C. Rablau - Academia.edu (original) (raw)

Papers by C. Rablau

We report on the investigation of several fiber-optic devices as potential sensors for temperatur... more We report on the investigation of several fiber-optic devices as potential sensors for temperature measurements in AC magnetic fields. Common temperature sensors, such as thermocouples, thermistors or diodes, will create random and/or systematic errors when placed in a magnetic field. A DC magnetic field is susceptible to create a systematic offset to the measurement, while in an AC magnetic field of variable frequency random errors which cannot be corrected for can also be introduced. Fiber-Bragg-gratings and thin film filters have an inherent temperature dependence. Detrimental for their primary applications, the same dependence allows one to use such devices as temperature sensors. In an AC magnetic field, they present the advantage of being immune to electromagnetic interference. Moreover, for fiber-Bragg-gratings, the shape factor and small mass of the bare-fiber device make it convenient for temperature measurements on small samples. We studied several thin-film filters and fi...

Journal of Applied Physics, 2015

We report a novel method of determining the average Néel relaxation time and its temperature depe... more We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe 3 O 4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H 0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m 3 , in agreement with previously published results.

MRS Proceedings, 1997

Cadmium zinc telluride (CdZnTe) is an emerging material for room-temperature x-ray and gamma ray ... more Cadmium zinc telluride (CdZnTe) is an emerging material for room-temperature x-ray and gamma ray detectors. The identification and control of point defects and charge compensators are currently important issues. Low-temperature photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies have been used to characterize point defects in CdZnTe crystals grown by the high-pressure Bridgman technique. Luminescence due to shallow donors, shallow acceptors, and deeper acceptors was monitored for a series of samples. An isotropic EPR signal attributed to shallow hydrogenic donors is observed in all samples, and the concentration of shallow donors has been determined. The nature of the defect centers (impurities, vacancies, vacancy-impurity complexes), and the correlation between defect concentration and device performance is discussed.

Computer aided surgery : official journal of the International Society for Computer Aided Surgery, 2013

This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be use... more This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system w...

Journal of Magnetism and Magnetic Materials, 2008

CoxFe3− xO4 (0⩽ x⩽ 0.10) nanoparticles coated with tetramethyl ammonium hydroxide as a surfactant... more CoxFe3− xO4 (0⩽ x⩽ 0.10) nanoparticles coated with tetramethyl ammonium hydroxide as a surfactant were synthesized by a co-precipitation technique. The Fe: Co ratio was tuned up to x= 0.10 by controlling the Co2+ concentration during synthesis. The mean particle size, ...

Journal of Electronic Materials, 2002

Journal of Electronic Materials, 1998

Cd1−xZnxTe (CZT) is an emerging material for room-temperature x-ray and gamma-ray detectors. The ... more Cd1−xZnxTe (CZT) is an emerging material for room-temperature x-ray and gamma-ray detectors. The identification and control of point defects and charge compensators in the bulk material are currently important issues. We have used photoluminescence (PL), photoluminescence excitation, and electron paramagnetic resonance (EPR) to characterize point defects in a series of bulk CZT crystals grown by the high-pressure Bridgman technique. Luminescence

Journal of Crystal Growth, 2001

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions f... more We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8μs were measured for samples with Cr2+ concentrations from low 1017 to high 1018cm− 3 range. Lifetime data taken ...

Journal of Applied Physics, 2001

Photoluminescence and optical absorption spectroscopies have been used to study bulk ZnGeP2. Two ... more Photoluminescence and optical absorption spectroscopies have been used to study bulk ZnGeP2. Two sharp zero-phonon lines with opposite polarizations are resolved in emission at 1.7849 eV (at 70 K) and 1.7784 eV (at 5 K), respectively. Thermalization occurs between these two lines, suggesting a split excited state of the center. Considerable structural detail is resolved in the vibronic sidebands of these lines, revealing phonon energies of 6.3±0.1 meV and 43.7±0.1 meV. Similar phonon energies are resolved in low-temperature absorption spectra. These results for ZnGeP2 are explained by a model of radiative recombination of excitons bound to an isoelectronic defect center. The observed polarization behavior of the sharp-line spectra can be produced by the built-in tetragonal distortion along the c axis associated with the chalcopyrite structure.

