Multiple tunable laser lines were obtained by pumping solution of Rh6G in ethanol (1mM) by five pairs of the
second harmonic of a passively Q. switched and mode locked Nd:YAG laser. The time delays among the excitation
pulses were varied within coherence length of 1cm. Twenty one equally spaced lines were obtained by pumping dye
solution with ten pairs of excitation beams derived from the same source. It was possible to tune the wavelengths by
a microcontroller based mirror mounted stage. Number of lasing lines varied from minimum five to maximum
twenty one. The wavelength of output lines varied from 540 to 590nm. The pulse lengths were measured, using
Hadland Streak Camera, to vary from minimum 10 to maximum 30ps. The experimental results have lead to
maturity of a 21-lines model of a distributed feedback dye laser. The dye cell was excited by the 2nd harmonic of a
laboratory built passively Q. switched and mode-locked Nd:YAG laser to induce simultaneous temperature phase
grating in the dye solution. This work on distributed feedback dye laser is in agreement with most of the published
results on semiconductor DFB lasers. Simultaneous operation of 21-lines of slightly varying wavelengths opens a
new era of research in biosensors, multiphoton ignition and measurements. This multi-wavelength operation of
DFDL is based on mutual couplings of five overwritten dynamic gratings.
Benefits of laser ignition over the electrical ignition system for Compressed Natural Gas (CNG) engines have fuelled automobile industry and led to an extensive research on basic characteristics to switch over to the emerging technologies. This study was undertaken to determine the electrical and physical characteristics of the electric spark ignition of single cylinder petrol/CNG engine to determine minimum ignition requirements and timeline of ignition events to use in subsequent laser ignition study. This communication briefly reviews the ongoing research activities and reports the results of this experimental study. The premixed petrol and CNG mixtures were
tested for variation of current and voltage characteristics of the spark with speed of engine. The current magnitude of discharge circuit was found to vary linearly over a wide range of speed but the stroke to stroke fire time was found to vary nonlinearly. The DC voltage profiles were observed to fluctuate randomly during ignition process and staying constant in rest of the combustion cycle. Fire to fire peaks of current amplitudes fluctuated up to 10% of the peak
values at constant speed but increased almost linearly with increase in speed. Technical barriers of laser ignition related to threshold minimum ignition energy, inter-pulse durations and firing sequence are discussed. Present findings provide a basic initiative and background information for designing suitable timeline algorithms for laser ignited leaner direct injected CNG engines.
Economic considerations of laser induced ignition over the normal electrical ignition of direct injected Compressed Natural Gas (CNG) engines has motivated automobile industry to go for extensive research on basic characteristics of leaner unconventional fuel mixtures to evaluate practical possibility of switching over to the
emerging technologies. This paper briefly reviews the ongoing research activities on minimum ignition energy and power requirements of natural gas fuels and reports results of present laser air/CNG mixture absorption coefficient study. This study was arranged to determine the thermo-optical characteristics of high air/fuel ratio mixtures using laser techniques. We measured the absorption coefficient using four lasers of multiple wavelengths over a wide
range of temperatures and pressures. The absorption coefficient of mixture was found to vary significantly over change of mixture temperature and probe laser wavelengths. The absorption coefficients of air/CNG mixtures were measured using 20 watts CW/pulsed CO2 laser at 10.6μm, Pulsed Nd:Yag laser at 1.06μm, 532 nm (2nd harmonic) and 4 mW CW HeNe laser at 645 nm and 580 nm for temperatures varying from 290 to 1000K using optical transmission loss technique.
A distributed feedback dye laser (DFDL) was experimentally studied to determine the utmost lower limit on ultrafast pulse generation. The ultimate aim was to determine its suitability as a cheaper high peak power laser source. The dye cell was excited by the second harmonic of a laboratory built cavity dumped passively q switched and modelocked Nd:YAG Laser to induce temperature phase grating in dye solution. Different features studied include threshold conditions, pulse shortening, by reducing cavity length, polymerization limitations, simultaneous induction of multiple superimposed gratings, line narrowing, polarization, temporal and spectral characteristics. The pump polarization affect on dynamic gratings and threshold conditions indicated the number of lasing lines (maximum nine) or intensity of a single line depends upon the state of pump polarization (SOP). Various types of tuning methods such as Bragg index, refractive index, half angle and state of pump polarization were tested for improved divergence, bandwidth, line-width and wider spectral ranges. The combined effect of coherence length and SOP of excitation laser on emission of multiple lines was studied without using external gratings. The results of this critical and contemporary work on DFDL is in agreement with most of the published results and opens a new era for their potential suitability in optical communication, sensing and photonic devices.
Industrial applications of highly repetitive laser may cause precise exposure problems. This paper reports findings of an experimental study on integral gain accretion during repetitive excitation of distributed feedback dye lasers. To estimate the effect 10 to 20 pulses of second harmonic of a passively Q-Switched and mode-locked Nd:YAG laser were used to excite a distributed feedback dye laser (DFDL). The signals of DFDL and Nd:YAG laser were recorded by Imacon 675-streak camera with no relative delay. It was found that the peak of DFDL output envelope of pulses was delayed from peak of the excitation Nd:YAG envelope of pulses by more than one inter- pulse period (2L/C) of excitation laser. Various types of cases such as different excitation energies and inter-pulse time periods were studied and an intensity-based model was developed. Time delay between the peaks of pulse envelopes of Nd:YAG and DFDL was found to depend upon the inter-pulse period (2L/C) of the excitation laser. A computer program was used to simulate the experimentally measured delay to estimate thermal decay constants and energy retained by the medium. It was found that for smaller inter-pulse periods the effect of gradual gain build-up becomes very significant to affect some of the sensitive applications in welding and communication. This effect was used to measure thermal diffusion time constant of dye solutions.
