Author

# N. Chattrapiban

Bio: N. Chattrapiban is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Physics & Laser beam quality. The author has an hindex of 3, co-authored 6 publications receiving 228 citations.

##### Papers

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TL;DR: The characteristics of a singularity in a nondiffracting Bessel beam is explored experimentally by use of a programmable spatial light modulator with 64-level phase holograms and the diffraction efficiency is greatly improved.

Abstract: A laser beam with phase singularities is an interesting object to study in optics and may have important applications in guiding atoms and molecules. We explore the characteristics of a singularity in a nondiffracting Bessel beam experimentally by use of a programmable spatial light modulator with 64-level phase holograms. The diffraction efficiency with 64-level phase holograms is greatly improved in comparison with that obtained with a binary grating. The experiments show that the size and deflection angle of the beam can be controlled in real time. The observations are in agreement with scalar diffraction theory.

241 citations

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TL;DR: In this article, the uniformity, quality, and suitability of these patterns as elements for atom optics (e.g., atom-tunnel beam splitters) have been studied as a function of the phase quantization level and spatial resolution of phase mask.

Abstract: Two-dimensional spatial light modulators have been employed to create static and dynamic phase masks for embedding multiple vortices and exotic intensity-void structures in laser beams. A variety of patterns of singularities, producing dark longitudinal and transverse intensity channels, have been created. The uniformity, quality, and suitability of these patterns as elements for atom optics (e.g., atom-tunnel beam splitters) have been studied as a function of the phase quantization level and spatial resolution of the phase mask. Specifically, we show that (1) high-quality modes, those that propagate long distances and can be focused, can be generated when the number of phase steps between 0 and 2pi on the phase mask exceed four and (2) atom confinement increases with the charge of the vortex.

26 citations

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TL;DR: In this paper, a tunnel lock is introduced to divide, delay, and alter the direction of traveling clouds of cold atoms, which can be used to divide a single cloud into smaller clouds with distinct momentum.

Abstract: We introduce a tunnel lock that can be exploited to divide, delay, and alter the direction of traveling clouds of cold atoms. This versatile free-space element is implemented by crossing two atom tunnels formed by low-intensity, blue-detuned dark-hollow (Bessel mode) laser beams. We show that clouds of cold Rb atoms initially moving within one tunnel can be transferred to the other without heating by gating the intensities of the two tunnels--a tunnel lock--with an efficiency limited by the overlap volume. The element also can be used to divide a single cloud into smaller clouds, each having a distinct momentum.

3 citations

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TL;DR: An easy-to-setup experiment designed to measure the period and air drag coefficients of a damped pendulum is reported in this article , where the setup is made up of a solid metal ball and cylindrical shells of various sizes to create air drag.

Abstract: An easy-to-setup experiment designed to measure the period and air drag coefficients of a damped pendulum is reported. The setup is made up of a solid metal ball and cylindrical shells of various sizes to create air drag. An ultrasonic position sensor (HC-SR04) and an Arduino Uno board were located beneath the pendulum’s lowest position. The pendulum was released from a fixed height at a small initial angle. The periods of the oscillations involving different cylindrical shells were obtained from the time series plots of the pendulum’s position when the pendulum moves back and forth above the sensor. The drag coefficients were measured from five different values of string length. The coefficient was proportional to the size of the cylindrical shells and in agreement with the drag equation for a small Reynolds number.

1 citations

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13 Sep 2007TL;DR: In this paper, a simple model is presented that accounts for longitudinal acceleration and shows that a cloud confined in a tunnel with a potential having a Bessel mode distribution will absorb fewer photons than it would be trapped in a comparable tunnel with Laguerre-Gaussian mode distribution.

Abstract: The longitudinal and transverse evolution of thermal clouds have been studied
experimentally and theoretically in blue-detuned hollow tunnels. Tunnels based
on axicon generation and holographic phase-mask generation have been
investigated. A simple model is presented that (1) accounts for longitudinal
acceleration and (2) shows that a cloud confined in a tunnel with a potential
having a Bessel mode distribution will absorb fewer photons than it would
confined in a comparable tunnel with a Laguerre-Gaussian mode distribution. The
longitudinal and transverse profiles are fit to analytical distributions
functions from which we extract transverse and longitudinal temperatures of the
cloud. We find the two temperatures to be very different, with the transverse
temperature being as much as five times colder. Finally, we studied the energy
level structure within a Bessel potential theoretically and found that
single-mode propagation is possible.

1 citations

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TL;DR: In this paper, the authors discuss the motivation and requirements for these recent experiments, including the underpinning mathematics, and discuss exciting new directions for single-molecule biophysics.

