The paper presents the design and performance of a transversely pumped, narrow bandwidth, high wa... more The paper presents the design and performance of a transversely pumped, narrow bandwidth, high wavelength stability tunable dye laser that neither uses low expansion coefficient materials for construction nor incorporates any active control on the wavelength or the dye solution and environmental temperature as generally used in such lasers. The scheme essentially involves designing the mechanical assembly in such a way that, when bolted together it forms a massive monoblock, enclosing all the optical components and the dye laser axis within itself. This ensures the environmental temperature changes can only affect the output characteristics over long time scale. Short term (pulse to pulse) fluctuations in wavelengths and bandwidths, generally associated with the dye flow instabilities, were minimized by using a specially designed a dye cell made of a near 360°-curved rectangular duct, in which the turbulent flow is transformed itself into laminar flow as it reaches the dye laser axi...
Journal of Electron Spectroscopy and Related Phenomena
Abstract The results of investigations conducted on the valence band structure of the near-surfac... more Abstract The results of investigations conducted on the valence band structure of the near-surface atoms of niobium (Nb) sample, taken from a sheet that is used for fabricating superconducting radio frequency (SRF) cavity, are presented. The valence band electronic states were excited using low energy ( ≤ 50 eV) ultraviolet radiation. It was observed that a) the valence band spectrum primarily consists of oxygen 2p-derived states, b) a typical feature expected near the Fermi edge in the valence band of Nb is conspicuously absent. Analysis of the wide band profile provides a number of electronic states peaked at ∼6.3, 7.6, 9.2, and 10.9 eV. After sputtering the surface, a small peak appeared at ∼1.4 eV near the Fermi energy edge. The Nb 4d states showed a resonance involving intra-atomic transition and also hybridization with the states of O 2p. The present study will be useful in identification of the electronic states of Nb that are accountable for superconductivity related issues in an SRF cavity.
Abstract In this paper, we report optical (reflectance) measurements and investigations of optica... more Abstract In this paper, we report optical (reflectance) measurements and investigations of optical properties of electropolished (EP), buffered chemical polished (BCP), and as-received (AR) from vendor niobium (Nb) samples typically used for fabrication of superconducting radio frequency (SCRF) cavities. Optical conductivity ( σ (0), approximated near zero frequency) of EP ( σ (0) ∼ 9 × 10 3 Ω −1 cm −1 ) sample is one order of magnitude higher than that of BCP ( σ (0) ∼ 7 × 10 2 Ω −1 cm −1 ) and AR ( σ (0) ∼ 3 × 10 2 Ω −1 cm −1 ) niobium samples. Furthermore, physical constants of electropolished Nb-SCRF materials such as concentration of conduction electrons ( ∼ 1.8 × 10 22 electrons/cm 3 ), average velocity ( ∼ 5.9 × 10 7 cm/s) of the electrons on the Fermi surface, and mean free path ( ∼ 0.53 nm) were also found to be considerably higher than that of the BCP and the AR samples. The depth of electric field penetration (in low frequency region) in the electropolished Nb sample ( ∼ 80 nm) is appreciably lesser than the BCP ( ∼ 450 nm) and the AR ( ∼ 400 nm) samples.
We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (r... more We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ∼300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm−1), hydrides (1277 and 1385 cm−1: ∼80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm−1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectro...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
Abstract We have investigated the possible influence of surface oxides on the optical properties ... more Abstract We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.
A dye laser pumped by a high repetition rate copper vapor laser (CVL) shows flow-induced variatio... more A dye laser pumped by a high repetition rate copper vapor laser (CVL) shows flow-induced variations in wavelength and bandwidth. A brief description of bandwidth deviations in a flowing rhodamine 6G dye laser, transversely pumped by CVL, is presented. Tunable lasers based on organic dyes have various applications such as resonance ionization mass spectroscopy (RIMS) [1, 2], atomic vapor laser isotope separation (AVLIS) [3-5], ultrafast pulse amplification [6], medical applications [6-8], and more. For these purposes, various types of dye laser sources have been developed and a number of critical parameters affecting their performance have been addressed [7]. Absorption of the pump beams in the dye solution and indirect heating, such as residual absorption in the dye cell windows, cause lack of thermal uniformity [7, 9, 10] in the medium. The amount of heat deposited inside the medium dissipates through conduction and convection, to maintain the thermal equilibrium. Non-uniform heati...
