Laser-induced plasma formation in water with up to 400 mJ double-pulse LIBS

Double-pulse LIBS is a promising technique for deep-sea applications.LIBS measurements in shallow water with up to 400 mJ each pulse were done to select laser parameters which promote optimized spectral line emission from plasma even at elevated pressures,where line broadening until loss of most of the spectral information can occur.Optical emission spectroscopy,using a Czerny-Turner spectrometer,has been applied to investigate the dependence of the emitted radiation on laser parameters and hydrostatic pressure.It has been found,that higher laser pulse energies,especially with short pulse delay as required in high water pressure,can also have an adverse effect on the measured spectrum.

Localized bursting of mesocarp cells triggers catastrophic fruit cracking

The so-called rain-cracking of sweet cherry fruit severely threatens commercial production.Simple observation tells us that cuticular microcracking(invisible)always precedes skin macrocracking(visible).The objective here was to investigate how a macrocrack develops.Incubating detached sweet cherry fruit in deionized water induces microcracking.Incubating fruit in D2O and concurrent magnetic resonance imaging demonstrates that water penetration occurs only(principally)through the microcracks,with nondetectable amounts penetrating the intact cuticle.Optical coherence tomography of detached,whole fruit incubated in deionized water,allowed generation of virtual cross-sections through the zone of a developing macrocrack.Outer mesocarp cell volume increased before macrocracks developed but increased at a markedly higher rate thereafter.Little change in mesocarp cell volume occurred in a control zone distant from the crack.As water incubation continued,the cell volume in the crack zone decreased,indicating leaking/bursting of individual mesocarp cells.As incubation continued still longer,the crack propagated between cells both to form a long,deep macrocrack.Outer mesocarp cell turgor did not differ significantly before and after incubation between fruit with or without macrocracks;nor between cells within the crack zone and those in a control zone distant from the macrocrack.The cumulative frequency distribution of the logtransformed turgor pressure of a population of outer mesocarp cells reveals all cell turgor data followed a normal distribution.The results demonstrate that microcracks develop into macrocracks following the volume increase of a few outer mesocarp cells and is soon accompanied by cell bursting.

Spatial heterogeneity of flesh-cell osmotic potential in sweet cherry affects partitioning of absorbed water

A fleshy fruit is commonly assumed to resemble a thin-walled pressure vessel containing a homogenous carbohydrate solution.Using sweet cherry(Prunus avium L.)as a model system,we investigate how local differences in cell water potential affect H2O and D2O(heavy water)partitioning.The partitioning of H2O and D2O was mapped nondestructively using magnetic resonance imaging(MRI).The change in size of mesocarp cells due to water movement was monitored by optical coherence tomography(OCT,non-destructive).Osmotic potential was mapped using microosmometry(destructive).Virtual sections through the fruit revealed that the H2O distribution followed a net pattern in the outer mesocarp and a radial pattern in the inner mesocarp.These patterns align with the disposition of the vascular bundles.D2O uptake through the skin paralleled the acropetal gradient in cell osmotic potential gradient(from less negative to more negative).Cells in the vicinity of a vascular bundle were of more negative osmotic potential than cells more distant from a vascular bundle.OCT revealed net H2O uptake was the result of some cells loosing volume and other cells increasing volume.H2O and D2O partitioning following uptake is non-uniform and related to the spatial heterogeneity in the osmotic potential of mesocarp cells.

Waterproof coatings for high-power laser cavities

With the ever-increasing laser power and repetition rate,thermal control of laser media is becoming increasingly important.Except for widely used air cooling or a bonded heat sink,water cooling of a laser medium is more effective in removing waste heat.However,how to protect deliquescent laser media from water erosion is a challenging issue.Here,novel waterproof coatings were proposed to shield Nd:Glass from water erosion.After clarifying the dependence of the waterproof property of single layers on their microstructures and pore characteristics,nanocomposites that dope SiO_(2) in HfO_(2) were synthesized using an ion-assisted co-evaporation process to solve the issue of a lack of a highindex material that simultaneously has a dense amorphous microstructure and wide bandgap.Hf_(0.7)Si_(0.3)O_(2)/SiO_(2) multifunctional coatings were finally shown to possess an excellent waterproof property,high laser-induced damage threshold(LIDT)and good spectral performance,which can be used as the enabling components for thermal control in high-power laser cavities.

High-aspect 3D two-photon polymerization structuring with widened objective working range (WOW-2PP)

We developed a novel two-photon polymerization(2PP)configuration for fabrication of high-aspect three-dimensional(3D)structures,with an overall height larger than working distance of the microscope objective used for laser beam focusing into a photosensitive material.This method is based on a modified optical 2PP setup,where a microscope objective(1003 high N.A.),immersion oil and cover glass can be moved together into the photosensitive material,resulting in an effective higher and wider objective working range(WOW-2PP).The proposed technique enables the fabrication of high-aspect structures with sub-micrometer process resolution.3D structures with a height of 7 mm are demonstrated,which could hardly be built with the conventional 2PP set-up due to refractive index mismatch and laser beam disturbances.