Applied Optics, 2006

ABSTRACT We present a study of the sidewall surface quality inside microchannels fabricated in fu... more ABSTRACT We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.

to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanop... more to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for γ-Fe 2 O 3 alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results 1 where both samples exhibited Neel relaxation but only the Fe 3 O 4 ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems.

We report studies of the structural, magnetic, magneto-thermal and magneto-optic properties of de... more We report studies of the structural, magnetic, magneto-thermal and magneto-optic properties of dextran, oleic acid, lauric acid and myristic acid surfacted Fe 3 O 4 nanoparticles of hydrodynamic sizes ranging from 32 nm to 92 nm. All the samples showed saturation magnetization of ∼50 emu/g, significantly smaller than the bulk value for Fe 3 O 4 , together with superparamagnetic behavior. The ac magnetization measurements on the dextran coated nanoparticles showed frequency dependent blocking temperature, consistent with superparamgnetic blocking. The ferrofluid heating rates in a 250 Gauss, 100 kHz ac magnetic field varied with the chain lengths of the surfactants, with higher heating rates for longer chains. DC-magnetic-field-induced light scattering patterns produced by two orthogonal He-Ne laser beams passing through the ferrofluid sample revealed different optical signatures for different surfactants.

Journal of Electronic Materials, 1999

ZnSe:Cr 2+ is an attractive candidate as a room-temperature tunable solid-state laser with output... more ZnSe:Cr 2+ is an attractive candidate as a room-temperature tunable solid-state laser with output in the 2-3 µm range. Passive absorption losses in this emission range currently limit laser performance. In this study, we use absorption and photoluminescence spectroscopies at 5 and 296K to address the origin of these optical losses. A series of diffusion-doped ZnSe:Cr single-crystal samples with Cr 2+ concentrations in the range from 2 × 10 17 cm-3 to 9 × 10 19 cm-3 were obtained using CrSe powder as the dopant source. We find that trace amounts of Fe 2+ produce absorption in the 2-3 µm range. Also, we have obtained data on a 680 nm absorption band observed in ZnSe:Cr which has been assigned to an internal transition of Cr 2+. In our series of samples, the relative intensities of the 680 nm absorption band do not track the relative intensities of the 1.8 µm band (known to be due to Cr 2+), although excitation near 680 nm does produce weak Cr 2+ luminescence. Our absorption data do not support the current assignment of the 680 nm absorption as being an internal transition of the Cr 2+ ion.

Journal of Crystal Growth, 2000

ABSTRACT Solid-state tunable laser sources in the mid-IR region have been recently investigated f... more ABSTRACT Solid-state tunable laser sources in the mid-IR region have been recently investigated for their potential in remote sensing applications. Room temperature lasers based on single crystals of chromium-doped CdSe are particularly interesting due to their broad band tunability beyond 2μm spectral region. In this study, we have grown doped single crystals by the high-temperature gradient freezing solution technique, using selenium as the solvent. Crystals of 1.2cm in diameter and up to 7cm long, cracks and precipitates free could be obtained. The effective segregation coefficient of Cr2+ ions along the ingot was evaluated. Room temperature emission lifetime values of 3.0–4.5μs were measured.

We have investigated the aggregation and dissociation dynamics of 6-nm size Fe 3 O 4 nanoparticle... more We have investigated the aggregation and dissociation dynamics of 6-nm size Fe 3 O 4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size γ-Fe 2 O 3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns. For the Fe 3 O 4 ferrofluid, a strong anisotropy in light scattering was observed for light propagating perpendicular to the magnetic field. This behavior is attributed to the aggregation of the nanoparticles into chain-like and column-like structures oriented parallel to the magnetic field. A significantly different behavior is observed for the aqueous suspension of γ-Fe 2 O 3 nanoparticles precipitated in alginate hydrogel, for which the application of the dc magnetic field produced little to no change in the light scattering patterns. We attribute this difference to the constrained random distribution of γ-Fe 2 O 3 nanoparticles precipitated in the alginate matrix. Correlating the results from this investigation with our previous study of magneto-thermal measurements in ac fields [Vaishnava et al., J. Appl. Phys. 102, 063914 (2007)], we conclude that for a ferrofluid to exhibit significant thermal effects under an ac magnetic field, it should exhibit optical anisotropy by developing a chain like structure under the influence of a dc magnetic field.

