47 research outputs found
Resonant holographic interferometry of laserâablation plumes
Twoâdimensional speciesâresolved, holographic interferometry has been used to measure absoluteâlineâdensity profiles of KrF laser ablation plumes in vacuum and gas. Laser ablation plumes are generated by focusing a KrF excimer laser (40 ns, 248 nm, â€0.8 J) on a solid aluminum target at a fluence of 2â5 J/cm2. Aluminum neutral absoluteâlineâdensity profiles are measured to characterize the interaction of ablated material with background gases versus vacuum. The interferograms are made using a 20 ns pulsed dye laser tuned near (â€Â±0.020 nm) the 394.401 nm aluminum neutral transition from the ground state. Calculations have been performed to obtain absoluteâlineâdensity profiles from the resonant fringe shift data. Peak aluminum neutral line densities of up to 1Ă1015 cmâ2 have been measured for plumes in backgrounds of 14 mTorr and 1 Torr argon and in vacuum.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71215/2/APPLAB-63-7-888-1.pd
Laser diagnostic experiments on KrF laser ablation plasmaâplume dynamics relevant to manufacturing applications@f|
A brief review is given of the potential applications of laser ablation in the automotive and electronics manufacturing industries. Experiments are presented on KrF laser ablation of three materials relevant to manufacturing applications: aluminum metal vs aluminumânitride (AlN) and alumina (Al2O3) ceramics. Plasma and neutralâatom diagnostic data are presented from resonantâholographicâinterferometry, dyeâlaserâresonanceâabsorption photography, and HeNe laser deflection. Data show that plasma electron densities in excess of 1018 cmâ3 exist in the ablation of AlN, with lower densities in Al and Al2O3. Aluminum neutral and ion expansion velocities are in the range of cm/ÎŒs. Ambipolar electric fields are estimated to be 5â50 V/cm.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71186/2/PHPAEN-1-5-1619-1.pd
Resonantâholographicâinterferometry for absolute measurements of excimer laserâablated neutralâatom plume lineâdensity profiles
Experiments have been performed to measure Al neutral atom absolute lineâdensity profiles using resonantâholographicâinterferometry. The ablation source is a KrF excimer laser with a perâpulse energy of about 0.8 J. Targets are either pure aluminum or Al2O3. Aluminum groundâstate neutral atom lineâdensities are probed by a dye laser tuned near the 394.401 nm line. A doubleâpulse interferometry technique is employed in which one pulse includes the laser ablation plume and a second pulse generates reference fringes on a holographic plate by rotating a mirror. Holograms are reconstructed to give interference fringes on film by using a heliumâneon laser. Interferograms of laser ablated Al metal give maximum Al neutral plume lineâdensities in the range of 4â10Ă104 cmâ2. Aluminum neutral lineâdensities from Al2O3 targets are as much as 10â20 times larger than from Al metal targets. The sensitivity of this resonant diagnostic is 4 to 5 orders of magnitude higher than nonresonant neutralâparticle interferometry and may be adjusted by tuning the dye laser wavelength shift away from the resonance line. This diagnostic has been demonstrated in vacuum, gas (14 mTorr â 35 Torr) and RF plasma (30 mTorr â 1 Torr) environments. At higher gas pressures, the nonresonant gasâdynamic fringe shift can be subtracted to give the resonant fringe shift and species density.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87415/2/421_1.pd
Schlieren and dye laser resonance absorption photographic investigations of KrF excimer laserâablated atoms and molecules from polyimide, polyethyleneterephthalate, and aluminum