It is proposed that a macroscopic theory of propagation and scattering of light through random me... more It is proposed that a macroscopic theory of propagation and scattering of light through random media can be functional for the dye liquid flowing media in the microscopic levels too, with modest approximations. Maxwell’s equation for a random refractive index medium is approximated and solved for the electric field. An analytical expression for the spectral intensity of the field scattered by the refractive index fluctuations inside a medium has been derived which was valid within the first Born approximation. Far field spectral intensity variation of the radiation propagating through the liquid medium is a consequence of variation in correlation function of the refractive index inhomogeneities. The strength of radiation scattered in a particular direction depends on the spatial correlation function of the refractive index fluctuations of the medium. An attempt is made to explain some of the experimentally observed spectral intensity variations, particularly dye emission propagation...
In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance i... more In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance in a narrow spectral width dispersive resonator, pumped by a high repetition rate copper vapor laser, was investigated. The scheme essentially involves the profiling of the cubical glass and stainless steel cylindrical surface such that convex-plano contour be present near the optical pumping region. The design is an amalgamation of straight and curved periphery to enhance the dye solution flow stabilities near the dye laser axis. A computational fluid dynamics analysis of the liquid flow through this dye cell has been carried out. The dye laser outputs such as optical average power, spectral width and wavelength stability, tuning range, pulse shape, through this new dye cell was evaluated. The dye laser average power about 30 mW was fairly steady over the observation period of more than an hour. The dye laser short-term (1 min) spectral width was within 0.824 ± 0.075 GHz, while, in a long-term, more than an hour, drifted by about 180 MHz. The dye laser wavelength in short-term fluctuates within ±0.0065 nm whereas in a long-term, more than an hour, drifted by about 0.0105 nm. The dye laser tuning range was 10 nm with a sub GHz spectral width operation. The pulse shape of the dye laser follows the pump laser pulse profile. Thus, the dye laser has demonstrated fairly long-term stability, without the use of either low expansion material or close loop control on the output.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) ... more A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) wavelength dependent of Kerr type nonlinear refraction in direct and indirect band gap crystals has been reported in the present work. The Z-scan measurements are recorded for both ZnO and CdI(2) with femtosecond laser pulses while the wavelength dependent of the Kerr nonlinearity are in agreement with a two band model. The wavelength dependence of the 3PA is determined by [(3E(photon)/E(g))-1](5/2)[(3E(photon)/E(g))](-9) in the case of direct band gap crystal and [(3E(photon)±ℏΩ/E(g))-1](5/2)[(3E(photon)±ℏΩ/E(g))](-9) in the case of indirect band gap crystal. In the present investigation the value of 3PA in the case of indirect band gap crystal is lower than the direct band gap crystal which is due to the phonon assisted transition. The materials of large band gap with optical nonlinearity and fast response speed should be dominating factor for further photonic devices such as optical limiters, optical switches and optical modulators. The higher order nonlinear optical effects have also been determined in the present study.
ABSTRACT The free carrier optical nonlinearities in direct and indirect band gap crystals have be... more ABSTRACT The free carrier optical nonlinearities in direct and indirect band gap crystals have been investigated by the use of a single beam Z-scan technique. The values of two-photon absorption coefficient (β), nonlinear index n2(w), the total free carrier absorption cross-section and the change in the refractive index per unit carrier density are determined in both direct and indirect band gap crystals. Smaller values of (β) and in the case of indirect band gap crystals have been attributed to phonon assisted transitions, while the smaller value of n2(w) and is due to the rise in saturation taking place in the absorption.
Science and Technology of Welding and Joining, 2007
Page 1. Published by Maney Publishing (c) IOM Communications Ltd Effect of active flux addition o... more Page 1. Published by Maney Publishing (c) IOM Communications Ltd Effect of active flux addition on laser welding of austenitic stainless steel R. Kaul* 1 , P. Ganesh 1 , N. Singh 2 , R. Jagdheesh 1 , MS Bhagat 1 , H. Kumar 1 , P. Tiwari 3 , HS Vora 2 and AK Nath 1 ...
The paper presents the design and performance of a transversely pumped, narrow bandwidth, high wa... more The paper presents the design and performance of a transversely pumped, narrow bandwidth, high wavelength stability tunable dye laser that neither uses low expansion coefficient materials for construction nor incorporates any active control on the wavelength or the dye solution and environmental temperature as generally used in such lasers. The scheme essentially involves designing the mechanical assembly in such a way that, when bolted together it forms a massive monoblock, enclosing all the optical components and the dye laser axis within itself. This ensures the environmental temperature changes can only affect the output characteristics over long time scale. Short term (pulse to pulse) fluctuations in wavelengths and bandwidths, generally associated with the dye flow instabilities, were minimized by using a specially designed a dye cell made of a near 360°-curved rectangular duct, in which the turbulent flow is transformed itself into laminar flow as it reaches the dye laser axi...