We report an experimental investigation of time dependent anisotropic light scattering by an aque... more We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe 3 O 4 nanoparticles ͑ϳ6 nm͒ under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.

Journal of Crystal Growth, 2001

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions f... more We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8μs were measured for samples with Cr2+ concentrations from low 1017 to high 1018cm− 3 range. Lifetime data taken ...

We report on the investigation of several fiber-optic devices as potential sensors for temperatur... more We report on the investigation of several fiber-optic devices as potential sensors for temperature measurements in AC magnetic fields. Common temperature sensors, such as thermocouples, thermistors or diodes, will create random and/or systematic errors when placed in a magnetic field. A DC magnetic field is susceptible to create a systematic offset to the measurement, while in an AC magnetic field of variable frequency random errors which cannot be corrected for can also be introduced. Fiber-Bragg-gratings and thin film filters have an inherent temperature dependence. Detrimental for their primary applications, the same dependence allows one to use such devices as temperature sensors. In an AC magnetic field, they present the advantage of being immune to electromagnetic interference. Moreover, for fiber-Bragg-gratings, the shape factor and small mass of the bare-fiber device make it convenient for temperature measurements on small samples. We studied several thin-film filters and fi...

Journal of Applied Physics, 2015

We report a novel method of determining the average Néel relaxation time and its temperature depe... more We report a novel method of determining the average Néel relaxation time and its temperature dependence by calculating derivatives of the measured time dependence of temperature for a frozen ferrofluid exposed to an alternating magnetic field. The ferrofluid, composed of dextran-coated Fe 3 O 4 nanoparticles (diameter 13.7 nm ± 4.7 nm), was synthesized via wet chemical precipitation and characterized by x-ray diffraction and transmission electron microscopy. An alternating magnetic field of constant amplitude (H 0 = 20 kA/m) driven at frequencies of 171 kHz, 232 kHz and 343 kHz was used to determine the temperature dependent magnetic energy absorption rate in the temperature range from 160 K to 210 K. We found that the specific absorption rate of the ferrofluid decreased monotonically with temperature over this range at the given frequencies. From these measured data, we determined the temperature dependence of the Néel relaxation time and estimate a room-temperature magnetocrystalline anisotropy constant of 40 kJ/m 3 , in agreement with previously published results.

MRS Proceedings, 1997

Cadmium zinc telluride (CdZnTe) is an emerging material for room-temperature x-ray and gamma ray ... more Cadmium zinc telluride (CdZnTe) is an emerging material for room-temperature x-ray and gamma ray detectors. The identification and control of point defects and charge compensators are currently important issues. Low-temperature photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies have been used to characterize point defects in CdZnTe crystals grown by the high-pressure Bridgman technique. Luminescence due to shallow donors, shallow acceptors, and deeper acceptors was monitored for a series of samples. An isotropic EPR signal attributed to shallow hydrogenic donors is observed in all samples, and the concentration of shallow donors has been determined. The nature of the defect centers (impurities, vacancies, vacancy-impurity complexes), and the correlation between defect concentration and device performance is discussed.

Computer aided surgery : official journal of the International Society for Computer Aided Surgery, 2013

This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be use... more This paper presents an enhanced haptic-enabled master-slave teleoperation system which can be used to provide force feedback to surgeons in minimally invasive surgery (MIS). One of the research goals was to develop a combined-control architecture framework that included both direct force reflection (DFR) and position-error-based (PEB) control strategies. To achieve this goal, it was essential to measure accurately the direct contact forces between deformable bodies and a robotic tool tip. To measure the forces at a surgical tool tip and enhance the performance of the teleoperation system, an optical force sensor was designed, prototyped, and added to a robot manipulator. The enhanced teleoperation architecture was formulated by developing mathematical models for the optical force sensor, the extended slave robot manipulator, and the combined-control strategy. Human factor studies were also conducted to (a) examine experimentally the performance of the enhanced teleoperation system w...

