In-system optimization of a hologram for high-stability parallel laser processing.

A method for optimizing a computer-generated hologram (CGH) for high-stability laser processing is proposed. The CGH is optimized during laser processing; therefore, unpredicted dynamic changes in the laser processing system, in addition to its static imperfections, are automatically compensated for by exploiting the rewritable capability of the spatial light modulator. Consequently, the short-term and long-term stability are improved, which will contribute to the realization of high-speed, high-precision laser processing. A CGH that generated 36 parallel beams was continuously optimized, and the maximum uniformity reached 0.98, which is higher than reported in previous research. To the best of our knowledge, this is the first demonstration of gradual improvement of parallel laser processing with in-process optimization of the CGH. Furthermore, it was also demonstrated that the performance of the laser processing system against unexpected disturbances was improved.

Aberration-resistible topological charge determination of annular-shaped optical vortex beams using Shack-Hartmann wavefront sensor.

Determining topological charge (TC) of optical vortex (OV) beams is important for many applications, such as optical measurement and information transmission through long-distance propagation. In this application, the OV beams usually have an annular intensity profile at the receiving end and are inevitably distorted by aberrations during propagation. In this paper, we propose a simple, direct, and aberration-resistible method to determine the TC value of this annular-shaped OV beam with a Shack-Hartmann wavefront sensor (SH-WFS). Our approach involves finding a closed-path along the annular intensity distribution ridge, and then determining the TC value by a discrete circulation calculation with only the phase-slope vectors along the closed-path. Verification experiments were performed using a phase-only spatial light modulator to generate OV beams and aberrations, while SH-WFS to measure the intensity profile and phase-slopes. The results show that our method can determine the TC value of up to ± 20. The robustness against wavefront aberration and simulated atmospheric turbulence was evaluated. We also verified the proposed closed-path's superiority to other circular closed-paths for TC determination.

Measurement of spontaneous blinks in patients with Parkinson's disease using a new high-speed blink analysis system.

INTRODUCTION: Parkinson's disease (PD) patients often have a blinking abnormality. In this study, we examined the kinematic features of spontaneous blinking in 65 PD patients and 62 healthy controls by a new research method utilizing an intelligent vision sensor camera prototype with a 1kHz sampling rate. METHODS: Spontaneous blinks were measured by use of a non-stress 'intelligent vision sensor' camera prototype. RESULTS: The mean spontaneous blink rate was 17.9 (blinks/min) in the PD patients and 15.6 in the controls (no correlation). However, there were extremely low and extremely high blink-rate groups among the PD patients. The amplitude of the closing and opening phase in the PD patients were significantly smaller than those in the controls. Small blink waves (100-200msec) prior to blink onset existed in 60% of the PD patients and in 18% of the controls. CONCLUSION: During spontaneous blinking the blink amplitude is decreased, and the pause between the closing and opening phase is prolonged in patients with PD. Small blink waves prior to blink onset were also characteristically found in the PD patients.

Massively parallel femtosecond laser processing.

Massively parallel femtosecond laser processing with more than 1000 beams was demonstrated. Parallel beams were generated by a computer-generated hologram (CGH) displayed on a spatial light modulator (SLM). The key to this technique is to optimize the CGH in the laser processing system using a scheme called in-system optimization. It was analytically demonstrated that the number of beams is determined by the horizontal number of pixels in the SLM NSLM that is imaged at the pupil plane of an objective lens and a distance parameter pd obtained by dividing the distance between adjacent beams by the diffraction-limited beam diameter. A performance limitation of parallel laser processing in our system was estimated at NSLM of 250 and pd of 7.0. Based on these parameters, the maximum number of beams in a hexagonal close-packed structure was calculated to be 1189 by using an analytical equation.

Implicit Memory in Monkeys: Development of a Delay Eyeblink Conditioning System with Parallel Electromyographic and High-Speed Video Measurements.

Delay eyeblink conditioning, a cerebellum-dependent learning paradigm, has been applied to various mammalian species but not yet to monkeys. We therefore developed an accurate measuring system that we believe is the first system suitable for delay eyeblink conditioning in a monkey species (Macaca mulatta). Monkey eyeblinking was simultaneously monitored by orbicularis oculi electromyographic (OO-EMG) measurements and a high-speed camera-based tracking system built around a 1-kHz CMOS image sensor. A 1-kHz tone was the conditioned stimulus (CS), while an air puff (0.02 MPa) was the unconditioned stimulus. EMG analysis showed that the monkeys exhibited a conditioned response (CR) incidence of more than 60% of trials during the 5-day acquisition phase and an extinguished CR during the 2-day extinction phase. The camera system yielded similar results. Hence, we conclude that both methods are effective in evaluating monkey eyeblink conditioning. This system incorporating two different measuring principles enabled us to elucidate the relationship between the actual presence of eyelid closure and OO-EMG activity. An interesting finding permitted by the new system was that the monkeys frequently exhibited obvious CRs even when they produced visible facial signs of drowsiness or microsleep. Indeed, the probability of observing a CR in a given trial was not influenced by whether the monkeys closed their eyelids just before CS onset, suggesting that this memory could be expressed independently of wakefulness. This work presents a novel system for cognitive assessment in monkeys that will be useful for elucidating the neural mechanisms of implicit learning in nonhuman primates.

