Update on Armor Simulation Experiments At Dragonfire Facility Farrokh Najmabadi and John Pulsifer HAPL Meeting November 8-9, 2005 University of Rochester Electronic copy: UCSD IFE Web Site:

Experimental Setup High-Temperature Sample holder Thermometer head QCM RGA Laser entrance

Plans from the last Meeting 1) Error in Temperature Measurement: Thermometer is calibrated based on melting point of W (3,700K). This leads to relatively larger errors (~10-15%) in lower temperatures (~2,000-2,500 o C). At present, thermometer cannot measure temperature below ~2,000 o C  Above issues will be addressed before next set of runs: Upgrade of the thermometer (Absolute calibration, lower temperature) In-vacuum re-positioning of laser imprint/thermometer 2) Profilometry of treated sample 3) Test samples at lower temperature (i.e., lower laser energy) 4) Test sample with He from UW 1) Error in Temperature Measurement: Thermometer is calibrated based on melting point of W (3,700K). This leads to relatively larger errors (~10-15%) in lower temperatures (~2,000-2,500 o C). At present, thermometer cannot measure temperature below ~2,000 o C  Above issues will be addressed before next set of runs: Upgrade of the thermometer (Absolute calibration, lower temperature) In-vacuum re-positioning of laser imprint/thermometer 2) Profilometry of treated sample 3) Test samples at lower temperature (i.e., lower laser energy) 4) Test sample with He from UW

Thermometer Calibration

History of Thermometer Calibration Issues  Development of single-fiber based thermometer coincided with rebuilt of our laser and reduction of laser output to achieve a smoother spatial profiles.  Afterwards only one flat region was observed in T vs E measurements.  The thermometer was giving the maximum temperature of about 5,000K for the flat region (W melting= 3,700K, evaporation = 6,000K).  It was assumed that thermometer calibration at low frequencies (mechanical chopper) should be different than high-frequency response needed for laser irradiation.  Could not find a way to calibrate at higher frequencies.  Development of single-fiber based thermometer coincided with rebuilt of our laser and reduction of laser output to achieve a smoother spatial profiles.  Afterwards only one flat region was observed in T vs E measurements.  The thermometer was giving the maximum temperature of about 5,000K for the flat region (W melting= 3,700K, evaporation = 6,000K).  It was assumed that thermometer calibration at low frequencies (mechanical chopper) should be different than high-frequency response needed for laser irradiation.  Could not find a way to calibrate at higher frequencies. Early measurements of temperature rise versus laser energy (multiple- fiber based thermometer). The two flat regions were identified as melting and evaporation regions. Early measurements of temperature rise versus laser energy (multiple- fiber based thermometer). The two flat regions were identified as melting and evaporation regions.

 Detailed modeling indicates that: 1)Thermometer will not see the melting Plateau (duration is too short). 2)Large sublimation above the melting point. Calculation from R. Raffray with a 8ns square pulse  Detailed modeling indicates that: 1)Thermometer will not see the melting Plateau (duration is too short). 2)Large sublimation above the melting point. Calculation from R. Raffray with a 8ns square pulse Absolute Calibration Is Now Achieved  Managed to reduce the light pulses from chopper wheel to ~100  s intervals.  Thermometer calibration was checked against an electronic camera flash (10-20  s, ~5,500K).  Temperature measurement as low as 1,500K was achieved with thermometer in mid-gain (1,000K reading with high gain is expected).  Managed to reduce the light pulses from chopper wheel to ~100  s intervals.  Thermometer calibration was checked against an electronic camera flash (10-20  s, ~5,500K).  Temperature measurement as low as 1,500K was achieved with thermometer in mid-gain (1,000K reading with high gain is expected).

Measured Temperature Rise in W Ramp down experiments in air Thermometer: Low-gain Signal is small “Ramp down experiment”: Laser energy was raised to its larger value and then lowered gradually with temperature measurement at various points.

Measured Temperature Rise in W Ramp down experiments in air Thermometer: Low-gain Long term exposure runs Thermometer: Mid-gain  For temperatures below the melting point,  T/E  11 K/mJ

Measured Temperature Rise in W Ramp down experiments in air Thermometer: Low-gain Long term exposure runs Thermometer: Mid-gain Ramp down experiments in rough vacuum Thermometer: Mid-gain  In the last set of data (red squares), the signal strength drops significantly (similar to long term exposure runs) indicating a temperature drop by a factor of 3, but ratios of 800nm/700nm wavelengths gives a much lower temperature drop.

