Radiation filters and emitters for the NIR based on periodically structured metal surfaces

Abstract

The spectrally selective optical properties of wavelength selective radiation emitters and filters based on periodically microstructured metal surfaces were investigated. Metal surfaces were structured by the use of a holographic mask and subsequent etching processes. Due to the microstructure, thermally excited surface plasmons couple to electromagnetic radiation. Therefore a structured tungsten surface can act as a selective radiation emitter. The calculation of the absorptance by a rigorous diffraction theory allows the prediction of the emissivity of such structures. The angle dependent emissivity of tungsten gratings with periods of 1.4 μm and 2.0 μm was measured. A peak emissivity of 70% at a wavelength of 1.6 μm was achieved. Band pass filters for the near infrared spectral range based on perforated metal films were investigated theoretically and experimentally. Filters with a grating period of 2.0 μm were produced. A peak transmittance of 80% at a wavelength 2.9 μm was achieved. The optical properties of the diffractive elements described partly show a strong angle dependence     

Suppression of higher diffraction orders in the extreme ultraviolet with a trapezoidal nano-mirror array

ABSTRACT

Higher diffraction orders from a grating introduce harmonic contamination in ‘monochromatic’ output beams processed by grating monochromators at synchrotron radiation facilities, resulting in imprecise calibration of optical elements and detectors. Suppressing these orders can be achieved with a quasi-random nano-hole array, but its fabrication can be a significant limiting factor for implementation. Here, an advanced type of grating is demonstrated that contains a periodic array of several hundred million trapezoidal nano-mirrors with a grazing-incidence reflection geometry that suppresses higher diffraction orders. Moreover, it reduces the difficulty of fabrication to the level of a traditional grating. It has great potential for harmonic suppression in synchrotron radiation, spectral diagnostics of plasmas, and astrophysics.     

Erratum

Abstract

Results of a photon scanning tunnelling microscopy study of the plane diffraction grating with nickel stripes on a quartz substrate are reported. The ripples in the optical images with period of 600 nm have been observed when the plane of incidence of laser beam was perpendicular to the grooves of the grating. The interference patterns for the propagating modes in far field have been detected. They are supposed to be the result of Mie scattering of evanescent wave by the elements of the diffraction grating.     

Analysis and Performance of 2·7 μm Er3+ Fibre Laser Amplifiers and Oscillators

Abstract

A mathematical model is described which estimates the performance of erbium doped fibre lasers and amplifiers at 1·5 μm or at 2·7 μm. The model has shown good agreement with experimental results and has been used to optimize the configuration of new systems. Continuous wave laser action has been demonstrated at λ = 2·7 μm in an Er³⁺ doped multi-mode fluorozirconate fibre laser, pumped by an 800 nm laser diode.     

Fabrication of a concentric-circular focusing grating coupler by a conic-wave-front interference method and light-convergence experiments using the coupler

An interference method utilizing conic-wave-front light for the fabrication of a concentric-circular and chirped grating is proposed. The design method and fabrication of an interference lens that generates conic-wave-front light are also shown. A focusing element is constructed from a concentric-circular grating coupler with a 0.4-mm diameter and a concentric-circular focusing grating coupler with an annular aperture of 2-mm focal length and 2.0-4.0-mm diameter. Light-convergence experiments using the focusing element were able to obtain a focusing spot of 0.5 μm × 0.7 μm at half-intensity widths for a wavelength of 820 nm in combination with liquid-crystal polarization elements.     

Shift and shape of grating diffracted beams

Abstract

The grating diffraction of beams is theoretically investigated by applying an electromagnetic method (the Integral Equation System Method with Parametrization of the grating profile = IESMP) to their plane wave components. For the first time, explicit values for the displacement of grating diffracted Gaussian beams are calculated with this method. For total reflection this displacement of beams is known as the Goos-Hänchen shift. A maximum shift of 36 μm has been found for the investigated sinusoidal grating near an anomaly which is much greater than the known Goos–Hänchen shift of about 1 μm for the total reflection case. The replacement of the angular spectrum of plane waves with constant wavelength by a wavelength spectrum of plane waves of constant direction allows an analogous treatment of short-time pulses. Surprisingly, the above anomaly causes a maximum temporal shift of 80 fs for the pulse diffraction. These temporal shifts and additional effects like pulse deformations can influence ultra short-time pulse experiments. Furthermore, the behaviour of temporally and spatially Gaussian shaped light pulses (TSG pulses) by grating diffraction are studied considering the diffraction of an angular and wavelength dependent spectrum of plane waves. The diffraction of a short TSG pulse at the above grating deforms the pulse and creates an additional smaller satellite pulse. All described effects occur only at positions of the space–time complex filtering function in the angular-wavelength frequency space with high gradient of the phase.     

