Influence of the beam profile on laser-induced thresholds using explants

Scarlett Ramos; Philipp Elmlinger; Wilhelm Stork; Nico Heussner

doi:10.1117/12.2557057

2 April 2020 Influence of the beam profile on laser-induced thresholds using explants

Scarlett Ramos, Philipp Elmlinger, Wilhelm Stork, Nico Heussner

Proceedings Volume 11363, Tissue Optics and Photonics; 113631D (2020) https://doi.org/10.1117/12.2557057
Event: SPIE Photonics Europe, 2020, Online Only

Abstract

Previous studies determining laser-induced damage thresholds show inconsistent injury results due to measurement techniques as well as methodological challenges using top hat profiles. One reason that decisively influences the ED₅₀ value is the appearance of so-called intensity modulations of a top hat associated with the quality of the energy uniformity on the irradiated tissue sample. By using two different square core fiber lengths (2 m, 20 m) to produce a top hat, we can on one hand ensure the focus control and the correlated homogenized intensity distribution and on the other hand vary and determine intensity modulations in the profile. This means that the accuracy of the measurements is significantly enhanced and the influence of energy variations in the profile can be evaluated explicitly and quantitatively. Our laser-induced irradiation experiments were performed with 1.8 ns pulses at a wavelength of 532nm on porcine RPE by means of a Q-switched, frequency-doubling Nd:YAG laser. Intensity modulations are characterized by a modulation factor that describes the ratio of maximum irradiation to the average. The generated factors in our measurements are 1.78 (high intensity variation) and 1.15 (low intensity variation). The calculated ED₅₀ values are 52.15 μJ for the higher modulations and 33.90 μJ for the lower modulations inducing a discrepancy factor of 1.54. Hence, the determined thresholds highlight the importance of the influence of intensity modulations within the beam profile during irradiation. Therefore, we examine this influence and its possible consideration and handling with determined threshold data. Furthermore, a strategy for ensuring a high top hat quality for the assessment of prospective threshold data is shown.

Conference Presentation

Citation Download Citation

Scarlett Ramos, Philipp Elmlinger, Wilhelm Stork, and Nico Heussner "Influence of the beam profile on laser-induced thresholds using explants", Proc. SPIE 11363, Tissue Optics and Photonics, 113631D (2 April 2020); https://doi.org/10.1117/12.2557057

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