Paper Review

Paper Review

4. Retinal dose response from exposure to the supercontinuum generated by a near-infrared femtosecond laser

Xomalin G. Peralta [a], Joseph E. Clary [a], Amanda M. Peterson [a], Matthew E. Macasadia [a], Harvey M. Hodnett [a], Maximillian V. Hart [a], Amanda J. Tijerina [b], Gary D. Noojin [a], Semih Kumru [c], Francesco J. Echeverria [a], Charles Schwarten [a], Emily M. Corbin [a], Emily N. Boice [c]*

[a] SAIC, 4141 Petroleum Rd., JBSA Fort Sam Houston, Texas 78234, USA [b] Conceptual MindWorks, Inc., JBSA Fort Sam Houston, Texas 78234, USA [c] Air Force Research Laboratory, 711th Human Performance Wing, Human Effectiveness Directorate, Bioeffects Division, Optical Radiation Branch, JBSA Fort Sam Houston, Texas 78234, USA

Journal of Laser Applications [Published: 2026] 

This study investigates the ocular safety risks posed by nonlinear optical effects when the human eye is exposed to ultrashort near-infrared (NIR) femtosecond laser pulses. While current laser safety standards (ANSI Z136.1-2022) establish maximum permissible exposures (MPE) for various wavelengths, they do not account for the generation of a supercontinuum—a broadband white light produced when high-peak-power pulses interact with the eye's aqueous media. Using Yucatan mini pig models, the researchers measured the median effective dose ($ED_{50}$) for retinal damage caused by single ~100 fs pulses at wavelengths of 1325, 1350, and 1375 nm.

A critical finding of the study is that supercontinuum generation occurs even at energy levels previously considered safe by point-source MPE standards. During exposure, bright flashes were consistently observed in the retinal images, confirming the conversion of NIR photons into visible light within the vitreous humor. The experimental results revealed that the $ED_{50}$ values for 1350 nm and 1375 nm were significantly lower than the established MPE limits, with the $ED_{50}$ to MPE ratio for 1375 nm being as low as 0.08. This indicates that the current safety guidelines may not be sufficiently protective against the damaging effects of nonlinear interactions.

Furthermore, histological analysis of the resulting retinal lesions confirmed severe structural damage, including pyknotic outer nuclear cells, withered photoreceptors, and the loss of retinal pigment epithelium (RPE) cells. Probit analysis was utilized to accurately extract the damage thresholds, showing that retinal alterations appear as faint white or pink circular spots at the point of exposure. The data suggests that biological variability and the unique nonlinear refractive index of the eye's internal media play a larger role in laser-induced injury than previously assumed.

In conclusion, the study successfully demonstrates that NIR femtosecond lasers can cause unforeseen retinal damage due to nonlinear optical effects. These findings provide a vital empirical basis for the international laser safety community to re-evaluate and potentially revise current MPE standards to better protect against ultrashort pulse durations in biomedical and industrial applications.

Seong-Uk Heo [a], Ji-Hyun Kim [b], Seong Yong Oh [c], Gwon Lim [c], Sungmo Nam [c], TaekSoo Kim [c], Hyunmin Park [c], Chul-Woo Chung [a*]

[a] Division of Architectural and Fire Protection Engineering, Pukyong National University, Yongso-ro 45, Nam-gu, Busan 48513, Republic of Korea

[b] Multidisciplinary Infra-Technology Research Laboratory, Pukyong National University, Yongso-ro 45, Nam-gu, Busan 48513, Republic of Korea

[c] Laser Application Research Team, Korea Atomic Energy Research Institute, Daedeok-daero 989beon-gil 111, Yuseong-gu, Daejeon 34057, Republic of Korea 

Case Studies in Construction Materials IF: 6.6 [Published: 2022] 

This study investigates the feasibility and optimal conditions for using laser scabbling to decontaminate concrete surfaces during the decommissioning of nuclear power plants. Utilizing a high-power 5 kW fiber laser with an extended stand-off distance of 900 mm, the researchers systematically examined how the internal moisture content and the mix proportion of concrete affect the efficiency of the material removal process.

A critical finding of the study is that internal moisture is an absolute prerequisite for successful laser scabbling. When the process was tested on oven-dry (OD) concrete, it was highly inefficient, resulting in a minimal weight loss of only 0.26%. Without free water available to evaporate, the laser energy continuously heated the surface to a maximum of $1420^{\circ}C$. This extreme heat caused the siliceous fine aggregate to vitrify—melting into an amorphous glass—rather than safely breaking apart. Conversely, air-dry (AD) and saturated surface-dry (SSD) concretes demonstrated excellent scabbling efficiency, achieving weight losses of 6.17% and 5.68%, respectively. In these moist conditions, the evaporation of free water consumes surface energy and builds internal vapor pressure. This internal pressure physically fractures and expels the concrete (spalling) while simultaneously keeping the maximum surface temperature lower (around $850^{\circ}C$), thus effectively preventing severe vitrification.

