Double Exposure Method Research Articles

Complementary layer pairs of plasmonic ladder-like structured films: Fabrication and visible-near-infrared properties

Complementary layer pairs consisting of an array of elongated gold patches on one layer with the complementary elongated holes on a second separated gold layer were fabricated by laser interference lithography using a double-exposure method. The anisotropic complementary layers, with a stretched hexagonal lattice, show polarization dependent enhanced transmittance at near-infrared wavelengths. The wavelengths of the peak transmittance through the plasmonic films are well correlated with the wavelengths of the resonant excitations of surface plasmon resonances of the system. The enhanced transmittance through such complementary layer pairs and the role played by the plasmonic resonances at the wavelengths with peak transmittance are confirmed through electromagnetic simulations. The enhanced transmittance is mediated by the plasmonic resonances of the hole arrays or cavity resonances due to the pair of complementary layers.

Polarization-controlled images based on double-exposure polarization holography in an azobenzene liquid-crystalline polymer.

Polarization-controlled optical image operations were demonstrated based on the double-exposure polarization holographic method. Two images were stored in the same volume of an azobenzene liquid-crystalline polymer by recording superimposed holograms, a pair of polarization gratings with one spatial frequency, using two orthogonal circularly polarized 532nm beams and were reconstructed with a 650nm laser. The recorded polarization holographic gratings were investigated to show distinctive polarization selectivity, high diffraction efficiency, and good stability. The brightness and the polarization of the diffracted images were found to be dependent on the polarization of the readout beam, and two images could be reconstructed individually or simultaneously.

Laser-assisted nanostructuring of Silicon in liquid environment

Formation of surface nanostructures on a Silicon target immersed into liquids is experimentally studied under its ablation by femtosecond laser pulses. Nanotexturing of Silicon upon its exposure to delayed femtosecond pulses and double exposure method is investigated. Two different types of morphological features are observed, namely periodic ripples and nanostructures. Field emission scanning electron microscopy shows that the density of nanostructures as well as their morphology depends on such parameters as fluence and the delay time between pulses and reaches its maximum at delay of 1 ps. Two-dimensional homogenous array of nanostructures is formed by laser ablation in liquids using double-exposure method. Possible applications of generated nanostructures are discussed.

Review of resist-based flare measurement methods for extreme ultraviolet lithography

Flare (stray light) is an important effect impacting extreme ultraviolet lithography (EUVL) imaging system performance. Four flare measurement methods including Kirk, modulation transfer function, double exposure, and zonal ring approximation method are reviewed and analyzed theoretically. The point spread function of an EUV NXE:3100 exposure tool is extracted from the measured Kirk flare (KF) and fitted with a double-fractal model. The KF for this NXE:3100 tool is determined to be 8.5% for a 2-μm diameter absorber pad placed in a 12-mm outer radius bright field, which is larger than the previous 5% KF data measured by ASML and IMEC in 2011. The observation of the increased flare level in the NXE:3100 tool suggests that contamination of EUV optics may be a potential problem for EUVL manufacturing.

Study on Object Slight Displacement Measure Using Digital Image Hologram Method

Digital image hologram and double exposure method is used to measure displacement of an object in this paper, the intensity of object light has been increased effectively, the contrast of interference fringes has been improved, clear interference fringes has been gotten. A new method has been proposed that CCD and EALCD are applied in order to record the digital hologram and interference fringes, the drawback is avoided successfully that fixing, relocation and nonlinear recording of traditional hologram recording material are. Better experimental effect is achieved.

SEM characterization of two-dimensional patterns generated in titanium by femtosecond laser interferometry

