Numerical Aperture Objective Lens Research Articles

Direct observation of a pure focused evanescent field of a high numerical aperture objective lens by scanning near-field optical microscopy

Intensity distributions of a tightly focused evanescent field generated by a center blocked high numerical aperture (1.65) objective lens are investigated by a scanning near-field optical microscope. The pure focused evanescent field is mapped and a splitting phenomenon of the focal spot along the direction of polarization, caused by depolarization, is observed not only on the interface, where the evanescent field is generated, but also in the parallel planes away from the interface. The decaying nature of the focused evanescent field shows good agreement with the theoretical predication, indicating that the field is purely evanescent and does not contain a significant contribution from the propagating component. It is found in our experiment that the light coupling efficiencies of the longitudinal polarization component Ez and the transverse polarization component Ex to the fiber probe differ by a factor of 3.

Anomalous phenomenon of a focused evanescent Laguerre-Gaussian beam

We demonstrate theoretically and experimentally an anomaly in the intensity distribution at the focal region of a Laguerre-Gaussian beam, when such a beam is focused by a high numerical aperture objective lens through an index-mismatched interface satisfying the total internal reflection condition. An asymmetric rotation of the focal field arising from the interplay of the phase shift induced by the total internal reflection and the helical phase of the Laguerre-Gaussian beam has been experimentally observed by a scanning near-field optical microscope. A cross-section analysis shows that the experimental results match well with the theoretical predictions.

Read/Write Mechanism for a Scattered Type Super-Resolution Near-Field Structure Using an AgOx Mask Layer and the Smallest Mark Reproduced

A working mechanism for a scattered type super-resolution near-field structure (super-RENS) disk using a silver oxide (AgOx) mask layer has been studied experimentally. The AgOx mask layer has five possible states depending on the laser power: AgOx (as-depo), uniformly dispersed Ag particles (after the initialization of 3.5 mW), Ag cluster (4–5 mW), Ag diffusion (5.5–7.5 mW), and a Ag ring structure (greater than 8 mW) for an objective lens numerical aperture of 0.5, a laser wavelength of 826 nm and a medium velocity of 2 m/s. On the other hand, the GeSbTe recording layer has the following possible states: crystal, halfway amorphous, completely amorphous, and gas bubble associated with Ag particles. For super-resolution read power (4 mW), the mask layer will have a Ag ring structure that increases both the signal carrier to noise ratio and the resolution limit. We improve the resolution limit of 413 nm to 50 nm at the duty ratio of 10% for the write optical pulse.

Detection and characterization of longitudinal field for tip-enhanced Raman spectroscopy

We characterized the longitudinal field formed at a tightly focused spot by a high numerical aperture objective lens using a tip-enhanced near-field microscope. The longitudinal field efficiently excites the localized surface plasmon polaritons at the metallic tip apex resulting in an electric field enhancement. Radially polarized light generated by a combination of four half-waveplates successfully increases the longitudinal field resulting in higher sensitivity for tip-enhanced Raman spectroscopy of adenine nanocrystals.

Write-Once Disk with BiFeO Thin Films for Multilevel Optical Recording

We found out that small marks are formed without large deformation and intersymbol interference (ISI) on a BiFeO thin film. Therefore, a BiFeO write-once disk is suitable for multilevel optical recording. We confirmed that our write-once disk realizes a recording capacity of 23 GB using a laser diode with a 405 nm wavelength and a 0.65 numerical aperture objective lens.

Glass cutting by femtosecond pulsed irradiation

We report on quartz and glass cutting by a lateral scanning of femtosecond pulses (150 fs at 1 kHz repetition rate) of 800 nm wavelength at room and low pressure (5 Torr) air ambience. Pulses were focused by a low numerical aperture (NA0.1) objective lens. Optimization of fabrication conditions: pulse energy and scanning speed were carried out to achieve large-scale (millimeter-to-centimeter) cutting free of microcracks of submicron dimensions along the edges and walls of the cut. Cutting through out the samples of 0.1-0.5 mm thickness was successfully achieved without apparent heat affected zone. At low air pressure (5 Torr) ambience, redeposition of ablated material was considerably reduced. It is demonstrated that the damage on the rear surface was induced by the stress waves, which originated from the plasma ablation pressure pulse. The mechanism of femtosecond-laser cutting of transparent materials at high irradiance and the influence of stress waves generated by plasma plume are discussed.

