Dependence of retinal model temperature calculations on beam shape and absorption coefficients

A homogeneous, absorbing-layer thermal model of the retina is used to perform calculations of retinal temperature increases resulting from exposure to laser radiation. Comparisons are made between uniform rectangular and circularly symmetric Gaussian beam sources of equal power. Calculations are performed for a wide range of rectangular beam sizes and aspect ratios. The results indicate that temperature histories for rectangular and Gaussian beam sources have similar profiles. It is found numerically that the ratio of the temperature increases from the two different beam profiles is insensitive to the value of the absorption coefficient. It is also shown analytically that the ratio of the temperature time derivatives is independent of the absorption coefficient. Finally, in general, high (low) aspect ratio rectangular beams cause smaller (greater) temperature increases than a corresponding equal power Gaussian beam. These results are relevant in the determination of safety standards for diode laser sources which are capable of emitting high aspect ratio rectangularly shaped beams.