Laser ablation using ultrafast femtosecond lasers and holographic schemes has proven to be a powerful and versatile tool for surface and volume structuring. The principle of operation of this technique is simple: when two or more pulses overlap in time and space, an interference pattern is generated that can be used to create periodic surface structures. In addition, due to the extremely short pulse duration, a very high peak power is achieved leading to intense non-linear effects. As a result, almost any type of material can be processed without undesirable collateral thermal effects.In this paper, characterization of two-dimensional (2D) patterns generated in titanium using femtosecond laser radiation has been carried out using scanning electron microscopy (SEM). The laser source is a commercial Yb:KYW laser system providing pulses with a duration of 560 fs at a central wavelength of >= 1030 nm. The surface topography was characterized using a Hitachi S2400 scanning electron microscope operated at an electron acceleration voltage of 25.0 kV. Laser processing was performed in air on polished grade 2 titanium samples, a material typically used in low load bearing medical devices.One-dimensional (1D) gratings were created using a modified Michelson interferometer described in detail elsewhere (Oliveira et al., 2012). To create 2D gratings a double exposure method was used. First, 1D gratings were produced in linear tracks by translating the sample relatively to the stationary interfering laser beams with a fixed scanning velocity of 0.1 mm/s. As an example, Figure 1 depicts SEM pictures of horizontal and vertical 1D gratings with period of about 3.9 m, generated using a pulse energy and pulse repetition rate of 0.35 mJ and 100 Hz, respectively. The peak to valley distance of these patterns can be controlled either by changing the scanning velocity or the pulse repetition rate. By overlapping two linear tracks, different kinds of 2D structures can be created. Figure 2 depicts a square pattern obtained by overlapping two 1D gratings rotated by 90°. The dimensions of the squares depend on the one-dimensional gratings period, which in turn can be easily controlled by varying the distance between the interfering beams. Figure 3 depicts two other possibilities: i) trapezium-like patterns obtained by rotating the 1D gratings by 45°, and ii) rectangular patterns obtained using 1D gratings with different periods and rotated by 90°.The proposed optical setup offers a simple method of texturing the surface of materials and, hence, to control surface properties such as wettability. In the case of titanium, this is particularly important because surface texturing enhances its osseointegration ability. For this purpose, when compared with the columns spontaneously formed on titanium surfaces treated with femtosecond laser radiation, these 2D gratings present the major advantage of being size and shape-controllable.

“Double Exposure Method”: a Novel Photolithographic Process to Fabricate Flexible Organic Field-Effect Transistors and Circuits

A novel process called "double exposure method" has for the first time been developed to utilize common organic materials as insulating layers at low annealing temperature in the process of photolithography. In this method, organic dielectric layer will not dissolve in the final lift-off step by using developer to replace traditional acetone. Bottom-gate bottom-contact (BGBC) OFETs are fabricated on the flexible PET substrates with polystyrene (PS) and pentacene as dielectric layer and semiconductor layer, respectively. Transistors with mobility of 0.36 cm2 V(-1) s(-1) and logic inverter with gain of 9 on the plastic substrates have been fabricated, demonstrating the potential appliction of "double exposure method" in flexible organic electronics.

Visible range lasing in dye-doped doubly periodic layered structures in dichromate gelatin emulsions

We have fabricated dye-doped doubly periodic layered structures exhibiting multiple bandgaps in the visible range in dichromate gelatin emulsions by a double-exposure holographic interference method. More importantly, optically pumped lasing with higher efficiency and lower threshold compared to that of singly periodic layered structures was observed in the dye-doped doubly periodic gelatin samples. This efficient lasing could be explained by the enhancement of the density of states at the overlapping bandgaps of two singly periodic layered structures.

Double-exposure phase calculation method in electronic speckle pattern interferometry based on holographic object illumination

Multiple-exposure phase calculation procedures are widely used in electronic speckle pattern interferometry to calculate phase maps of displacements. We developed a double-exposure process based on holographic illumination of the object and the idea of the spatial carrier phase-shifting method to examine transient displacements. In our work, computer-generated holograms and a spatial light modulator were used to generate proper coherent illuminating masks. In this adjustment all phase-shifted states were at our disposal from one recorded speckle image for phase calculation. This technique can be used in the large scale of transient measurements. In this paper we illustrate the principle through several examples.

Axis-Selective Photo-Fries Rearrangement and Photoinduced Molecular Reorientation in Liquid Crystalline Polymer Films

The thermally enhanced photoinduced molecular reorientation based on an axis-selective photo-Fries rearrangement was explored for the first time using three liquid crystalline polymethacrylates with 4-(2′-(4″-methoxyphenyl)ethynyl)phenyl benzoate side groups (1a), 4-methoxybiphenyl benzoate side groups (1b), and 4-methoxyphenyl benzoate side groups (1c). All the polymeric films exhibited an axis-selective formation of the photo-Fries products at the phenyl benzoate derivatives side groups by irradiating with linearly polarized (LP) UV light. Annealing the films in the liquid crystalline temperature range of the material greatly amplified the photoinduced small optical anisotropy of the irradiated films. For 1a and 1b, the photoinduced small anisotropy was amplified in a direction parallel to the polarization (E) of LPUV light and the reorientational order (S) was greater than 0.7. In contrast, the orientation direction was perpendicular to E for 1c (S ∼ 0.57). Finally, a simple double-exposure method usin...