Integrated MEMS optical flying head with lens positioning actuator for small form factor optical data storage

An integrated and miniaturized optical flying head (OFH) is presented for a small form factor with high-density portable optical data storage. It is composed of a high numerical aperture (NA) objective lens, a microlens actuator for adjusting the position of the objective lens, an integrated air-bearing-slider (ABS), and an embedded magnetic-field-modulation (MFM) coil for magneto-optical recording. To adjust the optimal focal length of the lens, a parallel-plate vertical actuator is adopted. In addition, the area-optimized torsion type H-shape spring is used for vertical actuation. The glass ABS structure and the double metal layer MFM coil are fabricated on a transparent substrate, bonded to the silicon actuator. The overall size of the integrated OFH, assembled with the high numerical aperture (NA=0.85) objective lens, is 3 mm×1.6 mm×0.5 mm (length×width×thickness), which makes it small enough to be furnished in a portable optical data storage device. A prototype of small optical drive is also developed to satisfy the form factor of PCMCIA type II. The prototype includes the integrated and miniaturized OFH and the basic operation of the drive is tested.

Scanning total internal reflection fluorescence microscopy under one-photon and two-photon excitation: image formation.

We propose a new type of total internal reflection fluorescence microscopy (TIRFM) called scanning TIRFM (STIRFM) that uses a focused ring-beam illumination and a high-numerical-aperture objective (NA = 1.65). The evanescent field produced by the STIRFM is focused laterally, producing a small excitation volume that can induce a nonlinear effect such as two-photon absorption. Experimental images of CdSe quantum dot nanocrystals and Rhodamine 6G-doped microbeads show that good lateral and axial resolutions are achieved with the current setup. The theoretical simulation of the focal spot produced in STIRFM geometry shows that the focused evanescent field is split into two peaks because of the depolarization effect of a high numerical-aperture objective lens. However, the point-spread function analysis of both one-photon and two-photon excitation cases shows that the detection of the focus-splitting effect is dependent on the detection pinhole size. The effect of pinhole size on image formation is theoretically investigated and confirmed experimentally with the nanocrystal images.

Evaluation of spherical particle sizes with an asymmetric illumination microscope

A polarized microscope system is used to perform goniometric measurements of light scattered by small particles. The light incident angle on a sample of monodispersed latex microspheres is increased sequentially and a microscope objective lens collects scattered light from the samples. Light is only collected at angles greater than the objective lens numerical aperture (NA) so that only light scattered by the spheres is collected. The experimental results were modeled with a Mie theory-based algorithm. Experiments conducted with microspheres of diameter 1.03, 2.03, and 6.4 /spl mu/m show that, by decreasing the objective lens NA from NA=0.55 to NA=0.0548, a more distinguishable scattering pattern is detectable. From these highly shaped curves, we found that the size of a sphere of nominal diameter 2.03 /spl mu/m was 2.11 /spl plusmn/0.06 /spl mu/m and a 6.4 /spl mu/m sphere was 6.34 /spl plusmn/0.07 /spl mu/m.

System Aspects of Dual-Layer Phase-Change Recording with High Numerical Aperture Optics and Blue Laser

In this publication, key technologies for blue laser recording and dual layer phase-change disks with a total capacity of 50 Gbytes are explained and system margins are evaluated. Key challenges are the phase-change recording layer design, a robust read and write system with low intrinsic noise and the optical pickup design including, e.g., high numerical aperture (NA) objective lens, spherical aberration compensation devices and beam shaping optics. Blue-laser dual-layer technology will be emerging as the next-generation optical data storage standard beyond compact discs (CDs) and digital versatile discs (DVDs).

Dual Layer Phase Change Optical Disk Using Limit Equalizer

A simple manufacturing process of multilayer recording disks has been developed to fabricate a large-capacity optical disk of more than 40 GB, using a short-wavelength laser diode and high numerical aperture (NA) objective lens. Some existing production facilities for the digital versatile discs (DVD) are applicable to this process. These disks can be utilized for long-time video recording of high-definition TV broadcasting. We have developed a dual-layer rewritable optical disk with capacity of more than 43 GB per one side of a 120 mm disk by this process. We obtained good performance of playback jitter for disks of 43 GB and 46.6 GB capacities with on-groove recording and limit equalizer at a user data transfer rate of 36 Mbps as well as good direct overwriting characteristics over 1,000 cycles.

Inorganic Recordable Disk with More Eco-Friendly Material for Blue

We realized an inorganic write-once disk using a high numerical aperture (NA) objective lens and a blue-violet laser diode. Its recording layer was Bi–Ge nitride alloy which was more environmentally friendly than that of the rewritable disk. The data-to-clock jitter of 5.7% was obtained at 25 GB capacity, using the limit equalizer. In addition, we confirmed that this disk had potential for application as a 1X-2X recordable disk.

