Eye Safety and Nonlethal Lasers

An evaluation of Ocular Hazards and Safety Standards

By Dr. Scott C. Buchter, Ph.D (Lasersec Systems Corporation)

INTRODUCTION

Nonlethal lasers are beginning to emerge in the market as the strategy of choice for various applications ranging from crowd control, coast/border control, anti-piracy operations, avian dispersal, sniper detection and more uses that are still under development. The range and effectiveness of lasers is unmatched by any other nonlethal technology. After many years of successful deployment in military settings non-lethal lasers are now expanding into the commercial sector. With this expansion comes new safety challenges. Understanding existing eye safety standards, as well as the factors in the environment that impact eye safety is essential.

Equipment manufacturers, laser safety professionals, and security service providers are working together to build safe and reliable systems that deliver the next generation of nonlethal laser protection. This white paper presents a review of laser ocular hazards, safety standards, and eye-safe operation of non-lethal laser devices. Additionally, the paper highlights considerations when evaluating the eye-safety of nonlethal laser systems, and uses the Lasersec Systems SeaLase® and Medusa® lasers as examples of compliant systems.

Lasers and the Eye

The human eye is a sophisticated and sensitive optical detector with a peak visual response to light in the visual range (~550 nm) that has evolved over time to correspond to the peak of the solar spectrum. Like any other living tissue, the tissues of the eye are susceptible to damage under extreme conditions. Since different tissues absorb some wavelengths more strongly than others, different parts of the eye are variably susceptible to damage at a given wavelength. The cornea, the lens, and the retina are all in the path of light entering the eye and therefore may be subjected to dangerous light levels.

Many factors combine to result in the potential for laser-induced ocular injury. The anatomy of the eye, physiology of vision, and laser-tissue interaction are key factors that need to be assessed. Laser-tissue interaction is strongly dependent on wavelength, power, and pulse duration. Damage can occur by several mechanisms including photochemical, thermal, and thermo-acoustic.

Photochemical interactions are those in which an absorption of a photon by a molecule results in a chemical reaction.

Thermal interactions refer to the deposition of heat to a local area.

Thermo-acoustic refers to transient phenomena where the rapid deposition of heat results in a damaging shock-wave.

In terms relative to the human eye, a thermal interaction might result in a slow burn at the irradiated site, whereas the thermo-acoustic interaction could cause additional physical damage beyond the burn site.

As described, specific tissues in the eye interact strongly with different portions of the optical spectrum. The cornea and lens are transparent to the visible wavelengths at which non-lethal laser systems operate. As such, the potential hazards deal mainly with retinal damage.

Laser Safety Standards

The eye safety hazards of lasers were recognized within a year of the first demonstration of a laser device. As some of the first adopters of laser technology and research, military agencies issued the earliest laser safety guidelines. In the 1960s and ‘70s, biomedical research regarding laser-tissue interactions established the first physiological basis for safe exposure limits. In over 40 years of research and development, the variety of lasers now spans the spectrum from the vacuum ultraviolet to the far-infrared, with pulsewidths as short as femtoseconds (10-15 s).

The task of providing laser safety guidelines and regulatory codes that adequately address such a broad field of devices and diverse applications has become significant. The capabilities of laser systems have advanced and the complexity of safety standards have kept pace.

There are a number of regulatory, governmental, and educational organizations that have developed and published laser safety standards, three of which are discussed in the following paragraphs. The standards generally have the following main functions:

Some standards are for manufacturers of laser systems providing regulatory codes on how laser products can be made, classified, and labeled, for example. Other standards are considered user standards and address how individuals and organizations should deploy and safely use laser systems

Lasers and the Eye

The human eye is a sophisticated and sensitive optical detector with a peak visual response to light in the visual range (~550 nm) that has evolved over time to correspond to the peak of the solar spectrum. Like any other living tissue, the tissues of the eye are susceptible to damage under extreme conditions. Since different tissues absorb some wavelengths more strongly than others, different parts of the eye are variably susceptible to damage at a given wavelength. The cornea, the lens, and the retina are all in the path of light entering the eye and therefore may be subjected to dangerous light levels.

Many factors combine to result in the potential for laser-induced ocular injury. The anatomy of the eye, physiology of vision, and laser-tissue interaction are key factors that need to be assessed. Laser-tissue interaction is strongly dependent on wavelength, power, and pulse duration. Damage can occur by several mechanisms including photochemical, thermal, and thermo-acoustic.

Photochemical interactions are those in which an absorption of a photon by a molecule results in a chemical reaction.

Thermal interactions refer to the deposition of heat to a local area.

Thermo-acoustic refers to transient phenomena where the rapid deposition of heat results in a damaging shock-wave.

In terms relative to the human eye, a thermal interaction might result in a slow burn at the irradiated site, whereas the thermo-acoustic interaction could cause additional physical damage beyond the burn site.

As described, specific tissues in the eye interact strongly with different portions of the optical spectrum. The cornea and lens are transparent to the visible wavelengths at which non-lethal laser systems operate. As such, the potential hazards deal mainly with retinal damage.