Ambient Pressure Laser Heating and Melting of Pt Foil—Validating BL Temperature Measurements Wed Feb 21-Fri Feb 23 Pt foil (4  m thin) cut in thin strip and mounted in “Wire melting chamber”. Chamber flooded with Ar gas. Laser Power setting at 25 Amps. Waveplate value upon melting Volts. This means the laser power at the sample was approx.5 Watts (combined upstream and downstream) Melt determination made by visual observation of “melt pool” and/or flicker of sample. Neutral density filters greatly aid in visual observations. Simultaneous diffraction aided in melt determination, but diffraction signal from sample after heating is very weak due to texturing. Detailed discussion of diffraction signal given below.

Pre&Post Heat Pt Foil ~25  m Post-heating observations support melting with appearance of holes in foil, and foil having a different (glassy?) texture. PreHeating PostHeating

Ambient Pressure Laser Heating and Melting of Pt Foil Temperature calculation is done by fitting data (corrected for system response) to the Planck function in a wavelength range of nm. No wavelength dependent emissivity was applied to the data. The melting temperature is calculated as the average of the last temperature when a “solid” observation is made and the first determination when a “melt” observation is made. For 3 separate runs with observations made both upstream and downstream, the average melt temperature is determined as 2052+/-29 K. This is close to the literature value of 2041 K.

Pt Foil Ambient P Laser Melting: Raw Data

Temperature Profile during melt observation of ambient pressure Pt foil

Temperature Vs Laser Power Temperature vs total power at sample position (upstream + downstream) Plot levels off at Pt Tm Another supporting piece of evidence for melt indication

Diffraction signal from Pt foil at ambient condition right after mounting foil before any heating 20 keV Dist: mm X-ray diffraction during laser heating of Pt foil

Diffraction signal almost completely disappears on a mm-area after heating to moderate temperatures (barely coupling). 1 single diffraction spot left.

Zoom in on diffraction spot

Most intense D-value corresponds to (111) of Pt. ~ 2.27 Å (unsure of why spot is split into 3 peaks) residual strain?

In vicinity of melting. Spot broadens and loses intensity

During Heating Room Temperature

Integrated Pt Spot During Heating  T =~2000K  ~1e-5  d/d ~ 2e-5 d ~ 2.25 => d +  d = Spot broadens and shifts to higher dsp. Confirms the alignment of x- ray and laser (diffraction from laser heated spot)

Peak sharpens up upon quenching.

After melting most intensity recovered to the lowest of the 3 peaks