Polymers and glasses are important materials for non-silicon MEMS devices. Precision structuring ... more Polymers and glasses are important materials for non-silicon MEMS devices. Precision structuring of such materials has been plagued by the lack of proper tools capable of producing the required intricate details and finish quality. Machining with high peak power, short pulse lasers has become a potential technique for such applications due to the reduced thermal damage, high precision, small feature size and flexibility in pattern generation. In particular, the nanosecond and femtosecond pulsed lasers offer significant advantages with the ability to deposit energy in materials in a very short time interval, hence ensuring efficient conversion of the energy for material removal.In this paper, the results of using femtosecond laser to process polycarbonate, aluminosilicate glasses and nanosecond laser processing of aluminosilicate glasses are discussed. High quality microchannels in polycarbonate and glass substrates for a bubble switch have been created. The critical dimensions are a...
We describe a novel set of laser processes for the CIGS P1, P2 and P3 scribing steps, the develop... more We describe a novel set of laser processes for the CIGS P1, P2 and P3 scribing steps, the development of which has been enabled by a unique pulse-programmable fiber laser. We find that the unique pulse control properties of this 1064 nm wavelength laser have significant effects on the material removal dynamics of the various film layers in the CIGS
Spatial beam shaping has long been utilized to improve laser processes and has often generated sp... more Spatial beam shaping has long been utilized to improve laser processes and has often generated spectacular improvements in the end results. Until recently the temporal shape of laser pulses has been limited by the design parameters of the laser cavities and shaping in the temporal domain has remained relatively unexplored. The advent of the MOPA fiber laser has opened the door to creating arbitrary temporal waveforms with shape, energy, and duration being entirely independent from the laser repetition rate and changeable "on the fly." This new degree of freedom in the laser processing parameter space has not only enabled new and improved laser processes but provided a new tool to study the dynamics of the laser material interaction itself which can greatly speed process development. Furthermore having this flexibility allows a single laser to cover a range of process parameters that heretofore normally required using several separate laser system. In this work we report on the application of temporal pulse shaping to CIGS P2 & P3 processing, CIGS P1 processing (molybdenum on glass), a-Silicon P1 processing (ZnO on glass), c-Silicon via hole drilling for emitter wrap through (EWT) and other processes using the PyroFlex 25 pulse programmable fiber laser. The temporal pulse shaping feature of the laser is demonstrated as a tool to probe the process dynamics and speed up the determination of optimal process parameters. When applicable, results between the pulse shape of a traditional laser and an optimized laser pulse shapes are compared.
This paper describes a robust mixed-synthesis controller for shape memory alloy (SMA) actuators. ... more This paper describes a robust mixed-synthesis controller for shape memory alloy (SMA) actuators. The weights for the controller are chosen such that the disturbance rejection criterion is met for low frequencies and robust stability is maintained for high frequencies. Simulation and experimental results show fast and accurate response for strain in the SMA under no perturbation. The performance of the
A computer vision system which performs real-time mode control of a high powered CO* laser has be... more A computer vision system which performs real-time mode control of a high powered CO* laser has been developed. The device continuously monitors the output beam to derive alignment data for the primary resonator optic. The technique ensures that the laser's intensity distribution is as uniform as possible. Valuable profile data and beam diagnostics are also generated by the system.
This paper describes a gain-scheduled controller for a shape memory alloy (SMA) actuator. For acc... more This paper describes a gain-scheduled controller for a shape memory alloy (SMA) actuator. For accurate control of an SMA actuator, it is important to develop a precise model for the SMA. A model has been proposed based on concepts from physics. The equations include Joules heating - convectional cooling to explain the dynamics of temperature, Fermi-Dirac statistics to explain the
ABSTRACT Laser surface texturing process involves creation of microfeatures, e.g., tiny dimples, ... more ABSTRACT Laser surface texturing process involves creation of microfeatures, e.g., tiny dimples, usually distributed in a certain pattern, covering only a fraction of the surface of the material that is being treated. The process offers several advantages for tribological applications, including improved load capacity, wear resistance, lubrication lifetime, and reduced friction coefficient. In the present study, the surface modification of gray cast iron, using millisecond (λ = 1,064 nm), nanosecond (λ = 1,064 nm) and femtosecond (λ = 800 nm) pulse duration laser irradiation, is adopted to establish a particular geometrical pattern with dimple features and dimensions, to improve wear and friction behavior. The effect of various laser processing parameters, including laser pulse energy, pulse duration and processing speed, on the performance characteristics of the laser-treated samples is investigated. The microtextured surfaces were produced on gray cast iron using different millisecond (0.5 ms), nanosecond (40 ns) and femtosecond (120 fs) laser source with the dimple depth between 3 and 15 μm. The coefficient of friction for the untextured surface was ~0.55, millisecond laser textured ~0.31, nanosecond laser textured ~0.02 and femtosecond laser ~0.01, under normal force of 50 N and sliding speed of 63 mm/s. Surface texturing of the gray cast iron surface using femtosecond pulse duration resulted in significant improvement in wear resistance in comparison to the untextured as well as millisecond and nanosecond laser-textured surface.
