Chandrasekhar Roychoudhuri
University of Connecticut
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Featured researches published by Chandrasekhar Roychoudhuri.
Optics Express | 2003
DongIk Lee; Chandrasekhar Roychoudhuri
When two electromagnetic fields of different frequencies are physically superposed, the linear superposition equation implies that the fields readjust themselves into a new mean frequency whose common amplitude undulates at half their difference frequency. Neither of these mathematical frequencies are measurable quantities. We present a set of experiments underscoring that optical fields do not interfere with each other or modify themselves into a new frequency even when they are physically superposed. The multi-frequency interference effects are manifest only in materials with broad absorption bands as their constituent diploes attempt to respond collectively and simultaneously to all the optical frequencies of the superposed fields. Interference is causal and real since the dipoles carry out the operation of summation dictated by their quantum mechanical properties.
Optical Engineering | 1994
Weiquin Chen; Chandrasekhar Roychoudhuri; Conrad M. Banas
Low-cost, efficient, and compact high-power laser diodes (LDs) will make desktop laser manufacturing (rapid prototyping, sintering, drilling, marking, etc.) a reality soon. Laser processing of materials requires not only high average power, from tens of watts to kilowatts, but also high incident beam intensity or power density, from 103 to 108 W/cm2. Current commercial high-power LDs do emit 108 W/cm2; however, they are microscopic in size, and an individual diode emits ~ 1 W (cw) in a highly divergent (~30 x 10 deg) multimode structure. Gathering high power from a large number of such microscopic incoherent diodes into a small spot of high intensity requires micro-optic component and complex system design. Several difterent design approaches for high-intensity laser-diode systems are presented. Some of these are commercial, others will be soon, and still others will need technological developments. Possible applications and some preliminary results of direct diode-laser sintering and transformation hardening of stainless-steel ribbons are also presented.
Journal of Nanophotonics | 2010
Chandrasekhar Roychoudhuri
Non-interaction of waves (NIW) in the linear domain is an unappreciated but general principle of nature. Explicit recognition of this NIW-principle will add renewed momentum to the progress of fundamental physics and related technologies like spectrometry, coherence, polarizations, laser mode-locking, etc. This principle helps us appreciate that the mathematical correctness of a theorem and its capability to predict certain groups of measured data, do not necessarily imply that the theorem is always capable of mapping real interaction processes in nature. The time-frequency Fourier theorem (TF-FT) is an example since superposed light beams, by themselves, cannot reorganize or sum their energies. Quantum Mechanics (QM) correctly discovered that photons (light beams) are non-interacting bosons. Yet, to accommodate (i) the classical belief that light beams interfere (interact) by themselves, and (ii) Einsteins heuristic hypothesis that discrete packets of energy emitted by molecules travel as indivisible quanta (contradicting spontaneous diffractive spreading), QM has been forced to hypothesize that a photon interferes only with itself. In reality, it is the quantized detecting material media that make the superposition effects become manifest as their physical transformations, from bound electrons to released photoelectrons, after absorbing energy from all the beams due to induced simultaneous stimulations by the beams.
Optical Science and Technology, the SPIE 49th Annual Meeting | 2004
Chandrasekhar Roychoudhuri
In reality, the duration of all light sources (oscillators) is finite. So, effectively, light is always pulsed, whether it is of nano second or of giga second durations. This paper develops a conceptually congruent model of propagating the carrier frequency of a generic pulse directly in the time domain through traditional instruments and media. The modeling approach covers all spectrometers like multi-beam Fabry-Perots and gratings, and two-beam Fourier transform spectrometers. The established approach uses a non-causal Fourier integral to generate Fourier decomposed frequencies of the pulse, which exist in all time, and find their steady state delays through instruments and media. This frequency domain approach gives correct results when appropriately used, but encounters contradictions under some situations that are discussed. In contrast, the time-domain analysis, while mathematically less elegant, always makes correct predictions, besides giving us a deeper and better understanding of the physical processes of temporal evolution of the pulse through various instruments.
Optics Express | 2003
David W. Young; Chandrasekhar Roychoudhuri
This paper presents a simulation technique developed to concurrently model the pump and laser power evolution in a cladding pumped rare-earth doped fiber. The simulation technique uses a series of scaling factors to dramatically decrease simulation run-times, while maintaining accuracy. This approach differs from previous methods in that it can simulate arbitrary pump cladding shapes. The results of the simulation are validated using a decagon-shaped cladding pumped, ytterbium doped fiber. Good correlation is found between the simulated and experimental pump evolution and conversion efficiency.
Active and passive optical components for WDM communications. Conference | 2003
Chandrasekhar Roychoudhuri; DongIk Lee; Yongyuan Jiang; Shigeo Kittaka; Masatoshi Nara; Vladimir V. Serikov; Masahiro Oikawa
High resolution DWDM devices based on the principles of gratings (planar, Bragg, AWG, etc.) and Fabry-Perots (etalon, Lummer-Gehrke plate, etc.) suffer from inherent limitations due to (i) temporal pulse stretching of data, and (ii) broadening of time integrated spectral (demuxed) fringes. While the relation, dνFdt >1, can account for these limitations, our analysis imply that dnF does not represent real, physical frequencies. We explain the broader implications of this interpretation in designing DWDM devices based on gratings and Fabry-Perots and illustrate how to use prisms, photonic crystals and non-linear devices for very high data rate per channel.
Journal of The Optical Society of America A-optics Image Science and Vision | 1998
James M. Anderson; Chandrasekhar Roychoudhuri
We provide a rigorous, closed-form mathematical model of pulsed diffraction in both time and frequency domains and interpret its anomalies. The customary continuous-wave (cw) approximation is corrected for the regime below 3 fs in pulse width, the present state of the art. The time-differentiated aspect of diffraction is linked with old theory and the conservation of energy. Convolution of the pulse with differentiated aperture edges produces traveling waves in the focal plane. Their collision near the focal point corresponds to the cw case. (This is generalized for a Gaussian beam.) Spectral sampling depicts a mode-locked laser of extremely broad spectrum, validating the nonintuitive phenomena. The square-modulus tool is validated for these pulses. Ultrashort pulses are related to data transmission rates above 100 THz. Diffraction anomalies cause confusion and loss of information in the sidelobes. Anomalous diffraction may provide new diagnostics. Diffracted energy (salient sidelobes versus continuum) can measure transform-limited pulse width.
Lasers as Tools for Manufacturing of Durable Goods and Microelectronics | 1996
Tariq Manzur; Anthony J. Demaria; Weiquin Chen; Chandrasekhar Roychoudhuri
We present examples of manufacturing applications like solid freeform fabrication by sintering metal/ceramic powders, and drilling using semiconductor laser diodes. From the stand point of energy requirements, these demonstration indicates that many other laser manufacturing functions like cutting, soldering, marking, printing, etc. can be carried out by currently available commercial laser diodes. Most of these applications are currently being done by the inefficient and bulky lasers like CO2, Nd:YAG and Excimer. These are 30 years matured technologies and still costs over
American Journal of Physics | 1975
Chandrasekhar Roychoudhuri
DOL150/Watt. We believe the price of semiconductor laser diode chips, like computer chips, will come down rapidly, as volume market opens up, from
Proceedings of SPIE | 2011
Chandrasekhar Roychoudhuri
DOL300/Watts today to less than