Dual-wavelength distributed feedback fiber laser based on double exposure and equivalent phase shift method

A special sampling structure based on double exposure technology is proposed to achieve dual-wavelength lasing in the distributed feedback fiber laser. This structure is composed of two grating pitches in one sampling period, which could be realized by changing the fiber's length in the fabrication. Through employing an equivalent phase shift, only a submicrometer-level precision is required for precise phase control. Then a stable dual-wavelength laser with the spacing of 400 pm is obtained in the experiment successfully. The output power is 30.46 μW and the sidemode suppression ratio is 46 dB under a pumped power of 146 mW.

On the localization of plastic strain under compression of LiF crystals

The plastic flow localization patterns for alkali halide LiF crystals under compression have been investigated. The main spatiotemporal regularities of the strain localization at different stages of deformation hardening in the single crystals have been established. The relation has been traced between the orientation of localized strain zones and the crystallography of slip systems of the test specimens studied simultaneously by the double-exposure speckle photography and photoelasticity methods.

J0503-2-3 ディーゼル噴霧構造の時空間計測への展開([J0503-2]多次元計測技術の展開と応用(2))

For the reduction of diesel engine emissions, it is significant to clarify the spray atomization and formation processes. In this investigation, a detailed observation of fuel droplets characteristic was made by applying a double exposure method using a color film, a light fiber and a wavelength converter to a previous measurement technique. The photographic system is composed of a specialized lens system, and enables to measure the whole spray shape and fuel droplets characteristics at an instant. The light source is the second harmonic, and the third harmonic of Nd:YAG laser. This technique enables the spray measurement of the chronological order. In addition, it is expected new knowledge about a spray atomization mechanism be obtained.

Thermo-mechanical characterization of surface-micromachined microheaters using in-line digital holography

This paper describes the application of lensless in-line digital holographic microscopy (DHM) to carry out thermo-mechanical characterization of microheaters fabricated through PolyMUMPs three-layer polysilicon surface micromachining process and subjected to a high thermal load. The mechanical deformation of the microheaters on the electrothermal excitation due to thermal stress is analyzed. The numerically reconstructed holographic images of the microheaters clearly indicate the regions under high stress. A double-exposure method has been used to obtain the quantitative measurements of the deformations, from the phase analysis of the hologram fringes. The measured deformations correlate well with the theoretical values predicted by a thermo-mechanical analytical model. The results show that lensless in-line DHM with Fourier analysis is an effective method for evaluating the thermo-mechanical characteristics of MEMS components.

Phase aberration compensation of digital holographic microscopy based on least squares surface fitting

Digital holographic microscopy allows the numerical reconstruction of the complex wavefront of samples, especially biological samples such as living cells. In digital holographic microscopy, a microscope objective is introduced to improve the transverse resolution of the sample; however a phase aberration in the object wavefront is also brought along, which will affect the phase distribution of the reconstructed image. We propose here a numerical method to compensate for the phase aberration of thin transparent objects with a single hologram. The least squares surface fitting with points number less than the matrix of the original hologram is performed on the unwrapped phase distribution to remove the unwanted wavefront curvature. The proposed method is demonstrated with the samples of the cicada wings and epidermal cells of garlic, and the experimental results are consistent with that of the double exposure method.

An experimental study on the distribution of the drop size and velocity in asymmetric impinging jet sprays

Distributions of the drop size and velocity in an asymmetric impinging jet are investigated by injecting water and a sodium carbonate (Na2CO3) solution, which simulates the mixing process in impinging jet sprays of liquid oxidizer and liquid fuel for liquid propellants. The liquid sheet formed from the impinging jet is visualized and the drop size distributions are obtained by using image processing for the visualized images. The drop size distribution of the asymmetric impinging jets is fitted to the Rosin-Rammler distribution function. The obtained drop size distributions according to the azimuth angle in the impinging jet are compared with the theoretical predictions of previous research. The experimental results of the drop size distributions are located between the two curves obtained from the theoretical predictions by treating each jet in the asymmetric impinging jets as an independent wall-impinging jet. PIV images using a double-exposure method were processed to obtain the drop velocity vector in the impinging jets. Whether the drops shedding from the edge of the asymmetric impinging jets occurs radially or tangentially is also investigated from the PIV results.