Stable 4 W CW solid-state green source pumped by fibre-coupled diode-laser arrays

Abstract

A high-power Nd:YAG laser end-pumped by a fibre-coupled diode-laser array system is described. When operated at 1 μm, the device produced 10 W of output power in the TEM₀₀ transverse mode with a slope efficiency of 43%. The system was operated using both 600 μm and 400 μm core, 0·37 N.A. multimode fibres for delivery of the pump radiation, and also with Nd:YVO₄ as the gain material. By intracavity doubling with KTP, 4 W of non-chaotic two-mode 0·5 μm output was obtained.     

Computation of the near-field pattern with the coupled-wave method for transverse magnetic polarization

Abstract

In this paper, an accurate method for computing the elecromagnetic field distribution in lamellar gratings is proposed. The method that relies on the rigorous coupled-wave analysis provides accurate numerical results and avoids possible sources of artefacts due to permittivity discontinuities. Its performance is analysed through various lamellar grating cases, including dielectric and metallic materials, the visible and near-infrared (1–10 μm) regions of the spectrum. Special attention is placed on field singularities which are in general present at the grating wedges for transverse magnetic polarization.     

PET polymer ablation using excimer laser for nozzle plate application

Abstract

Polyethylene terephthalate (PET) film drilling using a 248 nm excimer laser through photomask projection is presented. The parameter effects of laser fluence, shot number and repetition rate on the processing results are examined. A high quality microhole array with 50 μm thick PET film is fabricated. When the projection process is carried out, the diameter differences in the microhole in the front and back side of PET are observed. This causes a conical shape in the kerf. The formation of this conical shape in terms of the laser process parameters is discussed. The process parameter effects are investigated and characterised to improve the PET microhole laser machining quality.     

An Ytterbium-doped Monomode Fibre Laser: Broadly Tunable Operation from 1·010 μm to 1·162 μm and Three-level Operation at 974 Nm

Abstract

Continuous-wave laser action has been observed from an ytterbium-doped monomode fibre laser on the three-level transition at 974 nm and on the four-level transition at 1036 nm with slope efficiencies of 67% and 77% respectively, with respect to absorbed power. Tuning behaviour is described, in which polarisation control by means of fibre loops has allowed smooth continuous tuning from 1·010 μm to 1·162 μm.     

Diffraction Grating Characterization Via the Excitation of Surface Plasmons

Abstract

A diffraction grating has been manufactured in silica using interferometry and then replicated into perspex. Both grating profiles have then been characterized by fitting theory to experimentally obtained surface plasmon resonances excited on the grating surfaces after they had been coated with silver. The groove profile in the silica grating is distorted from purely sinusoidal. This distortion is very well characterized using the second-order surface plasmon and is described in this study a simple one-parameter model. The validity of the model is confirmed by similar examination of the surface plasmon resonances from the replica which is found to have the almost exactly the opposite distortion.     

High-power external-cavity AlGaAs/GaAs/InGaAs quantum-dimensional heterolasers (λ = 1.06 μm)

Use of an external cavity with a grating ensures effective narrowing of the linewidth (～0.35 nm) of a high-power multimode semiconductor laser with a broad (100 μm) stripe contact. An output power of up to 550 mW has been reached with experimental external-grating-cavity laser diodes. It is demonstrated that a 3-mm-long multimode laser diode based on a quantum-dimensional AlGaAs/GaAs/InGaAs heterostructure (λ = 1.06 μm) can be used with a directly pumped PPLN crystal waveguide to obtain second-harmonic radiation with λ = 0.532 μm.     

基于AFM氮化硅探针刻蚀方法制作聚碳酸酯纳米光栅

基于原子力显微镜(AFM)探针的纳米机械刻蚀技术以其成本低、分辨率高的优势被广泛应用于各种纳米元器件的制造中.为了得到最优的光栅结构,首先通过单次刻蚀实验定量分析了刻蚀方向、加载力和刻蚀速率等3个主要加工参数对所得纳米沟槽形貌和尺寸的影响,给出了普通氮化硅探针对聚碳酸酯(PC)的加工特性及加工效率.然后通过改变沟槽间距(100~500 nm)得到了不同周期的纳米光栅结构,并确定了这种探针与样品的组合对间距的要求及最佳加工参数:沿垂直于微悬臂长轴向右刻蚀,加载力2.3μN,刻蚀速率2.6μm/s.最后利用该技术对实验室已有原子光刻技术所得周期为213 nm的一维Cr原子光栅结构进行了复制加工,得到了均匀的213 nm一维光栅,证明这种基于AFM探针的纳米机械刻蚀技术可被广泛应用于纳米加工.     

