Influence of absorption induced thermal initiation pathway on irradiance threshold for laser induced breakdown.

Babu Varghese,Rieko Verhagen,Jonathan Palero,Valentina Bonito,Margaret Horton,Martin Jurna

doi:10.1364/boe.6.001234

Babu Varghese, Rieko Verhagen + Show 4 more

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https://doi.org/10.1364/boe.6.001234

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Abstract

We investigated the influence of thermal initiation pathway on the irradiance threshold for laser induced breakdown in transparent, absorbing and scattering phantoms. We observed a transition from laser-induced optical breakdown to laser-induced thermal breakdown as the absorption coefficient of the medium is increased. We found that the irradiance threshold after correction for the path length dependent absorption and scattering losses in the medium is lower due to the thermal pathway for the generation of seed electrons compared to the laser-induced optical breakdown. Furthermore, irradiance threshold gradually decreases with the increase in the absorption properties of the medium. Creating breakdown with lower irradiance threshold that is specific at the target chromophore can provide intrinsic target selectivity and improve safety and efficacy of skin treatment methods that use laser induced breakdown.

Highlights

The spectrum of laser based skin rejuvenation methods based on selective photothermolysis ranges from ablative to non-ablative, and more recently to fractional resurfacing
We demonstrate that the thermal initiation pathway used for generating seed electrons in thermal breakdown results in a lower irradiance threshold compared to multiphoton initiation pathway used for optical breakdown
Depending on the absorption properties of the medium three different breakdown regimes can be observed: (i) in the regime of lowest absorption laser induced optical breakdown occurs through multiphoton-initiation and irradiance threshold for optical breakdown is less dependent on the absorption properties of the medium compared to the high-absorption regime occurring through thermal breakdown; (ii) in the regime of medium to high absorption

Summary

Introduction

The spectrum of laser based skin rejuvenation methods based on selective photothermolysis ranges from ablative to non-ablative, and more recently to fractional resurfacing. The optical breakdown caused by tightly focused nearinfrared laser pulses in a grid of intradermal lesions leads to skin rejuvenation without affecting the epidermis [2]. This skin rejuvenation technique using laser induced optical breakdown has been indicated a strong potential for wrinkle and fine-line reduction [3]. Laser induced optical breakdown (LIOB) is a non-linear absorption process leading to plasma formation at locations where the irradiance threshold for breakdown is surpassed [4,5,6]. Laser induced optical breakdown (LIOB) via multiphoton absorption occurs when the irradiance threshold of ~1013 W/cm is surpassed in the focal region. Breakdown through the thermionic emission pathway starts with the linear absorption of energy, which is later followed by non-linear absorption via avalanche ionization

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