Speckle Noise Reduction in Vibration Measurement by Time-Average Speckle Interferometry and Digital Holography-a Unifying Approach

Time-average electronic speckle pattern interferometry and digital holography are two representative full-field coherent optical techniques used in mechanical vibration measurement. In both techniques, the quantitative data processing is affected by several difficulties. The most important are the weak contrast of Bessel-type fringes and the speckle noise. The greatest obstacle in achieving complete amplitude field estimation comes from the orthogonal components of time-averaged digital holograms or speckle interferograms, where multiplicative, high-frequency phase noise covers the deterministic, vibration-related phase. Several researchers studied these problems in relation with the double-exposure method. In the present paper, the author presents in a single, unifying approach, these double-exposure methods, common to speckle interferometry and digital holography. An important reduction of multiplicative high-frequency phase noise allows obtaining fringe-averaged patterns whose intensity noise is much lower than in classical time-average holography. The analysis allows choosing the most appropriate method leading not only to a higher fringe pattern quality, lower noise and extended measurement range, but also to a method of vibration-related phase estimation, which may include in some stages subpixel precision. The method, based on the mathematical inversion of the Bessel function on monotonic intervals, is equivalent to phase unwrapping, but it only uses time-averaged fringe patterns.

Fabrication of Photonic Crystals by Holographic Lithography Method

In this study, we found out the new fabrication process condition for Photonic crystals(PCs). PCs were fabricated by holographic lithography(HL), instead of commonly used electron beam lithography(EBL). HL process enable periodic large area fabrication of PCs. Also this method can easily control the pitch of periodic patterns. We set up holographic lithography system by laser and some optical components. The source of light used laser of 442 nm wavelength. Photo-resist(PR) used DMI-150 model. The viscosity of PR is diluted with propylene glycol monomethyl ether acetate(PGMEA) which is solvent for DMI-150. This experiment is holographic lithography of rotated double exposure method for PCs pattern. The method use only one beam. Result data is shown by atomic force microscope(AFM), scanning electron microscope(SEM) and 3D contour image. At the this study, we conclude conditions which we need periodic structure for PCs. It is some factor. For example, incident angle, exposure time, rotation angle, etc. And we show incident angle calculation recipe for needed size of periodic patterns. We already manufacture PCs structure design and simulation tool. Nano structure of this paper’s result is applied to designed PCs patterns.

Realization of dot- and antidot-type two-dimensional photonic crystals by double holographic method

Two-dimensional photonic crystals (2D PCs) were fabricated on a 1.18-μm-thick polymer resist (DMI-150) by a double-exposure holographic method using a HeCd laser with a wavelength of 442nm. The 2D PC arrays exhibited various primitive lattice structures from triangle to square according to the change of the rotation angle (γ) of the double-exposure beams. In addition, the period, filling factor, and form (dot or antidot) of the PCs could be controlled by the experimental conditions such as the incident interference angle (θ), the exposure power, and duration. The following exposure procedure was applied: first holographic exposure, followed by sample rotation, and finally, second holographic exposure. The first and second holographic exposures were carried out at a fixed angle (θ=11°) and the rotation was performed in the range of γ=45°–90°. The variation of diffraction efficiency (η) during the exposure process and after the development was monitored using a HeNe laser in real time. The images of the prepared 2D PCs were observed by scanning electron microscopy and atomic force microscopy, and the data on their reciprocal lattices were obtained by the diffracted patterns. We believe that the double holographic method is a suitable tool to realize the dot- and antidot-type 2D PCs with a periodic array of a large area.

Dynamic characterization of MEMS diaphragm using time averaged in-line digital holography

In this paper dynamic characterization of a MEMS diaphragm is investigated using lens-less time averaged in-line digital holography. The analysis and capability of the numerically reconstructed amplitude and phase information from in-line time averaged holograms as applied to MEMS vibration are presented. Particularly the effect of mean static state on the phase in time averaged digital holography is explored. A novel double exposure method is also demonstrated using a diverging object wave suitable for dynamic characterization of small size objects. A phase jump in the static deformation fringes in the vibrating regions is observed and described and can be used for precise analysis of vibration mode shape under simultaneous presence of mean static deformation. A simple and robust tool for dynamic optical metrology of MEMS devices and micro-objects using time averaged in-line digital holography is thus proposed.