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首页> 外文会议>Society of Photo-Optical Instrumentation Engineers Conference on Laser Interaction with Tissue and Cells >Multiphoton absorption is probably not the primary threshold damage mechanism for femtosecond laser pulse exposures in the retinal pigment epithelium
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Multiphoton absorption is probably not the primary threshold damage mechanism for femtosecond laser pulse exposures in the retinal pigment epithelium

机译：多光子吸收可能不是视网膜颜料上皮中飞秒激光脉冲暴露的主要阈值损伤机制

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Laser induced breakdown has the lowest energy threshold in the femtosecond domain, and is responsible for production of threshold ocular lesions. It has been proposed that multiphoton absorption may also contribute to ultrashort-pulse tissue damage, based on the observation that 33 fs, 810 nm pulse laser exposures caused more DNA breakage in cultured, primary RPE cells, compared to CW laser exposures delivering the same average power. Subsequent studies, demonstrating two-photon excitation of fluorescence in isolated RPE melanosomes, appeared to support the role of multiphoton absorption, but mainly at suprathreshold irradiance. Additional experiments have not found a consistent difference in the DNA strand breakage produced by ultrashort and CW threshold exposures. DNA damage appears to be dependent on the amount of melanin pigmentation in the cells, rather than the pulsewidth of the laser; current studies have found that, at threshold, CW and ultrashort pulse laser exposures produce almost identical amounts of DNA breakage. A theoretical analysis suggests that the number of photons delivered to the RPE melanosome during a single 33-fsec pulse at the ED_(50) irradiance is insufficient to produce multiphoton excitation. This result appears to exclude the melanosome as a locus for two- or three-photon excitation; however, a structure with a larger effective absorption cross-section than the melanosome may interact with the laser pulses. One possibility is that the nuclear chromatin acts as a unit absorber of photons resulting in DNA damage, but this does not explain the near equivalence of ultrashort and CW exposures in the comet assay model. This equivalence indicates that multiphoton absorption is not a major contributor to the ultrashort pulse laser damage threshold in the near infrared.
机译：激光感应击穿具有飞秒域中的最低能量阈值，并且负责生产阈值眼病变。已经提出，多相吸收也可能有助于超短脉冲组织损伤，基于33 fs，810nm脉冲激光曝光引起培养的初级RPE细胞中的更多DNA断裂，与CW激光照射相同的平均值相比力量。随后的研究，展示了分离的RPE黑色素中的荧光激发的两光晶激发，似乎支持多感测吸收的作用，但主要是在Suprathreshold辐照度下。另外的实验并未发现通过超短和CW阈值曝光产生的DNA链断裂差异。 DNA损伤似乎取决于细胞中黑色素色素沉着的量，而不是激光的脉冲宽;目前的研究发现，在阈值，CW和超短脉冲激光曝光时产生几乎相同的DNA断裂。理论分析表明，在ED_（50）辐照度下的单个33-FSEC脉冲期间递送到RPE丝体组的光子的数量不足以产生多光子激发。该结果似乎将黑色素体排除为两个或三光子励磁的基因座;然而，具有比黑色素组更大的有效吸收横截面的结构可以与激光脉冲相互作用。一种可能性是核染色质作作为光子的单位吸收器，导致DNA损伤，但这并未解释彗星测定模型中超短的近乎曝光和CW暴露的接近等价。此等效表明多光音吸收不是近红外线中超短脉冲激光损伤阈值的主要贡献者。

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