High-order optical vortex position detection using a Shack-Hartmann wavefront sensor.

Optical vortex (OV) beams have null-intensity singular points, and the intensities in the region surrounding the singular point are quite low. This low intensity region influences the position detection accuracy of phase singular point, especially for high-order OV beam. In this paper, we propose a new method for solving this problem, called the phase-slope-combining correlation matching method. A Shack-Hartmann wavefront sensor (SH-WFS) is used to measure phase slope vectors at lenslet positions of the SH-WFS. Several phase slope vectors are combined into one to reduce the influence of low-intensity regions around the singular point, and the combined phase slope vectors are used to determine the OV position with the aid of correlation matching with a pre-calculated database. Experimental results showed that the proposed method works with high accuracy, even when detecting an OV beam with a topological charge larger than six. The estimated precision was about 0.15 in units of lenslet size when detecting an OV beam with a topological charge of up to 20.

Stable and flexible multiple spot pattern generation using LCOS spatial light modulator.

The LCOS spatial light modulator (LCOS-SLM) can generate desired multiple spot patterns (MSPs) via the application of suitable computer-generated-holograms (CGHs), but the MSP intensity distribution varies because ambient temperature affects the phase modulation characteristic and causes wavefront distortion. To generate high-optical-quality MSPs we use our hardware-compensated (with a Peltier system to even out phase modulation) and software-corrected (via multiplication of the CGH by temperature correction coefficients) LCOS-SLMs. Experimental results with a 14 × 14 MSP generation show that the hardware-compensated LCOS-SLM provides stable MSPs between 9 to 32 °C. The software-corrected LCOS-SLM provides uniform spots over twice the temperature range obtained with conventional SLM method. We confirm that our methods are highly efficient for use in two-photon excitation microscopy application such as multifocal mulitphoton microscopy.

Self-distortion compensation of spatial light modulator under temperature-varying conditions.

Conventional methods of compensating for self-distortion in liquid-crystal-on-silicon spatial light modulators (LCOS-SLM) are based on aberration correction, where the wavefront of the incident beam is modulated to compensate for aberrations caused by the imperfect optical flatness of the LCOS-SLM surface. However, the phase distribution of an LCOS-SLM varies with changes in ambient temperature and requires additional correction. We report a novel phase compensation method under temperature-varying conditions based on an orthonormal Legendre series expansion of the phase distribution. We investigated the temperature dependency by controlling the ambient temperature with an incubator and successfully corrected for self-distortion in a temperature range of 20 °C to 50 °C. Our approach has the potential to be adopted in tight-focusing applications which require wavefront modulation with very high accuracy.

Effects of dielectric planar interface on tight focusing coherent beam: direct comparison between observations and vectorial calculation of lateral focal patterns.

We report direct observation of lateral focal patterns through an acrylic material to investigate the effects of aberrations caused by a planar dielectric interface. Numerical analyses based on vectorial Huygens-Fresnel diffraction theory were also performed to examine the behavior of three-dimensional point spread functions. Experimental and numerical results showed agreement of the behavior of the peak position in the focal patterns with changes in the interface position. Our approach has the potential to predict the effects of aberrations in confocal laser scanning microscopes and super-resolution applications.

Correlation matching method for high-precision position detection of optical vortex using Shack-Hartmann wavefront sensor.

We propose a new method for realizing high-spatial-resolution detection of singularity points in optical vortex beams. The method uses a Shack-Hartmann wavefront sensor (SHWS) to record a Hartmanngram. A map of evaluation values related to phase slope is then calculated from the Hartmanngram. The position of an optical vortex is determined by comparing the map with reference maps that are calculated from numerically created spiral phases having various positions. Optical experiments were carried out to verify the method. We displayed various spiral phase distribution patterns on a phase-only spatial light modulator and measured the resulting singularity point using the proposed method. The results showed good linearity in detecting the position of singularity points. The RMS error of the measured position of the singularity point was approximately 0.056, in units normalized to the lens size of the lenslet array used in the SHWS.

[Measurement of age-related changes in human blinks using a high-speed blink analysis system].