Ahstract : The usefulness of a particular type of dietary protein for a quicker acclimatization t... more Ahstract : The usefulness of a particular type of dietary protein for a quicker acclimatization to simulated high altitude stress was investigated in albino rats, by studying the changes occurring in the levels of urea cycle enzymes in liver. A good quality protein in (ega) and a ...
Changes in dietary protein quality and high altitude stress alter the serum urea cycle enzyme act... more Changes in dietary protein quality and high altitude stress alter the serum urea cycle enzyme activities. To find a dietary protein which will facilitate quicker acclimatization to altitude stress, groups of rats were fed two diets, isocaloric and isonitrogenous, but differing in amino acid make up. The rats were exposed to simulated altitude stress of 0.5 atmospheric pressure for various periods up to 65 h. When serum arginase and ornithine transcarbamylase activities were assayed, it was seen that the group on the unbalanced protein (Cajanus cajan) diet showed less increase on exposure and a tendency to return to normal level earlier than the group on the balanced protein (egg) diet.
Measurements of the electron density within a photo-initiated, impulse-enhanced, electrically exc... more Measurements of the electron density within a photo-initiated, impulse-enhanced, electrically excited (PIE) laser gas discharge are presented. Ion current measurements were made using a single Langmuir electrostatic probe positioned within the laser discharge volume. Calculations of the electron density were made utilizing a thick-sheath analysis. The results indicate that the electron density increases by two orders of magnitude as the pulser power level is increased. In addition, the electron density was observed to decrease markedly as the dc discharge current was increased.
Polymers and glasses are important materials for non-silicon MEMS devices. Precision structuring ... more Polymers and glasses are important materials for non-silicon MEMS devices. Precision structuring of such materials has been plagued by the lack of proper tools capable of producing the required intricate details and finish quality. Machining with high peak power, short pulse lasers has become a potential technique for such applications due to the reduced thermal damage, high precision, small feature size and flexibility in pattern generation. In particular, the nanosecond and femtosecond pulsed lasers offer significant advantages with the ability to deposit energy in materials in a very short time interval, hence ensuring efficient conversion of the energy for material removal.In this paper, the results of using femtosecond laser to process polycarbonate, aluminosilicate glasses and nanosecond laser processing of aluminosilicate glasses are discussed. High quality microchannels in polycarbonate and glass substrates for a bubble switch have been created. The critical dimensions are a...
We describe a novel set of laser processes for the CIGS P1, P2 and P3 scribing steps, the develop... more We describe a novel set of laser processes for the CIGS P1, P2 and P3 scribing steps, the development of which has been enabled by a unique pulse-programmable fiber laser. We find that the unique pulse control properties of this 1064 nm wavelength laser have significant effects on the material removal dynamics of the various film layers in the CIGS
Spatial beam shaping has long been utilized to improve laser processes and has often generated sp... more Spatial beam shaping has long been utilized to improve laser processes and has often generated spectacular improvements in the end results. Until recently the temporal shape of laser pulses has been limited by the design parameters of the laser cavities and shaping in the temporal domain has remained relatively unexplored. The advent of the MOPA fiber laser has opened the door to creating arbitrary temporal waveforms with shape, energy, and duration being entirely independent from the laser repetition rate and changeable "on the fly." This new degree of freedom in the laser processing parameter space has not only enabled new and improved laser processes but provided a new tool to study the dynamics of the laser material interaction itself which can greatly speed process development. Furthermore having this flexibility allows a single laser to cover a range of process parameters that heretofore normally required using several separate laser system. In this work we report on the application of temporal pulse shaping to CIGS P2 & P3 processing, CIGS P1 processing (molybdenum on glass), a-Silicon P1 processing (ZnO on glass), c-Silicon via hole drilling for emitter wrap through (EWT) and other processes using the PyroFlex 25 pulse programmable fiber laser. The temporal pulse shaping feature of the laser is demonstrated as a tool to probe the process dynamics and speed up the determination of optimal process parameters. When applicable, results between the pulse shape of a traditional laser and an optimized laser pulse shapes are compared.
