?In of having damage threshold higher than 1?m lasers

?In this paper, we have done a comparative study of the eye-safe nature of the rare-earth-doped fiber lasers at different powers in continuous wave regime. The erbium lasers operating at eye-safe region are no longer safe at higher power due to parasitic lasing. The Raman fiber lasers at 1.5?m are proved to be power scalable laser in the eye-safe region. We have demonstrated that the eye-safe nature of these lasers increases with increasing power. The safety of these lasers is even comparable to Erbium lasers at high power.Over the past two decades, the power scaling of fiber lasers has increased remarkably in the continuous wave regime 1,2. The scalability is achieved because of their compactness, robustness of architecture, high gain and high stability. These lasers provide wide tunability, higher efficiency and good beam quality over the entire operating power range. So, they have huge applications in medicine, defence, communication, spectroscopy, metrology, industries etc. The fiber lasers used in medicine and healthcare are usually doped with ytterbium, thulium, erbium, and holmium 3.

The commercially available continuous wave (CW) ytterbium-doped fiber laser has a record power of a multi-moded output of 100s of kWs 2 and near diffraction limited output of 20 kW  2. Their emission window is 1050-1120 nm, which is unsafe for eyes and can cause permanent damage to the retina 4. Erbium lasers at 1550 nm are called as eye-safe lasers because of having damage threshold higher than 1?m lasers 4. These lasers have accomplished the maximum single-mode output power of 103W 5,6and 405W 7 as multi-moded output. Thulium fiber lasers operating near water absorption peak (1.94?m) have been used in soft biological tissue incision 3.They have achieved a single-mode record power of 1kW 8. These lasers are safe for the retina but can harm cornea or lens 4. The limited powers in the eye-safe region have given rise to the development of the Raman fiber lasers 9.

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Due to the immense impact of these high power fiber lasers in various fields, their safety is a concern. The maximum permissible exposure (MPE) limits for the safe use of these lasers  are recommended by the international standards like ANSI Z136.1 and IEC 60825-1 10,11.

In this paper, we have assessed the eye safety of different continuous wave fiber lasers.