PURPOSE: To measure the spontaneous and voluntary blinks of both younger and older people using a new device that simplifies the detailed recording of eye blinking. METHODS: Fifty healthy volunteers (10 women and 15 men under 40 years of age, range: 22-38 years, and 20 women and 5 men above 60 years of age, range: 63-85 years) were examined after obtaining informed consent from each subject. Eyelid movements of all subjects were recorded using a high-speed blink analysis system. The spontaneous eye-blinks of the subjects were recorded during sessions consisting of a 40 seconds' period following which the subjects were instructed to blink as rapidly as possible for 5 seconds in which the blinks were again recorded. The upper lid position and movement data were plotted every millisecond by processing the recorded images. RESULTS: The frequency of the spontaneous blinks did not differ between the younger and older subjects. The women tended to blink more frequently in both age groups. The average amplitude and duration time of the spontaneous blinks in the younger subjects were greater than those in the older subjects. Voluntary blinks in the younger subjects were more frequent than in the older subjects. Women tended to make deeper and faster voluntary blinks. CONCLUSION: Whereas the frequency of the voluntary blinks differed between the younger and older subjects, that of the spontaneous blinks did not differ. The findings of this study also revealed the gender-related differences in spontaneous and voluntary blinks.

High-quality generation of a multispot pattern using a spatial light modulator with adaptive feedback.

We propose and demonstrate high-quality generation of a uniform multispot pattern (MSP) by using a spatial light modulator with adaptive feedback. The method iteratively updates a computer generated hologram (CGH) using correction coefficients to improve the intensity distribution of the generated MSP in the optical system. Thanks to a simple method of determining the correction coefficients, the computational cost for optimizing the CGH is low, while maintaining high uniformity of the generated MSP. We demonstrate the generation of a 28×28 square-aligned MSP with high uniformity. Additionally, the proposed method could generate an MSP with a gradually varying intensity profile, as well as a uniform MSP consisting of more than 1000 spots arranged in an arbitrary pattern.

Fast frequency-resolved terahertz imaging.

We propose a fast, frequency-resolved, real-time, terahertz imaging method. With our method, images at two specific terahertz frequencies can be acquired in 1 min. Three kinds of drugs (L-histidine, maltose, and CBZ3), which have absorption peaks in the terahertz region, were distinguished in 3 min by using our method. This technique can be used in industrial applications, such as nondestructive testing.

Sidelobe reduction of tightly focused radially higher-order Laguerre-Gaussian beams using annular masks.

We report the reduction of sidelobes in tight focusing patterns of radially higher-order Laguerre-Gaussian (LG) beams with nonhelical phase structures. Numerical calculations based on the vectorial Debye theory reveal that a class of annular masks reduces sidelobes in the tight focusing patterns only for radially even-order LG beams. The present scheme produces small focal spots beyond the diffraction limit suitable for application to scanning microscopy, laser fine processing, etc.

[Measurement of spontaneous blinks with a high-speed blink analyzing system].

PURPOSE: In order to analyze spontaneous blink kinematics easily and circumstantially, we developed a new method using an intelligent vision system (IVS) camera with a 1 KHz sampling rate, and evaluated the efficacy of this system. METHOD: Eleven healthy male volunteers were examined after obtaining informed consent. Eyelid movements in the primary eye position were recorded with an IVS camera twice, for 30 seconds each. Data of upper lid position and lid movement were plotted every 1 msec by image processing of the recorded images. Thereafter blink duration and maximum blink velocity in every spontaneous blink were calculated. RESULTS: Thirty-nine instances of complete lid-closure type and seventy of incomplete lid-closure type of spontaneous blinks were observed. The average duration of the down-phase, the up-phase, and the total blink were the same for both types; about 100 msec., 220 msec., and 320 msec. respectively. The average down-phase maximum velocity was about 180 mm/sec. in complete lid-closures and 120 mm/sec. in incomplete lid-closures. The average up-phase maximum velocity was about 60 mm/sec. in complete lid-closures and 45 mm/sec. in incomplete lid-closures. Blink amplitude and the maximum velocity achieved during lid closing and opening were strongly correlated and exhibited a linear relationship (r = 0.85, r = 0.73 p < 0.0001). CONCLUSION: This new, non-invasive system is an easy to use measuring method for blink kinematics and is highly reliable and very useful.

Terahertz movie of internal transmission imaging.

Recently terahertz imaging using two-dimensional E-O sampling has attracted much interest because it can acquire real-time terahertz images unlike a conventional raster scan method. We are applying this technique to the non-destructive measurement of opaque materials in a visible range. We acquired 10-fps consecutive terahertz transmission images: dripping water in a plastic pipe and metal included in a piece of gum. Since the obtained images were confirmed to be proportional to the electric field of the terahertz waves, the images in the present paper are useful for quantitative analysis. We also showed the signal-to-noise ratio of the terahertz images.