Furthermore, the researchers evaluated the impact of varying the concrete's mix proportions by altering the fine aggregate ratios (40%, 51.4%, and 60%) and increasing the overall paste content. The experimental results demonstrated that these variations had no significant effect on the efficiency, consistency, or cavity depth of the laser scabbling. Detailed microstructural analysis using XRD and FE-SEM confirmed that when vitrification did occasionally occur, it was strictly isolated to the silica-rich areas of the fine aggregate, rather than the limestone coarse aggregate.

In conclusion, the study successfully proves that a 5 kW high-power fiber laser can be safely and effectively used to remove contaminated concrete surfaces from a distance, provided that the concrete retains a sufficient baseline of internal moisture.

Nguyen Phi Long [a], Hiroyuki Daido, Tomonori Yamada, and Akihiko Nishimura, Noboru Hasegawa, Tetsuya Kawachi

Laser Technology Institute, Japan Atomic Energy Agency, 65-20 Kizaki, Tsuruga, Fukui 914-8585, Japan

Naraha Remote Technology Development Center, Japan Atomic Energy Agency, 1-22 Aza-Nakamaru, Oaza-Yamadaoka, Naraha, Futaba, Fukushima 979-0513, Japan

Kansai Photon Science Institute, National Institutes for Quantum and Radiological Science and Technology, 8-1-7 Umemidai, Kizugawa, Kyoto 619-0215, Japan

Journal of Laser Applications IF: 1.8 [Published: 2017]

This study investigates the mechanisms and optimal conditions for drilling and cutting concrete using a high-power quasicontinuous wave (QCW) fiber laser without an assist gas. The study reveals that material removal is primarily driven by vaporization and melt expulsion. When the laser heats the concrete, it creates a molten pool. Recoil pressure from vaporization, combined with the expansion and breakup of trapped gas bubbles, vigorously expels this molten material even after the laser pulse ends.

A key finding is that upward laser irradiation significantly outperforms the conventional downward approach. In upward processing, gravity assists in removing larger molten droplets from the hole, increasing penetration depth by 20% to 30%. Furthermore, the study highlights how varying laser parameters—such as peak power, repetition rate, and overlapping ratio (optimal at 40-50%)—can be tuned to maximize cutting efficiency and prevent clogged kerfs. Notably, the heat-affected zone (HAZ) is kept strictly under 3 mm, demonstrating the QCW laser's high thermal precision for concrete processing.

Yi Jian [a], Xingwang Bai [a*], Penglei Jie [a], Lingfeng Luo [a], Min Mao [a], Changjun Qiu [a], Zebin Zhu [b], Yuguo Kang [b]

[a] School of Mechanical Engineering, University of South China, Hengyang, Hunan, 421001, PR China

[b] Dadi Special Exploration Team of National Mine Emergency Rescue, Bei'jing 100040, China

Optics and Laser Technology IF: 5.0 [Published: 2026]

This study investigates the material removal mechanisms and parameter influences in remote laser cutting of concrete without the use of assisted gas, which is a critical requirement for long-distance rescue and facility demolition. Due to the absence of auxiliary gas to blow away molten slag, the material removal rate in long-distance operations remains relatively low. The research identifies that the primary methods of material removal are splattering, slag dripping, and crack propagation. Splattering is caused by instantaneous vaporization from localized high temperatures, while slag dripping results from gravitational drainage of molten glass through the kerf. Furthermore, crack propagation is induced when internal vapor pressure exceeds the tensile strength of the concrete, leading to structural failure. Experimental results demonstrate that for a 50 mm-thick concrete sample at a distance of 14 m, the cutting speed can reach $1~mm/s$ at 2 kW and $2~mm/s$ at 4 kW. It was found that choosing a positive defocusing (+2 m) configuration significantly enhances performance by enlarging the kerf width and promoting better slag dripping. Additionally, the study proposes a reciprocating cutting method which involves multiple repeated passes; this approach was shown to increase the material removal rate by 11.3% compared to single-pass cutting by re-cutting and ejecting solidified slag deposits. These findings provide a vital parameter basis for improving the efficiency and quality of remote laser cutting in complex emergency and decommissioning scenarios.