Profilometry of Treated Samples All quoted final temperatures assume  T/E  11 K/mJ except for samples 11 & 12 (direct measurements)

Fresh samples are quite smooth  Reported values in the following viewgraphs are 1.Rq: maximum deviation of the red line 2.Peak to valley  Reported values in the following viewgraphs are 1.Rq: maximum deviation of the red line 2.Peak to valley

Profilometry of Sample 8, 370 mJ, 600 o C (Final: 4,900 o C?) 10 3 shots 10 5 shots 10 4 shots 1000 nm 2,000 nm  Sample area appears to bulge outward at lower shot rates and a large “hole” (13  m deep) appears at 10 5 shots.

Profilometry of Sample 7, 240 mJ, 600 o C (Final: 3,500 o C?)  Sample area appears to bulge outward at lower shot rates and a small “hole” is appearing at 10 5 shots shots 10 5 shots 10 4 shots 500 nm 1000 nm 3000 nm

Profilometry of Sample 7, 240 mJ, 600 o C (Final: 3,500 o C?) 10 3 shots 10 5 shots 10 4 shots

Profilometry of Sample 10, 370 mJ, 100 o C (Final: 4,400 o C?) 10 3 shots 10 5 shots 10 4 shots  Similar to sample 7 (370 mJ, 600 o C) sample area bulges outward at lower shot rates and a large “hole” (4  m deep) appears at 10 5 shots nm 4000 nm 500 nm

Profilometry of Sample 11, 200 mJ, 500 o C (Final: 2,980 o C?) 10 3 shots 10 5 shots 10 4 shots 500 nm 1000 nm

Profilometry of Sample 12, 100 mJ, 500 o C (Final: 1,880 o C?) 10 5 shots  No visible mark on the sample after 10 3 or 10 4 shots. We could not find the exposure location to perform profilometry.  Rq of this sample is similar to a unexposed sample (~ 30 nm). However peak-to- valley roughness is increased by a factor of 3-4.  No visible mark on the sample after 10 3 or 10 4 shots. We could not find the exposure location to perform profilometry.  Rq of this sample is similar to a unexposed sample (~ 30 nm). However peak-to- valley roughness is increased by a factor of 3-4.

Profilometry of Treated Samples  Rq is increasing almost linearly with number of shots for S10 and S8 (both estimated to be above melting)  Rq appears to saturate for other samples (however pictures indicate a shift from a bugle out to a “hole”!)  Rq is increasing almost linearly with number of shots for S10 and S8 (both estimated to be above melting)  Rq appears to saturate for other samples (however pictures indicate a shift from a bugle out to a “hole”!) Ave. Rq for a fresh sample is ~ 30 nm.

Profilometry of Treated Samples  Peak to valley “roughness” is increasing almost linearly with number of shots for S10 and S8 (both estimated to be above melting)  It is not clear if Peak to valley “roughness” is saturating for other samples  Peak to valley “roughness” is increasing almost linearly with number of shots for S10 and S8 (both estimated to be above melting)  It is not clear if Peak to valley “roughness” is saturating for other samples

Summary and Plans 1) Thermometer Calibration Thermometer is calibrated absolutely and calibration is interpedently verified. At present, thermometer can measure temperatures to ~1,500K at mid-gain. (temperature measurement of 1,000K at high gain is expected). 2) Profilometry of treated samples was performed More exposure test at lower temperature (i.e., lower laser energy) and and/or intermediate and higher shots rates needed to make any conclusions. 3) Experimental setup QMS was operational during exposure of samples 11 & 12 and did not detect any material.  T vs E “anomalous” behavior in ramp-down experiment should be understood. In-vacuum re-positioning of laser imprint/thermometer Repeating exposure experiment with KrF laser 4) Test sample with He from UW 1) Thermometer Calibration Thermometer is calibrated absolutely and calibration is interpedently verified. At present, thermometer can measure temperatures to ~1,500K at mid-gain. (temperature measurement of 1,000K at high gain is expected). 2) Profilometry of treated samples was performed More exposure test at lower temperature (i.e., lower laser energy) and and/or intermediate and higher shots rates needed to make any conclusions. 3) Experimental setup QMS was operational during exposure of samples 11 & 12 and did not detect any material.  T vs E “anomalous” behavior in ramp-down experiment should be understood. In-vacuum re-positioning of laser imprint/thermometer Repeating exposure experiment with KrF laser 4) Test sample with He from UW