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

Abstract

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 laserinduced 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. Phys. 64(4), 1549-1554 (1976). 11. P. K. Kennedy, "A first-order model for computation of laser-induced breakdown thresholds in ocular and aqueous media. I. Theory," IEEE J. Quantum Electron. 31(12), 2241-2249 (1995). 12. D. X. Hammer, R. J. Thomas, G. D. Noojin, B. A. Rockwell, P. P. Kennedy, and W. P. Roach, "Experimental investigation of ultrashort pulse laser-induced breakdown thresholds in aqueous media," IEEE J. Quantum Electron. 32(4), 670-678 (1996). calculation of thresholds, absorption coefficients, and energy density," IEEE J. Quantum Electron. 35(8), 1156-1167 (1999

Interactive tissue reactions of 1064‐nm focused picosecond‐domain laser and dermal cohesive polydensified matrix hyaluronic acid treatment in in vivo rat skin

“…Although two passes of picosecond laser treatment at each experimental setting were delivered at 200‐msec intervals, the power density levels of picosecond laser treatments in our study were below the theoretical irradiation threshold for generating free seed electrons via multiphoton absorption5: In our study, we used power density settings for each microbeam of 3.1 × 10 10 W/cm 2 when using the MLA‐type handpiece and 1.1 × 10 11 W/cm 2 when using the DOE‐type handpiece. Additionally, picosecond laser treatment in the dual‐pulse mode delivered laser energy through two consecutive, 450‐psec pulses with a power density of 5.5 × 10 10 W/cm 2 /microbeam at a 1.5‐nsec inter‐pulse interval.…”

“…Picosecond laser‐induced micro‐injury zones present histologically as a few large, pseudo‐cystic vacuoles and/or numerous perinuclear microscopic vacuoles in the epidermis and upper dermis 2,6‐8. The generation of micro‐injury zones is initiated as the laser stimulates the production of free electrons via multiphoton absorption or thermionic emission, depending on the power density of the picosecond laser pulse and the absorption properties of chromophores in the target tissue 5. Theoretically, multiphoton absorption occurs in a chromophore‐independent manner at a higher irradiation threshold (~10 13 W/cm 2 in water) than thermionic emission, which occurs in a chromophore‐dependent manner at a relatively lower irradiation threshold 5…”

“…Picosecond‐domain laser treatment using a microlens array (MLA) or a diffractive optical element (DOE) has been shown to improve atrophic scars and wrinkles by generating micro‐injury zones in the epidermis, basement membrane, and upper dermis 1‐5. The histologic patterns of vacuolar changes resulting therefrom have been shown to depend on treatment settings, including the melanin index of the target tissue, the wavelength and power density of the picosecond laser, and the distance between the microlens and target tissue 6‐8.…”

Bubble dynamics of laser-induced cavitation in plasmonic gold nanorod solutions and the relative effect of surface tension and viscosity

“…The fluence required to form LIC bubbles is referred to as the LIB threshold. When the solution demonstrates a 50% probability of bubble formation at a certain fluence, this fluence is defined as the threshold fluence for bubble formation [21]. The plasma formation can be observed by eye since the luminescence appears as white bright light [21].…”

The role of morphology and coupling of gold nanoparticles in optical breakdown during picosecond pulse exposures

“…LIB is usually induced when the laser irradiance surpasses a certain threshold (which will henceforth be referred to as the “optical breakdown threshold”) and the free-electron density exceeds a critical value in the range of 10 18 –10 21 cm −3 [ 17 , 22 – 26 ]. The interaction of a strong electromagnetic field with a gold nanoparticle in an aqueous medium, which models a biological environment, can initiate breakdown (i) through multiphoton absorption and the tunneling effect, usually referred to as laser-induced optical breakdown (LIOB) [ 26 – 27 ]; (ii) through a thermal initiation pathway also known as laser-induced thermal breakdown (LITB) [ 28 – 29 ]; or (iii) through the photo-thermal emission of hot electrons off the surface of the nanoparticle [ 30 – 31 ]. After some seed electrons have been generated via a combination of the processes mentioned above, the plasma starts to gain sufficient kinetic energy from the laser pulse by inverse Bremsstrahlung absorption and grows through impact ionization known as electron avalanche [ 32 ].…”