Numerical calculations of the temperature distribution and the cooling speed in the laser-heated diamond anvil cell

Abstract

Numerical calculations have been done to reveal temperature distributions and cooling speeds of laser-heated samples in a diamond anvil cell. The distributions were calculated for variable experimental parameters including the diameter of the laser beam, anvil gap, and sample. The results show that the radial temperature distribution in all samples is Gaussian. The axial temperature gradient is ∼10 K/μm in samples heated by a broad laser beam of 100 μm diameter, and is ∼102 K/μm when a narrow laser beam of 10 μm diameter is used. The broad beam can generate a less extreme temperature gradient in both radial and axial directions as compared with the narrow beam, whereas the temperature gradient strongly depends on the anvil gap, although this is minimized when a narrow beam is used. When the narrow beam is used to heat samples, the surface temperature of the anvil culet can be kept below 400 K; thus, the narrow beam is suitable for heating samples under high pressure while keeping anvil temperatures low. Cooling speeds of the laser-heated samples were found to be from 100 to 102 K/μs. The discrepancy between actual sample temperature and measured temperature was also evaluated. To measure the peak temperature of a sample heated by a laser with a Gaussian power distribution within 5% accuracy, radiation from a circular area of less than (1/2)σ of the Gaussian must be observed.