Journal of Magnetism and Magnetic Materials, 2008

CoxFe3− xO4 (0⩽ x⩽ 0.10) nanoparticles coated with tetramethyl ammonium hydroxide as a surfactant... more CoxFe3− xO4 (0⩽ x⩽ 0.10) nanoparticles coated with tetramethyl ammonium hydroxide as a surfactant were synthesized by a co-precipitation technique. The Fe: Co ratio was tuned up to x= 0.10 by controlling the Co2+ concentration during synthesis. The mean particle size, ...

Journal of Electronic Materials, 2002

Journal of Electronic Materials, 1998

Cd1−xZnxTe (CZT) is an emerging material for room-temperature x-ray and gamma-ray detectors. The ... more Cd1−xZnxTe (CZT) is an emerging material for room-temperature x-ray and gamma-ray detectors. The identification and control of point defects and charge compensators in the bulk material are currently important issues. We have used photoluminescence (PL), photoluminescence excitation, and electron paramagnetic resonance (EPR) to characterize point defects in a series of bulk CZT crystals grown by the high-pressure Bridgman technique. Luminescence

Journal of Crystal Growth, 2001

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions f... more We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8μs were measured for samples with Cr2+ concentrations from low 1017 to high 1018cm− 3 range. Lifetime data taken ...

Journal of Applied Physics, 2001

Photoluminescence and optical absorption spectroscopies have been used to study bulk ZnGeP2. Two ... more Photoluminescence and optical absorption spectroscopies have been used to study bulk ZnGeP2. Two sharp zero-phonon lines with opposite polarizations are resolved in emission at 1.7849 eV (at 70 K) and 1.7784 eV (at 5 K), respectively. Thermalization occurs between these two lines, suggesting a split excited state of the center. Considerable structural detail is resolved in the vibronic sidebands of these lines, revealing phonon energies of 6.3±0.1 meV and 43.7±0.1 meV. Similar phonon energies are resolved in low-temperature absorption spectra. These results for ZnGeP2 are explained by a model of radiative recombination of excitons bound to an isoelectronic defect center. The observed polarization behavior of the sharp-line spectra can be produced by the built-in tetragonal distortion along the c axis associated with the chalcopyrite structure.

Applied Optics, 2006

ABSTRACT We present a study of the sidewall surface quality inside microchannels fabricated in fu... more ABSTRACT We present a study of the sidewall surface quality inside microchannels fabricated in fused silica glass by femtosecond laser pulses and chemical etching. Multiple combinations of laser exposure and etching solution parameters were examined. Results of scanning electron microscopy, atomic force microscopy, and optical reflection analyses of the surfaces are presented. The results obtained demonstrate the feasibility of optical quality surface fabrication, which in turn demonstrates the feasibility of fabricating complex integrated devices containing microfluidic channels and optical waveguides in the glass substrates.

to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanop... more to the magnetic fields. This behavior is attributed to the alignment and aggregation of the nanoparticles in chain-like structures. A very different light scattering behavior was observed for γ-Fe 2 O 3 alginate sample where, under the similar conditions, the application of the magnetic field produced no structured change in scattering. We attribute this difference to the absence of chain-like structures and constrained mobility of iron nanoparticles in the alginate sample. The observation is in agreement with our relaxation and dissipative heating results 1 where both samples exhibited Neel relaxation but only the Fe 3 O 4 ferrofluid showed Brownian relaxation. The results suggest that Brownian relaxation and nanoparticle mobility are important for producing non-linear light scattering in such systems.

We report studies of the structural, magnetic, magneto-thermal and magneto-optic properties of de... more We report studies of the structural, magnetic, magneto-thermal and magneto-optic properties of dextran, oleic acid, lauric acid and myristic acid surfacted Fe 3 O 4 nanoparticles of hydrodynamic sizes ranging from 32 nm to 92 nm. All the samples showed saturation magnetization of ∼50 emu/g, significantly smaller than the bulk value for Fe 3 O 4 , together with superparamagnetic behavior. The ac magnetization measurements on the dextran coated nanoparticles showed frequency dependent blocking temperature, consistent with superparamgnetic blocking. The ferrofluid heating rates in a 250 Gauss, 100 kHz ac magnetic field varied with the chain lengths of the surfactants, with higher heating rates for longer chains. DC-magnetic-field-induced light scattering patterns produced by two orthogonal He-Ne laser beams passing through the ferrofluid sample revealed different optical signatures for different surfactants.