Hydrodynamic phenomena from KrF excimer laser ablation (10â3â20 J/cm2) of polyimide, polyethyleneterephthalate, and aluminum are diagnosed by schlieren photography, shadowgraphy, and dye laser resonance absorption photography (DLRAP). Experiments were performed both in vacuum and gaseous environments (10â5â760 Torr air, nitrogen, and argon). In vacuum, ablation plumes are observed to expand like a reflected rarefaction wave. As the background gas pressure is increased, shock waves and reducedâdensity ablation plumes become visible. Below 10 Torr, the ablation plume follows closely behind the shock wave. Between 20 and 100 Torr, the plume recedes behind the shock wave. Below 10 Torr and above about 200 Torr, both the plume and the shock expand with the same temporal power law dependence. Agreement is found between these power law dependences and those predicted by ideal blast wave theory. The DLRAP diagnostic clearly shows that the ablated material (CN molecule from polyimide and ground state neutral aluminum atoms from laserâablated aluminum) resides in the ablation plume. CN molecules are detected in both argon and air environments proving that CN is generated as an ablation product and not by reaction with the background gas. As the background gas pressure and the time after ablation is increased, the film darkening due to the laserâablated material begins to fade leaving only the nonresonant shadowgraphy component of the plume. The plume dynamics observed by DLRAP are discussed in terms of gas dynamics, plume chemical kinetics, material diffusion in the plume, and cluster/particulate formation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70260/2/JAPIAU-72-5-1696-1.pd
Resonant holographic interferometry measurements of laser ablation plumes in vacuum, gas, and plasma environments
Resonant holographic interferometry and dyeâlaserâresonanceâabsorption photography have been utilized to investigate the expansion of the laser ablation plumes produced by a KrF excimer laser beam (248 nm) focused onto an aluminum target (â0.1 cm2, 2â6 J/cm2). Plume expansion was studied in vacuum and in background argon gas pressures of 14 mTorr, 52 mTorr, 210 mTorr, 1 Torr, and 35 Torr. The existing theory for the interpretation of resonant interferograms has been extended to account for Doppler shift effects, the diagnostic laser bandwidth, and the selective absorption of the laser beam. Absolute line densities in the range 4.3Ă1013â1.0Ă1015 cmâ2 have been measured in the ablation plumes, which imply measured Al neutral densities of up to 1Ă1015 cmâ3. The total number of Al neutral atoms in a plume has been measured to be â3Ă1014, which corresponds to a surface etch rate of â1 nm/pulse. Expansion velocities in the range 1.1â1.4 cm/ÎŒs were measured for the pressures â€210 mTorr, while â0.3 cm/ÎŒs was measured for 1 Torr and â0.08 cm/ÎŒs was measured for 35 Torr. Ablation plume expansion into a 1 Torr rf argon plasma environment was compared with the expansion into a 1 Torr argon gas. The ablation plume appeared to expand and dissipate slightly faster in the plasma.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70791/2/JAPIAU-76-9-5457-1.pd
Copper vapor laser machining of polyimide and polymethylmethacrylate in atmospheric pressure air
A repetitively pulsed copper vapor laser (510 and 578 nm) is used to machine an opaque polymer (polyimideâVespel) and a transparent polymer (polymethylmethacrylateâLucite). Lucite is machinable by coating the surface with an ink which is semiâopaque to the green and yellow laser light. The repetition rate of the laser was 10 kHz with approximately 0.35 mJ/pulse and 3.5 W average power at the copper vapor laser wavelengths for a pulse width of 40 ns. The copper vapor laser thermally loads the target, generating thermal waves and sound waves in the gas which are investigated using HeNe laser beam deflection. The gas adjacent to the target is heated to steady state on the order of 100â400 s. Above the etching threshold, at approximately 10 mJ/cm2/pulse, the target is rapidly machined: 2âmmâdiam, 2âmmâdeep holes are drilled in 300 s in Vespel. At higher fluences of 100â150 mJ/cm2/pulse in 760 Torr of air it takes 180 s to bore through a 2âmmâthick disk of Vespel. The machined surfaces of the two polymers are very different. Machined Vespel samples are charred and cratered, whereas the Lucite samples show evidence of melting with little charring. The machining of polymers by visibleâlight copper vapor lasers is being compared to UV photoablation by KrF excimer laser light in order to study thermal versus nonthermal etching mechanisms.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71173/2/JAPIAU-72-7-3080-1.pd
