue diode lasers would be installed to the processing head to obtain the power of 300 W on the base plate

The objective of this work is to study the performance of the Nd:YAG laser to cut thick free standing CVD diamond films. The high flexibility of this type of laser, given by the possibility to guide the laser beam by means of an optical fibre represents a great advantage in order to automate the cutting process in the production lines. Laser cutting technology is imperative to shape non-conductive CVD diamond parts for electronic, optical and mechanical applications, namely heat sinks, infrared transparent windows and small tips to braze onto machining tool holders. Concerning diamond tool production, the rapid cutting method by laser here proposed provides an advantage to CVD diamond when compared to conventional polycrystalline diamond (PCD) blanks that are cut by the Electro-Discharge Machining (EDM), a time-consuming and very expensive technique due to the electrodes cost.Free-standing diamond films were grown on silicon wafers by microwave plasma chemical vapour deposition (MPCVD) method in a ASTeX PDS 18 unit. The diamond growth parameters were: microwave power 4.35kW; total pressure 110Torr; H2 flow 400s.c.c.m.; CH4 flow 30s.c.c.m; deposition time 70h. The final film thickness was approximately 500μm. The diamond plates were then released by chemical dissolution of the Si substrate in a nitric/hydrofluoric acids mixture. The equipment employed to perform the cutting experiments consisted of a pulsed Nd:YAG laser delivering a maximum average power of 500W at a wavelength of 1064 nm. The laser beam was coupled to an optical fibre of 400μm diameter and 10 m long. The pulsed beam coming out of the fibre was focused onto the surface of the free standing diamond coating by means of a commercial cutting head, having a lens of 80 mm focal length, in which the laser beam was coaxial to the Ar gas jet used as assist gas.In this paper we discuss the results of the work carried out to analyse the influence on cuts quality of laser processing parameters such as: cutting speed 5-20mm/s; pulse width 0.3-1ms; pulse energy 0.8-4.6J; power 80-470W. Scanning electron microscopy was used to look into film cracking events and to appraise the cut width and linearity. Micro-Raman spectroscopy allowed the evaluation of the graphitisation level on the cut surface.The objective of this work is to study the performance of the Nd:YAG laser to cut thick free standing CVD diamond films. The high flexibility of this type of laser, given by the possibility to guide the laser beam by means of an optical fibre represents a great advantage in order to automate the cutting process in the production lines. Laser cutting technology is imperative to shape non-conductive CVD diamond parts for electronic, optical and mechanical applications, namely heat sinks, infrared transparent windows and small tips to braze onto machining tool holders. Concerning diamond tool production, the rapid cutting method by laser here proposed provides an advantage to CVD diamond when compared to conventional polycrystalline diamond (PCD) blanks that are cut by the Electro-Discharge Machining (EDM), a time-consuming and very expensive technique due to the electrodes cost.Free-standing diamond films were grown on silicon wafers by microwave plasma chemical vapour deposition (MPCVD) method in a ASTeX P...

A method for injecting a high peak power multimode laser beam into an optical fiber has been developed. The design minimizes the peak irradiance on the fiber's entrance face and reduces its dependence on the laser's mode structure and the system alignment. A simple lens and a specially designed kinoform (or binary optics element) operate together to transform a 5 mm diameter laser beam into two concentric ring foci that fit on the 400 micrometers diameter fiber face.

Optical Seismology![Figure][1] A subsea cable coiled on board a ship, ready for deployment CREDIT: RUN STUDIOS Seismic networks detect earthquakes and are common on continents, where they are easy to install. However, most of Earth's surface is under the oceans, where placing seismometers is difficult. Marra et al. now find that ordinary submarine telecommunication cables can be used to detect earthquakes. Small strain changes associated with the passage of seismic waves were detected with laser light sent through in-use fiber optic cables by ultrastable lasers. This strategy could turn intercontinental fiber optic cables into ocean-bottom strain sensors, dramatically improving our ability to record earthquakes. Science , this issue p. [486][2] [1]: pending:yes [2]: /lookup/doi/10.1126/science.aat4458

This paper indicates the enhanced method of producing components of textile machines. The use of Nd-YAG laser beam in the manufacturing process improves quality of the components. The bottom rollers are one of the few important parts of textile machine giving quality yarns. The objective is to harden the complex shaped bottom roller and to eliminate post processes like grinding, bend removing followed by transportations and thereby made to run concentrically and giving quality yarn. The traditional processes of flame hardening, gas carburizing, nitriding, and induction hardening partially fulfil the requirements of hardness parameters on the roller. The laser hardening process was performed with 3 axes CNC machine attached with fiber optic laser head and servo controlled rotary chuck and suitable fixtures. The results of laser surface hardening show improved hardness, microstructure and uniform case depth on all contours and very less warping. The laser treated roller subjected to the normal working conditions on a textile machine run with almost concentric for longer life with which the yarn quality can be improved.