Journal of Electronic Materials, 1999

ZnSe:Cr 2+ is an attractive candidate as a room-temperature tunable solid-state laser with output... more ZnSe:Cr 2+ is an attractive candidate as a room-temperature tunable solid-state laser with output in the 2-3 µm range. Passive absorption losses in this emission range currently limit laser performance. In this study, we use absorption and photoluminescence spectroscopies at 5 and 296K to address the origin of these optical losses. A series of diffusion-doped ZnSe:Cr single-crystal samples with Cr 2+ concentrations in the range from 2 × 10 17 cm-3 to 9 × 10 19 cm-3 were obtained using CrSe powder as the dopant source. We find that trace amounts of Fe 2+ produce absorption in the 2-3 µm range. Also, we have obtained data on a 680 nm absorption band observed in ZnSe:Cr which has been assigned to an internal transition of Cr 2+. In our series of samples, the relative intensities of the 680 nm absorption band do not track the relative intensities of the 1.8 µm band (known to be due to Cr 2+), although excitation near 680 nm does produce weak Cr 2+ luminescence. Our absorption data do not support the current assignment of the 680 nm absorption as being an internal transition of the Cr 2+ ion.

Journal of Crystal Growth, 2000

ABSTRACT Solid-state tunable laser sources in the mid-IR region have been recently investigated f... more ABSTRACT Solid-state tunable laser sources in the mid-IR region have been recently investigated for their potential in remote sensing applications. Room temperature lasers based on single crystals of chromium-doped CdSe are particularly interesting due to their broad band tunability beyond 2μm spectral region. In this study, we have grown doped single crystals by the high-temperature gradient freezing solution technique, using selenium as the solvent. Crystals of 1.2cm in diameter and up to 7cm long, cracks and precipitates free could be obtained. The effective segregation coefficient of Cr2+ ions along the ingot was evaluated. Room temperature emission lifetime values of 3.0–4.5μs were measured.

We have investigated the aggregation and dissociation dynamics of 6-nm size Fe 3 O 4 nanoparticle... more We have investigated the aggregation and dissociation dynamics of 6-nm size Fe 3 O 4 nanoparticles coated by tetra methyl ammonium hydroxide (TMAH) and the same size γ-Fe 2 O 3 nanoparticles precipitated inside an alginate hydrogel matrix, both in aqueous suspensions, using dc magnetic-field-induced time-dependent light scattering patterns. For the Fe 3 O 4 ferrofluid, a strong anisotropy in light scattering was observed for light propagating perpendicular to the magnetic field. This behavior is attributed to the aggregation of the nanoparticles into chain-like and column-like structures oriented parallel to the magnetic field. A significantly different behavior is observed for the aqueous suspension of γ-Fe 2 O 3 nanoparticles precipitated in alginate hydrogel, for which the application of the dc magnetic field produced little to no change in the light scattering patterns. We attribute this difference to the constrained random distribution of γ-Fe 2 O 3 nanoparticles precipitated in the alginate matrix. Correlating the results from this investigation with our previous study of magneto-thermal measurements in ac fields [Vaishnava et al., J. Appl. Phys. 102, 063914 (2007)], we conclude that for a ferrofluid to exhibit significant thermal effects under an ac magnetic field, it should exhibit optical anisotropy by developing a chain like structure under the influence of a dc magnetic field.

We report an experimental investigation of time dependent anisotropic light scattering by an aque... more We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe 3 O 4 nanoparticles ͑ϳ6 nm͒ under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.

Journal of Crystal Growth, 2001

We report the investigation by photoluminescence lifetime measurements of the near-IR emissions f... more We report the investigation by photoluminescence lifetime measurements of the near-IR emissions from a series of chromium-doped ZnSe samples, correlated to their preparation conditions. The samples were polycrystalline or single crystals prepared by post growth diffusion doping or single crystals doped during growth by the physical vapor transport method. Room temperature lifetime values between 6 and 8μs were measured for samples with Cr2+ concentrations from low 1017 to high 1018cm− 3 range. Lifetime data taken ...