Effect of SGLT2 inhibitors on stroke and atrial fibrillation in diabetic kidney disease: Results from the CREDENCE trial and meta-analysis
BACKGROUND AND PURPOSE: Chronic kidney disease with reduced estimated glomerular filtration rate or elevated albuminuria increases risk for ischemic and hemorrhagic stroke. This study assessed the effects of sodium glucose cotransporter 2 inhibitors (SGLT2i) on stroke and atrial fibrillation/flutter (AF/AFL) from CREDENCE (Canagliflozin and Renal Events in Diabetes With Established Nephropathy Clinical Evaluation) and a meta-Analysis of large cardiovascular outcome trials (CVOTs) of SGLT2i in type 2 diabetes mellitus. METHODS: CREDENCE randomized 4401 participants with type 2 diabetes mellitus and chronic kidney disease to canagliflozin or placebo. Post hoc, we estimated effects on fatal or nonfatal stroke, stroke subtypes, and intermediate markers of stroke risk including AF/AFL. Stroke and AF/AFL data from 3 other completed large CVOTs and CREDENCE were pooled using random-effects meta-Analysis. RESULTS: In CREDENCE, 142 participants experienced a stroke during follow-up (10.9/1000 patient-years with canagliflozin, 14.2/1000 patient-years with placebo; hazard ratio [HR], 0.77 [95% CI, 0.55-1.08]). Effects by stroke subtypes were: ischemic (HR, 0.88 [95% CI, 0.61-1.28]; n=111), hemorrhagic (HR, 0.50 [95% CI, 0.19-1.32]; n=18), and undetermined (HR, 0.54 [95% CI, 0.20-1.46]; n=17). There was no clear effect on AF/AFL (HR, 0.76 [95% CI, 0.53-1.10]; n=115). The overall effects in the 4 CVOTs combined were: Total stroke (HRpooled, 0.96 [95% CI, 0.82-1.12]), ischemic stroke (HRpooled, 1.01 [95% CI, 0.89-1.14]), hemorrhagic stroke (HRpooled, 0.50 [95% CI, 0.30-0.83]), undetermined stroke (HRpooled, 0.86 [95% CI, 0.49-1.51]), and AF/AFL (HRpooled, 0.81 [95% CI, 0.71-0.93]). There was evidence that SGLT2i effects on total stroke varied by baseline estimated glomerular filtration rate (P=0.01), with protection in the lowest estimated glomerular filtration rate (45 mL/min/1.73 m2]) subgroup (HRpooled, 0.50 [95% CI, 0.31-0.79]). CONCLUSIONS: Although we found no clear effect of SGLT2i on total stroke in CREDENCE or across trials combined, there was some evidence of benefit in preventing hemorrhagic stroke and AF/AFL, as well as total stroke for those with lowest estimated glomerular filtration rate. Future research should focus on confirming these data and exploring potential mechanisms
Canagliflozin and Renal Outcomes in Type 2 Diabetes and Nephropathy
BACKGROUND Type 2 diabetes mellitus is the leading cause of kidney failure worldwide, but few effective long-term treatments are available. In cardiovascular trials of inhibitors of sodiumâglucose cotransporter 2 (SGLT2), exploratory results have suggested that such drugs may improve renal outcomes in patients with type 2 diabetes. METHODS In this double-blind, randomized trial, we assigned patients with type 2 diabetes and albuminuric chronic kidney disease to receive canagliflozin, an oral SGLT2 inhibitor, at a dose of 100 mg daily or placebo. All the patients had an estimated glomerular filtration rate (GFR) of 30 to 300 to 5000) and were treated with reninâangiotensin system blockade. The primary outcome was a composite of end-stage kidney disease (dialysis, transplantation, or a sustained estimated GFR of <15 ml per minute per 1.73 m 2), a doubling of the serum creatinine level, or death from renal or cardiovascular