Abstract: Single-molecule biophysics has transformed our understanding of biology, but also of the physics of life. More exotic than simple soft matter, biomatter lives far from thermal equilibrium, covering multiple lengths from the nanoscale of single molecules to up to several orders of magnitude higher in cells, tissues and organisms. Biomolecules are often characterized by underlying instability: multiple metastable free energy states exist, separated by levels of just a few multiples of the thermal energy scale k B T, where k B is the Boltzmann constant and T absolute temperature, implying complex inter-conversion kinetics in the relatively hot, wet environment of active biological matter. A key benefit of single-molecule biophysics techniques is their ability to probe heterogeneity of free energy states across a molecular population, too challenging in general for conventional ensemble average approaches. Parallel developments in experimental and computational techniques have catalysed the birth of multiplexed, correlative techniques to tackle previously intractable biological questions. Experimentally, progress has been driven by improvements in sensitivity and speed of detectors, and the stability and efficiency of light sources, probes and microfluidics. We discuss the motivation and requirements for these recent experiments, including the underpinning mathematics. These methods are broadly divided into tools which detect molecules and those which manipulate them. For the former we discuss the progress of super-resolution microscopy, transformative for addressing many longstanding questions in the life sciences, and for the latter we include progress in 'force spectroscopy' techniques that mechanically perturb molecules. We also consider in silico progress of single-molecule computational physics, and how simulation and experimentation may be drawn together to give a more complete understanding. Increasingly, combinatorial techniques are now used, including correlative atomic force microscopy and fluorescence imaging, to probe questions closer to native physiological behaviour. We identify the trade-offs, limitations and applications of these techniques, and discuss exciting new directions.

155 citations

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TL;DR: In this paper, Turunen and Friberg dealt with a class of fields with propagation-invariant properties such as the optical intensity distribution and applied them to scalar and electromagnetic approaches.

Abstract: The first article by Turunen and Friberg deals with a class of fields with propagation-invariant properties such as the optical intensity distribution. Coherent and partially coherent stationary and pulsed solutions are treated in view of scalar and electromagnetic approaches. Approximations of ideal propagation-invariant fields and methods for their generation are discussed. Finally, some application areas are covered.

149 citations

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TL;DR: This work describes the programmable spatial beam shaping of 100-kHz, 4-microJ amplified femtosecond pulses in a focal plane by wave-front modulation and obtains top-hat, doughnut, square, and triangle shapes of 20-microm size.

Abstract: We describe the programmable spatial beam shaping of 100-kHz, 4-?J amplified femtosecond pulses in a focal plane by wave-front modulation. Phase distributions are determined by a numerical iterative procedure. A nonpixelated optically addressed liquid-crystal light valve is used as a programmable wave-front tailoring device. Top-hat, doughnut, square, and triangle shapes of 20-?m size are obtained in a focal plane. Their suitability for femtosecond laser machining is demonstrated.

148 citations

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TL;DR: Helico-conical optical beams, different from higher-order Bessel beams, are generated with a parallel-aligned nematic liquid crystal spatial light modulator by multiplying helical and conical phase functions leading to a nonseparable radial and azimuthal phase dependence.

Abstract: Helico-conical optical beams, different from higher-order Bessel beams, are generated with a parallel-aligned nematic liquid crystal spatial light modulator (SLM) by multiplying helical and conical phase functions leading to a nonseparable radial and azimuthal phase dependence. The intensity distributions of the focused beams are explored in two- and three-dimensions. In contrast to the ring shape formed by a focused optical vortex, a helico-conical beam produces a spiral intensity distribution at the focal plane. Simple scaling relationships are found between observed spiral geometry and initial phase distributions. Observations near the focal plane further reveal a cork-screw intensity distribution around the propagation axis. These light distributions, and variations upon them, may find use for optical trapping and manipulation of mesoscopic particles.

100 citations

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TL;DR: This paper elucidates through both theory and experiment the behavior of silica microspheres moving under the influence of the periodic optical field provided by a Bessel beam, and compares two different computational models based on Mie scattering and geometrical ray optics to find good qualitative agreement.

Abstract: Spatially periodic optical fields can be used to sort dielectric microscopic particles as a function of size, shape or refractive index. In this paper we elucidate through both theory and experiment the behavior of silica microspheres moving under the influence of the periodic optical field provided by a Bessel beam. We compare two different computational models, one based on Mie scattering, the other on geometrical ray optics and find good qualitative agreement, with both models predicting the existence of distinct size-dependent phases of particle behavior. We verify these predictions by providing experimental observations of the individual behavioral phases.

89 citations