Diffractive optical element used in an external feedback configuration to tune the wavelength of uncoated Fabry-Pérot diode lasers

Abstract

A diffractive optical element (DOE) has been designed, fabricated and used in an external feedback configuration to set the wavelength of operation of uncoated Fabry-Pérot diode lasers. The DOE was designed to replace the conventional elements of an external feedback system, which are a collimating lens and grating in the Littrow configuration. The goal was to simplify use of the external cavity laser by replacing the lens and grating with a single optical element while maintaining the performance that is achieved with a grating and lens. Four DOEs were fabricated with two different focal lengths and two different reflectivities. DOE external cavity lasers were tested for maximum tunable range and stability of the wavelength of operation and compared with an external cavity laser based on a lens and grating in the Littrow configuration. A 40 nm tuning range was achieved with the DOE external cavity laser and this is comparable with the tuning range of the external cavity lasers based on a grating and collimating lens in the Littrow configuration.     

Reversible and irreversible index gratings in a NPP-doped low-Tg polymer composite

Abstract

A reversible photorefractive grating and an irreversible local photo-induced aggregation grating were observed in a low glass transition temperature polymer composite poly(N-vinylcarbazole): 2,4,7-trinitro-9-fluroenone: N-ethylcarbazol: N-(4-nitrophenyl)-(l)-prolinol. Two gratings were distinguished by using the two-beam coupling (TBC) experiment and the four-wave mixing experiment. For photorefractive grating, the TBC coefficient was measured to be 140 cm^?1 at an applied electric field of E₀ = 85V/μm, corresponding to a photorefractive grating of 3.6 × 10^?3. The photo-induced aggregation grating was measured to be about 7 × 10^?3.     

Thermoelectric La-doped SrTiO3 epitaxial layers with single-crystal quality: from nano to micrometers

Abstract

High-quality thermoelectric La_0.2Sr_0.8TiO₃ (LSTO) films, with thicknesses ranging from 20 nm to 0.7 μm, have been epitaxially grown on SrTiO₃(001) substrates by enhanced solid-source oxide molecular-beam epitaxy. All films are atomically flat (with rms roughness < 0.2 nm), with low mosaicity (<0.1°), and present very low electrical resistivity (<5 × 10^?4 Ω cm at room temperature), one order of magnitude lower than standard commercial Nb-doped SrTiO₃ single-crystalline substrate. The conservation of transport properties within this thickness range has been confirmed by thermoelectric measurements where Seebeck coefficients of approximately –60 μV/K have been recorded for all films. These LSTO films can be integrated on Si for non-volatile memory structures or opto-microelectronic devices, functioning as transparent conductors or thermoelectric elements.     

Femtosecond laser pulse propagation in a uniaxial crystal

Abstract

The wave equation describing the vector propagation of a femtosecond laser pulse of a few optical cycles in a uniaxial crystal is solved numerically by the method of unidirectional waves. Propagation of the pulse in the direction normal to the optical axis is studied, taking into account both second- and third-order nonlinearities of the crystal. Conversion efficiency as a function of crystal length, pump intensity and pulse duration is studied. As an example, the propagation of femtosecond laser pulse of τ = 10 fs duration at λ = 810 nm in a LiNbO₃ crystal 12 μm thick is studied numerically.     

Holographic self-amplification in amorphous As-Se semiconductor films

Abstract

Holographic self-amplification in amorphous As₅₅Se₄₅ and As₆₅Se₃₅ films has been studied. Results on this amplification over a wide range of initial diffraction efficiencies 10^?5% < η₀ < 1% are reported. The degree of amplification increases with decreasing η₀. At fixed values of η₀ and of the sample thickness, the maximum self-amplification corresponds to a period A = 2·0 μm of the grating hologram. An increase in the diffraction efficiency in the dark has been observed for the first time in As-Se films.     

Femtosecond optical parametric oscillators based on periodically poled lithium niobate

Abstract

We describe two configurations of collinearly pumped femtosecond optical parametric oscillator based on periodically poled lithium niobate and tunable in the infrared from 975 nm to 4.98 μm. Maximum output powers of 240 mW for the signal and 106 mW for the idler were recorded with 25 mW of average power measured at 4.88 μm. An overall conversion efficiency of 35% and slope efficiencies for the signal of 46% at a wavelength of 1.04 μm and 70% at 1.1 μm were measured. Interferometric autocorrelations of the signal and idler pulses at various wavelengths within the tuning range have been obtained and imply nearly transform-limited pulse durations of about 140fs for the signal and about 190fs for the idler.     

Structured light spots projected by a Dammann grating with high power efficiency and uniformity for optical sorting

We report a method for microfluidic multiple trapping and continuous sorting of microparticles using an optical potential landscape projected by a Dammann grating, enabling a high power-efficient approach to forming a composite two-dimensional spots array with high uniformity. The Dammann grating is fabricated in a photoresist by optical lithography. It is employed to create an optical lattice for multiple optical trapping and sorting in a mixture of polymer particles (n = 1.59) and silica particles (n = 1.42) with the same diameters of 3.1 μm. In addition to the exponential selectivity by the projected optical landscapes, the proposed microfluidic sorting system has advantages in terms of high power efficiency and high uniformity due to the Dammann grating.