UV-LED projection photolithography for high-resolution functional photonic components

The advancement of micro-and nanostructuring techniques in optics is driven by the demand for continuous miniaturization and the high geometrical accuracy of photonic devices and integrated systems.Here,UV-LED projection photolithography is demonstrated as a simple and low-cost approach for rapid generation of two-dimensional optical micro-and nanostructures with high resolution and accuracy using standard optics only.The developed system enables the projection of structure patterns onto a substrate with 1000-fold demagnification.Photonic devices,e.g.,waveguides and microring resonators,on rigid or flexible substrates with varied geometrical complexity and overall structure dimensions from the nanometer to centimeter scale were successfully prepared.In particular,high-resolution gratings with feature sizes down to 150 nm and periods as small as 400 nm were realized for the first time by this approach.Waveguides made of doped laser active materials were fabricated,and their spontaneous emission was detected.The demonstrated superior performance of the developed approach may find wide applications in photonics,plasmonics,and optical materials science,among others.

Simple route toward efficient frequency conversion for generation of fully coherent supercontinua in the mid-IR and UV range

Fiber supercontinua represent light sources of pivotal importance for a wide range of applications,ranging from optical communications to frequency metrology.Although spectra encompassing more than three octaves can be produced,the applicability of such spectra is strongly hampered due to coherence degradation during spectral broadening.Assuming pulse parameters at the cutting edge of currently available laser technology,we demonstrate the possibility of strongly coherent supercontinuum generation.In a fiber with two zero-dispersion wavelengths a higher-order soliton experiences a temporal breakdown,without any compression or splitting behavior,which leads to nearly complete conversion of input solitonic radiation into resonant nonsolitonic radiation in the dispersive wave regime.As the process is completely deterministic and shows little sensitivity to input noise,the resulting pulses appear to be compressible down to the sub-cycle level and may thus hold a new opportunity for direct generation of attosecond pulses in the visible to near ultraviolet wavelength range.

Spatial separation effects in a guiding procedure in a modified ion-beam-sputtering process

In the present state of the art,ion beam sputtering is used to produce low-loss dielectric optics.During the manufacturing of a dielectric layer stack,the deposition material must be changed,which requires rapid mechanical movement of vacuum components.These mechanical components can be regarded as a risk factor for contamination during the coating process,which limits the quality of high-end laser components.To minimize the particle contamination,we present a novel deposition concept that does not require movable components to change the coating material during the coating process.A magnetic field guiding technique has been developed,which enables the tuning of the refractive index in the layer structure by sputtering mixtures with varying compositions of two materials using a single-ion source.The versatility of this new concept is demonstrated for a highreflection mirror.

Overseas offices: a new attempt to disseminate Light

Light:Science&Applications(LSA)has established itself as a leading resource for the optics and photonics community within only four and a half years.In 2016,LSA received its third impact factor of 13.6,being listed as second among 90 journals in optics,according to the 2015 Journal Citation Reports from Thomson Reuters.In 2015,LSA published 70 papers,increased by 30%compared with 2014,and the total citations rose by 65%.In 2016,LSA received more than 700 papers from 35 countries and regions and published 84 papers,with a steady increase in submissions and publications over the years.The long-term goal of LSA is to become an outstanding international journal in optics and photonics.We are approaching this step by step.However,we know that there is a long way ahead of us,and the efforts of several generations may be needed to achieve it.We are willing to exert our greatest efforts in this direction.We have been implementing various measures to enhance the quality and improve the impact of LSA.Today,a new attempt to set up LSA overseas offices is starting.Overseas offices will be based in local regions,covering neighboring areas,to perform activities relevant to LSA.The main responsibilities of overseas offices will include undertaking some of the manuscript processing workload to expedite the procedure,attending academic conferences relevant to optics,visiting outstanding scientists and leading research groups,hosting Light overseas forums,inviting high-quality papers,promoting LSA,etc.

xtraction of internal phase motions in femtosecond soliton molecules using an orbital-angular-momentum-resolved method

Internal motions in femtosecond soliton molecules provide insight into universal collective dynamics in various nonlinear systems.Here we introduce an orbital-angular-momentum(OAM)-resolved method that maps the relative phase motion within a femtosecond soliton molecule into the rotational movement of the interferometric beam profile of two optical vortices.By this means,long-term relative phase evolutions of doublet and triplet soliton molecules generated in an all-polarization-maintaining mode-locked Er-fiber laser are revealed.This simple and practical OAM-resolved method represents a promising way to directly visualize the complex phase dynamics in a diversity of multisoliton structures.

Advanced control and modeling of deposition processes

During the last decade, striking improvements could be achieved for the precise control of deposition processes in optical coating technology. For example, as a consequence of enormous progresses in measure- ment and computer technology, direct optical monitoring in a broad spectral range can be considered as a common tool in many production environments nowadays. Besides the development of the corresponding hardware and measurement channels, advanced approaches for the evaluation of the acquired data and new multiple sensor monitoring strategies moved into the focus of modern research on the way towards de- terministic deposition techniques. In this context, also innovative concepts for the simulation of deposition processes to forecast the result for a specified coating design and automatic online correction algorithms gained of importance to reduce the risk of failure in coating production. The present contribution will be dedicated to selected aspects in this field, especially addressing broad band optical monitoring systems. A short review on examples for existing hardware configurations and software tools will be presented illus- trating the advantages of modern process control techniques. Novel approaches based on the modeling of thin film growth are discussed as an additional strategy to improve the predictability of coating processes.