Temperature dependence of nanosecond laser pulse thresholds of melanosome and microsphere microcavitation

Abstract

Abstract. Melanosome microcavitation is the threshold-level retinal pigment epithelium (RPE) damage mechanism for nanosecond (ns) pulse exposures in the visible and near-infrared (NIR). Thresholds for microcavitation of isolated bovine RPE melanosomes were determined as a function of temperature (20 to 85°C) using single ns laser pulses at 532 and 1064 nm. Melanosomes were irradiated using a 1064-nm Q-switched Nd:YAG (doubled for 532-nm irradiation). For comparison to melanosome data, a similar temperature (20 to 65°C) dependence study was also performed for 532 nm, ns pulse exposures of black polystyrene microbeads. Results indicated a decrease in the microcavitation average radiant exposure threshold with increasing sample temperature for both 532-and 1064-nm single pulse exposures of melanosomes and microbeads. Threshold data and extrapolated nucleation temperatures were used to estimate melanosome absorption coefficients in the visible and NIR, and microbead absorption coefficients in the visible, indicating that melanin is a better absorber of visible light than black polystyrene. The NIR melanosome absorption coefficients ranged from 3713 cm −1 at 800 nm to 222 cmat 1319 nm. These data represent the first temperature-dependent melanosome microcavitation study in the NIR and provide additional information for understanding melanosome microcavitation threshold dependence on wavelength and ambient temperature. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 UnportedLicense. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Incident Fluence Analysis for 755‐nm Picosecond Laser Treatment of Pigmented Skin Lesions Based on Threshold Fluences for Melanosome Disruption

“…Threshold fluences of short laser pulses with various widths have been investigated for selective melanosome response [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ], and the threshold fluences of femtosecond‐to‐microsecond laser pulses for melanosome disruption in laser skin treatment have been reported [ 10 , 11 ]. Such studies visually observed the disruption through the grossly apparent immediate whitening response of the skin surface from increased optical scattering.…”

“…Melanosome disruption from the net threshold fluences was not shown. Experimental analyses of picosecond‐to‐microsecond laser pulses in selective retina treatment have also been conducted using melanosomes isolated from porcine and bovine eyes [ 12 , 13 , 14 , 15 , 16 ]. However, these analyses investigated the threshold fluences for the microbubble formation around the melanosomes, overstretching the retinal pigment epithelium (RPE) cell membrane [ 17 ].…”

Direct numerical simulation of the initial stage of a thermally induced microcavitation in a water-rich biotissue triggered by a nanosecond pulsed laser

“…Schmidt et al investigated the microcavitation processes of retinal pigment epithelium melanosomes and polystyrene microspheres. [7][8][9] Most of these studies were based upon experimental methods and relied on fast laser imaging to capture the transient dynamics of the vapor bubble(s) under different laser, tissue, and event boundary conditions.…”