Journal of Electron Spectroscopy and Related Phenomena
Abstract The results of investigations conducted on the valence band structure of the near-surfac... more Abstract The results of investigations conducted on the valence band structure of the near-surface atoms of niobium (Nb) sample, taken from a sheet that is used for fabricating superconducting radio frequency (SRF) cavity, are presented. The valence band electronic states were excited using low energy ( ≤ 50 eV) ultraviolet radiation. It was observed that a) the valence band spectrum primarily consists of oxygen 2p-derived states, b) a typical feature expected near the Fermi edge in the valence band of Nb is conspicuously absent. Analysis of the wide band profile provides a number of electronic states peaked at ∼6.3, 7.6, 9.2, and 10.9 eV. After sputtering the surface, a small peak appeared at ∼1.4 eV near the Fermi energy edge. The Nb 4d states showed a resonance involving intra-atomic transition and also hybridization with the states of O 2p. The present study will be useful in identification of the electronic states of Nb that are accountable for superconductivity related issues in an SRF cavity.
Abstract In this paper, we report optical (reflectance) measurements and investigations of optica... more Abstract In this paper, we report optical (reflectance) measurements and investigations of optical properties of electropolished (EP), buffered chemical polished (BCP), and as-received (AR) from vendor niobium (Nb) samples typically used for fabrication of superconducting radio frequency (SCRF) cavities. Optical conductivity ( σ (0), approximated near zero frequency) of EP ( σ (0) ∼ 9 × 10 3 Ω −1 cm −1 ) sample is one order of magnitude higher than that of BCP ( σ (0) ∼ 7 × 10 2 Ω −1 cm −1 ) and AR ( σ (0) ∼ 3 × 10 2 Ω −1 cm −1 ) niobium samples. Furthermore, physical constants of electropolished Nb-SCRF materials such as concentration of conduction electrons ( ∼ 1.8 × 10 22 electrons/cm 3 ), average velocity ( ∼ 5.9 × 10 7 cm/s) of the electrons on the Fermi surface, and mean free path ( ∼ 0.53 nm) were also found to be considerably higher than that of the BCP and the AR samples. The depth of electric field penetration (in low frequency region) in the electropolished Nb sample ( ∼ 80 nm) is appreciably lesser than the BCP ( ∼ 450 nm) and the AR ( ∼ 400 nm) samples.
We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (r... more We present investigations of the presence of oxides, hydrides, and hydrocarbons in high-purity (residual resistivity ratio, ∼300) niobium (Nb) materials used in fabrication of superconducting radio frequency (SRF) cavities for particle accelerators. Raman spectroscopy of Nb materials (as-received from the vendor as well as after surface chemical- and thermal processing) revealed numerous peaks, which evidently show the presence of oxides (550 cm−1), hydrides (1277 and 1385 cm−1: ∼80 K temperature), and groups of hydrocarbons (1096, 2330, 2710, 2830, 2868, and 3080 cm−1). The present work provides direct spectroscopic evidence of hydrides in the electropolished Nb materials typically used in SRF cavities. Raman spectroscopy thus can provide vital information about the near-surface chemical species in niobium materials and will help in identifying the cause for the performance degradation of SRF cavities. Furthermore, photoelectron spectroscopy was performed on the Nb samples to complement the Raman spectro...
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2016
Abstract We have investigated the possible influence of surface oxides on the optical properties ... more Abstract We have investigated the possible influence of surface oxides on the optical properties of a high-purity niobium (Nb) material for fabrication of superconducting radio frequency (SCRF) cavities. Various peaks in the infrared region were identified using Fourier transform infrared and Raman spectroscopy. Optical response functions such as complex refractive index, dielectric and conductivity of niobium were compared with the existing results on oxides free Nb and Cu. It was observed that the presence of a mixture of niobium-oxides, and probably near other surface impurities, appreciably influence the conducting properties of the material causing deviation from the typical metallic characteristics. In this way, the key result of this work is the observation, identification of vibrational modes of some of surface complexes and study of its influences on the optical responses of materials. This method of spectroscopic investigation will help in understanding the origin of degradation of performance of SCRF cavities.
A dye laser pumped by a high repetition rate copper vapor laser (CVL) shows flow-induced variatio... more A dye laser pumped by a high repetition rate copper vapor laser (CVL) shows flow-induced variations in wavelength and bandwidth. A brief description of bandwidth deviations in a flowing rhodamine 6G dye laser, transversely pumped by CVL, is presented. Tunable lasers based on organic dyes have various applications such as resonance ionization mass spectroscopy (RIMS) [1, 2], atomic vapor laser isotope separation (AVLIS) [3-5], ultrafast pulse amplification [6], medical applications [6-8], and more. For these purposes, various types of dye laser sources have been developed and a number of critical parameters affecting their performance have been addressed [7]. Absorption of the pump beams in the dye solution and indirect heating, such as residual absorption in the dye cell windows, cause lack of thermal uniformity [7, 9, 10] in the medium. The amount of heat deposited inside the medium dissipates through conduction and convection, to maintain the thermal equilibrium. Non-uniform heati...