causes. Prespecified secondary outcomes were tested hierarchically. RESULTS The trial was stopped early after a planned interim analysis on the recommendation of the data and safety monitoring committee. At that time, 4401 patients had undergone randomization, with a median follow-up of 2.62 years. The relative risk of the primary outcome was 30% lower in the canagliflozin group than in the placebo group, with event rates of 43.2 and 61.2 per 1000 patient-years, respectively (hazard ratio, 0.70; 95% confidence interval [CI], 0.59 to 0.82; P=0.00001). The relative risk of the renal-specific composite of end-stage kidney disease, a doubling of the creatinine level, or death from renal causes was lower by 34% (hazard ratio, 0.66; 95% CI, 0.53 to 0.81; P<0.001), and the relative risk of end-stage kidney disease was lower by 32% (hazard ratio, 0.68; 95% CI, 0.54 to 0.86; P=0.002). The canagliflozin group also had a lower risk of cardiovascular death, myocardial infarction, or stroke (hazard ratio, 0.80; 95% CI, 0.67 to 0.95; P=0.01) and hospitalization for heart failure (hazard ratio, 0.61; 95% CI, 0.47 to 0.80; P<0.001). There were no significant differences in rates of amputation or fracture. CONCLUSIONS In patients with type 2 diabetes and kidney disease, the risk of kidney failure and cardiovascular events was lower in the canagliflozin group than in the placebo group at a median follow-up of 2.62 years
Canagliflozin and renal outcomes in type 2 diabetes and nephropathy
BACKGROUND Type 2 diabetes mellitus is the leading cause of kidney failure worldwide, but few effective long-term treatments are available. In cardiovascular trials of inhibitors of sodiumâglucose cotransporter 2 (SGLT2), exploratory results have suggested that such drugs may improve renal outcomes in patients with type 2 diabetes. METHODS In this double-blind, randomized trial, we assigned patients with type 2 diabetes and albuminuric chronic kidney disease to receive canagliflozin, an oral SGLT2 inhibitor, at a dose of 100 mg daily or placebo. All the patients had an estimated glomerular filtration rate (GFR) of 30 to <90 ml per minute per 1.73 m2 of body-surface area and albuminuria (ratio of albumin [mg] to creatinine [g], >300 to 5000) and were treated with reninâangiotensin system blockade. The primary outcome was a composite of end-stage kidney disease (dialysis, transplantation, or a sustained estimated GFR of <15 ml per minute per 1.73 m2), a doubling of the serum creatinine level, or death from renal or cardiovascular causes. Prespecified secondary outcomes were tested hierarchically. RESULTS The trial was stopped early after a planned interim analysis on the recommendation of the data and safety monitoring committee. At that time, 4401 patients had undergone randomization, with a median follow-up of 2.62 years. The relative risk of the primary outcome was 30% lower in the canagliflozin group than in the placebo group, with event rates of 43.2 and 61.2 per 1000 patient-years, respectively (hazard ratio, 0.70; 95% confidence interval [CI], 0.59 to 0.82; P=0.00001). The relative risk of the renal-specific composite of end-stage kidney disease, a doubling of the creatinine level, or death from renal causes was lower by 34% (hazard ratio, 0.66; 95% CI, 0.53 to 0.81; P<0.001), and the relative risk of end-stage kidney disease was lower by 32% (hazard ratio, 0.68; 95% CI, 0.54 to 0.86; P=0.002). The canagliflozin group also had a lower risk of cardiovascular death, myocardial infarction, or stroke (hazard ratio, 0.80; 95% CI, 0.67 to 0.95; P=0.01) and hospitalization for heart failure (hazard ratio, 0.61; 95% CI, 0.47 to 0.80; P<0.001). There were no significant differences in rates of amputation or fracture. CONCLUSIONS In patients with type 2 diabetes and kidney disease, the risk of kidney failure and cardiovascular events was lower in the canagliflozin group than in the placebo group at a median follow-up of 2.62 years