This paper describes a robust mixed-synthesis controller for shape memory alloy (SMA) actuators. ... more This paper describes a robust mixed-synthesis controller for shape memory alloy (SMA) actuators. The weights for the controller are chosen such that the disturbance rejection criterion is met for low frequencies and robust stability is maintained for high frequencies. Simulation and experimental results show fast and accurate response for strain in the SMA under no perturbation. The performance of the
A computer vision system which performs real-time mode control of a high powered CO* laser has be... more A computer vision system which performs real-time mode control of a high powered CO* laser has been developed. The device continuously monitors the output beam to derive alignment data for the primary resonator optic. The technique ensures that the laser's intensity distribution is as uniform as possible. Valuable profile data and beam diagnostics are also generated by the system.
This paper describes a gain-scheduled controller for a shape memory alloy (SMA) actuator. For acc... more This paper describes a gain-scheduled controller for a shape memory alloy (SMA) actuator. For accurate control of an SMA actuator, it is important to develop a precise model for the SMA. A model has been proposed based on concepts from physics. The equations include Joules heating - convectional cooling to explain the dynamics of temperature, Fermi-Dirac statistics to explain the
ABSTRACT Laser surface texturing process involves creation of microfeatures, e.g., tiny dimples, ... more ABSTRACT Laser surface texturing process involves creation of microfeatures, e.g., tiny dimples, usually distributed in a certain pattern, covering only a fraction of the surface of the material that is being treated. The process offers several advantages for tribological applications, including improved load capacity, wear resistance, lubrication lifetime, and reduced friction coefficient. In the present study, the surface modification of gray cast iron, using millisecond (λ = 1,064 nm), nanosecond (λ = 1,064 nm) and femtosecond (λ = 800 nm) pulse duration laser irradiation, is adopted to establish a particular geometrical pattern with dimple features and dimensions, to improve wear and friction behavior. The effect of various laser processing parameters, including laser pulse energy, pulse duration and processing speed, on the performance characteristics of the laser-treated samples is investigated. The microtextured surfaces were produced on gray cast iron using different millisecond (0.5 ms), nanosecond (40 ns) and femtosecond (120 fs) laser source with the dimple depth between 3 and 15 μm. The coefficient of friction for the untextured surface was ~0.55, millisecond laser textured ~0.31, nanosecond laser textured ~0.02 and femtosecond laser ~0.01, under normal force of 50 N and sliding speed of 63 mm/s. Surface texturing of the gray cast iron surface using femtosecond pulse duration resulted in significant improvement in wear resistance in comparison to the untextured as well as millisecond and nanosecond laser-textured surface.
Ahstract : The usefulness of a particular type of dietary protein for a quicker acclimatization t... more Ahstract : The usefulness of a particular type of dietary protein for a quicker acclimatization to simulated high altitude stress was investigated in albino rats, by studying the changes occurring in the levels of urea cycle enzymes in liver. A good quality protein in (ega) and a ...
Changes in dietary protein quality and high altitude stress alter the serum urea cycle enzyme act... more Changes in dietary protein quality and high altitude stress alter the serum urea cycle enzyme activities. To find a dietary protein which will facilitate quicker acclimatization to altitude stress, groups of rats were fed two diets, isocaloric and isonitrogenous, but differing in amino acid make up. The rats were exposed to simulated altitude stress of 0.5 atmospheric pressure for various periods up to 65 h. When serum arginase and ornithine transcarbamylase activities were assayed, it was seen that the group on the unbalanced protein (Cajanus cajan) diet showed less increase on exposure and a tendency to return to normal level earlier than the group on the balanced protein (egg) diet.
Measurements of the electron density within a photo-initiated, impulse-enhanced, electrically exc... more Measurements of the electron density within a photo-initiated, impulse-enhanced, electrically excited (PIE) laser gas discharge are presented. Ion current measurements were made using a single Langmuir electrostatic probe positioned within the laser discharge volume. Calculations of the electron density were made utilizing a thick-sheath analysis. The results indicate that the electron density increases by two orders of magnitude as the pulser power level is increased. In addition, the electron density was observed to decrease markedly as the dc discharge current was increased.
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Papers by S. Nikumb