It is proposed that a macroscopic theory of propagation and scattering of light through random me... more It is proposed that a macroscopic theory of propagation and scattering of light through random media can be functional for the dye liquid flowing media in the microscopic levels too, with modest approximations. Maxwell’s equation for a random refractive index medium is approximated and solved for the electric field. An analytical expression for the spectral intensity of the field scattered by the refractive index fluctuations inside a medium has been derived which was valid within the first Born approximation. Far field spectral intensity variation of the radiation propagating through the liquid medium is a consequence of variation in correlation function of the refractive index inhomogeneities. The strength of radiation scattered in a particular direction depends on the spatial correlation function of the refractive index fluctuations of the medium. An attempt is made to explain some of the experimentally observed spectral intensity variations, particularly dye emission propagation...
In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance i... more In this paper, a new dye cell for transverse pumping was designed, modeled, and its performance in a narrow spectral width dispersive resonator, pumped by a high repetition rate copper vapor laser, was investigated. The scheme essentially involves the profiling of the cubical glass and stainless steel cylindrical surface such that convex-plano contour be present near the optical pumping region. The design is an amalgamation of straight and curved periphery to enhance the dye solution flow stabilities near the dye laser axis. A computational fluid dynamics analysis of the liquid flow through this dye cell has been carried out. The dye laser outputs such as optical average power, spectral width and wavelength stability, tuning range, pulse shape, through this new dye cell was evaluated. The dye laser average power about 30 mW was fairly steady over the observation period of more than an hour. The dye laser short-term (1 min) spectral width was within 0.824 ± 0.075 GHz, while, in a long-term, more than an hour, drifted by about 180 MHz. The dye laser wavelength in short-term fluctuates within ±0.0065 nm whereas in a long-term, more than an hour, drifted by about 0.0105 nm. The dye laser tuning range was 10 nm with a sub GHz spectral width operation. The pulse shape of the dye laser follows the pump laser pulse profile. Thus, the dye laser has demonstrated fairly long-term stability, without the use of either low expansion material or close loop control on the output.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2012
A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) ... more A systematic investigation on nonlinear optical properties such as three photon absorption (3PA) wavelength dependent of Kerr type nonlinear refraction in direct and indirect band gap crystals has been reported in the present work. The Z-scan measurements are recorded for both ZnO and CdI(2) with femtosecond laser pulses while the wavelength dependent of the Kerr nonlinearity are in agreement with a two band model. The wavelength dependence of the 3PA is determined by [(3E(photon)/E(g))-1](5/2)[(3E(photon)/E(g))](-9) in the case of direct band gap crystal and [(3E(photon)±ℏΩ/E(g))-1](5/2)[(3E(photon)±ℏΩ/E(g))](-9) in the case of indirect band gap crystal. In the present investigation the value of 3PA in the case of indirect band gap crystal is lower than the direct band gap crystal which is due to the phonon assisted transition. The materials of large band gap with optical nonlinearity and fast response speed should be dominating factor for further photonic devices such as optical limiters, optical switches and optical modulators. The higher order nonlinear optical effects have also been determined in the present study.
ABSTRACT The free carrier optical nonlinearities in direct and indirect band gap crystals have be... more ABSTRACT The free carrier optical nonlinearities in direct and indirect band gap crystals have been investigated by the use of a single beam Z-scan technique. The values of two-photon absorption coefficient (β), nonlinear index n2(w), the total free carrier absorption cross-section and the change in the refractive index per unit carrier density are determined in both direct and indirect band gap crystals. Smaller values of (β) and in the case of indirect band gap crystals have been attributed to phonon assisted transitions, while the smaller value of n2(w) and is due to the rise in saturation taking place in the absorption.
Science and Technology of Welding and Joining, 2007
Page 1. Published by Maney Publishing (c) IOM Communications Ltd Effect of active flux addition o... more Page 1. Published by Maney Publishing (c) IOM Communications Ltd Effect of active flux addition on laser welding of austenitic stainless steel R. Kaul* 1 , P. Ganesh 1 , N. Singh 2 , R. Jagdheesh 1 , MS Bhagat 1 , H. Kumar 1 , P. Tiwari 3 , HS Vora 2 and AK Nath 1 ...
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