Design of Domain Wall Displacement Detection Disk with Groove Recording for High Density and Wide Recording Power Tolerance

Domain wall displacement detection (DWDD) magneto-optical (MO) recording is the most useful method for achieving high linear density recording without using a higher numerical aperture (NA) objective lenses. Securing a wide recording power tolerance is very important to realize a high density optical storage system. From this point of view, we designed the DWDD disk with groove recording using blue laser and NA 0.60 optics. We optimized the heat sink structure and the displacement layer for groove recording, and we could improve the bit error rate with a track pitch of 0.44 µm and a high linear density of 0.07 µm/bit, which corresponds to 21 Gbit/inch2. Additionally, we developed groove substrates using reactive ion etching (RIE) and O2 plasma treatment. We found that the land shape was very important for the recording power tolerance, and we could obtain a wide recording power tolerance with a bit length of 0.09 µm. We confirmed that we could achieve higher density by using a narrower track pitch while maintaining sufficient recording power tolerance.

Direct measurement of laser power through a high numerical aperture oil immersion objective lens using a solid immersion lens

For many laser applications, information on irradiated laser power is important. However, direct measurement of laser power through a high numerical aperture objective lens is difficult in a laser microscope. In this article, we propose a method which use a solid immersion lens (SIL) for such measurements. A laser beam focused by an objective lens is introduced to the flat surface of a SIL, emitted through the spherical surface, and then detected. In this way the divergence of the laser beam is reduced, and as a result the detection efficiency of the laser power increases. From theoretical analysis, a Weierstrass-sphere type SIL was found to be an appropriate thickness for this propose. Transmittance of the SIL is evaluated for several refractive indeces. The validity of this method is confirmed experimentally.

Reflections on colourful ommatidia of butterfly eyes.

The eye shine of butterflies from a large number of ommatidia was observed with a modified epi-illumination apparatus equipped with an objective lens of large numerical aperture. A few representative cases are presented: the satyrine Bicyclus anynana, the heliconian Heliconius melpomene, the small white Pieris rapae and the small copper Lycaena phlaeas. The colour of the eye shine is determined mainly by the reflectance spectrum of the tapetal mirror and the transmittance spectrum of the photoreceptor screening pigments, if present near the light-guiding rhabdom. Reflectance spectra measured from individual ommatidia show that tapetum and screening pigments are co-expressed in fixed combinations, thus determining different ommatidial classes. The classes are distributed in an irregular pattern that can be rapidly assessed with the novel epi-illumination apparatus. Many butterfly species appear to have red-reflecting ommatidia, which is interpreted to indicate the presence of red-sensitive photoreceptors.

Development of Recording Stacks for a Rewritable Dual-Layer Optical Disc

In this paper results are presented on the development of recording layers for a rewritable dual-layer phase-change optical disc. The disc is based on the digital video recording (DVR) system utilising a blue laser and a high numerical-aperture objective lens. With such a disc the capacity of the DVR system could be increased to about 45 GB. Various stack designs, write strategies and recording characteristics of the media are discussed. For each recording layer a design with a fairly good performance is found.

Optical Pick-up for Blue Optical Recording at NA = 0.85

Sony and Philips have recently developed the basic technology for a 22.5 GB optical recording system, based on a blue laser (#x03BB; = 405 nm) and high numerical aperture (NA = 0.85) objective lens. This system is referred to by the acronym DVR (for Digital Video Recording). In this paper we describe the relization of a compact optical pickup unit capable of writing and reading data on disc according to the DVR format.

High-Density Rewritable Optical Disk Using Groove Recording

For an optical disk system using an objective lens of numerical aperture (NA) 0.7 and a GaN laser, the performances of the groove-recording scheme were investigated. A disk having 17 GB capacity showed the initial jitter of 11.9% with an equalizer for digital versatile disks (DVD). With an adaptive equalizer and a Viterbi decoder, sufficiently low bit error rates and wide tilt margins were obtained.

Jitter Analysis for Land/Groove Phase Change Disk

A 22 GB optical video recording system with an objective lens of high numerical aperture (NA), a blue laser and a thin cover layer is proposed. We classify the jitter which increased by aberrations into three components for this system. We analyze the dependence of jitter components on the groove depth in detail. Furthermore, we confirm advantages of the limit equalizer (Limit-EQ) and the two-dimensional adaptive equalizer for the land/groove (L/G) phase change disk.

Radial and Tangential Tilt Detection for Rewritable Optical Disks

In an optical disk system which uses a short wavelength laser diode and a high numerical aperture objective lens, it is necessary to detect and compensate for the disk tilt, because the coma aberration deteriorates the read/write characteristics and the tilt margin becomes narrower. This paper presents a new radial and tangential tilt detection method for rewritable optical disks, which is based on the intensity distribution of the reflected light from the disk. This method features high sensitivity (about 0.37/° for radial direction and about 0.51/° for tangential direction) and is suitable for high-frequency servo operation. Moreover, it can be combined with the differential push-pull detection method and the land/groove detection method by using three beams. Experimental results have demonstrated the validity of this method.