Potential energy sources are being investigated for the socioeconomic needs and increased power demand. Systems employing nuclear, thermal, hydro, solar, volcano, MHD, tidal and wind power generation techniques already exist. This work describes our attempt to utilize the off-planet lightning charge to store super electrolytic batteries or super capacitors. The electrostatic charge on clouds can be shifted to earth through a conducive air plasma channel created by appropriate high power Q-switched and mode-locked laser. The pulsed laser may create a conducting path consisting of ionized air particles from earth to some upper atmosphere. An antenna connected to anode of super cell or positive terminal of the super capacitor will accumulate and store this charge for future use. The anode of battery or positive terminal of capacitor may be connected to earth to complete the circuit. Due to extremely loud thundering and tropical weather severity a detailed work was done on lightning regarding its temporal and spatial profiles to develop a reasonable model to explore transient charging characteristics. Experimental work in respect of laser inducted plasma wire creation and charging capabilities of super storage batteries or super capacitors is optimized. Latest experimental results are reported.
A novel optical displacement sensor based on Bragg effect is described. A green light bema was used to excite a Rh6G dye solution in Shank type geometry. The beam was split up by a dielectric mirror and the two equal intensity vertically polarized light beams were folded by two mirrors to interfere in the dye cell. The lasing wavelength was found to be a precise function of the half angle between the beams. The vibrating body was attached to one of the folding mirror. In normal operation the lasing line wavelength was unchanged but during mirror vibration corresponding to this 1 degree was 87 micrometers . The sensor resolution was about 1.3 angstrom/micrometers . This ultrashell displacement sensor can be used to determine the frequency of vibration or simple displacements in ultraprecise applications.
A passive hologram guided target designation is more superior than simple matrix or image guided system due to its 3D target acquisition and recognition. To implement this criterion a target hologram was loaded into onboard optics that was a part of a dynamic scanning system. The observed data was compared with onboard target hologram and found that the system accuracy was better than the conventional systems. To make the carrier invisible multi-layer coating were used that resulted in perfect concealing of the carrier. Once the target acquisition is compete the locking system stops further comparison and reorients the carrier direction on to the target. This paper critically overviews general principles involved and experimental furtherance in the field of optically guided target designators. There is say that a perfect control of the electromagnetic spectrum can close the eyes or ears and renders the defence blind and deaf. Normally laser and fiber optic guided missiles ar more popular than the conventional guided missiles but our proposed hologram guidance approach is likely to establish its own technical distinct and novelty.
Dye cell in Shank Type Geometry was excited by multiple sets of 2nd harmonic of a laboratory built cavity dumped Nd:YAG laser to induce multiple dynamic gratings at the same spatial location in dye cell. The result of their concurrent operation are presented in this paper. It will be shown that when the delay between the three sets of excitation beams is varied within coherence length of the pump laser, the number of dynamic volume gratings and hence and colors of multiple oscillating lines become tunable. Five lines were observed from two pairs of excitation beams and maximum nine lines for three pairs of beams. The colors of these 9 spectral lines varied from green to pink and were equally spaced in their spectrum. This experimental study was conduced precisely as a function of optical path differences between three sets of excitation beams varying from 1 to 9 mm among three sets of pump beams. The effect of coherence length and state of polarization of excitation laser on emission of multiple lines were investigated. No external gratings were used to excite the gain medium. The objective of this experimental study was to produce multiple laser sources of different colors to interface it to optical integrated circuits for use in image processing, optical interconnections and photonic switching.
Solution of R6G was excited by three pairs of 2nd harmonic of Nd:YAG laser in Shank type geometry to produce multiple dynamic gratings at the same spatial location in dye cell. The result of their concurrent operation are presented in this paper. It will be shown that when the delay between the three sets of excitation beams is varied within coherence length of the pump laser, the number of dynamic volume gratings and hence the colors of multiple oscillating lines become tunable. Five lines were observed for two pairs of excitation beams and maximum nine lines for three pairs of beams. The colors of these 9 spectral lines varied from green to pink and were equally spaced in their spectrum. This experimental study was conducted precisely as a function of optical path differences between three sets of excitation beams varying from 1 to 9 mm among three sets of pump beams. The effect of coherence length and state of polarization of excitation laser on emission of multiple lines were investigated. No external gratings were used to excite the gain medium. The results shown promising applications in photonic switching, optical computing and LANs.
A theoretical model was developed and simulated to confirm the result of our experimental study showing gain accumulation and peak pulse shifting phenomenon during repetitive excitation of distributed feedback dye laser. The dye cell was excited by 10 to 20 pulses of a frequency doubled, passively Q-switched and Mode-locked Nd:YAG laser. The output pulses of DFDL and Nd:YAG laser were investigated by Imacon 675-streak camera. At zero mutual delay of DFDL and Nd:YAG the peak of DFDL output envelope of pulses was delayed from the peak of the excitation Nd:YAG envelope of pulses by more than one inter-pulse period of excitation laser. Various types of cases such as different excitation energies and inter-pulse time periods were studied and a DFDL intensity based model was developed. The delay between the peaks of pulse envelopes of Nd:YAG and DFDL depends upon the inter-pulse period of the excitation laser. A computer program was used to simulate the experimentally measured delay to estimate thermal decay constants and energy retained by the medium. It was found that for smaller inter- pulse periods the effect of gradual gain build-up becomes very significant to effect some of the more sensitive applications such as energy per pulse in laser eye treatment, photonic switching and bit error rate in fiber optic communication.
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