Dale J. Payne

Ultrashort laser pulse bioeffects and safety

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than 1 ns than that for longer pulses. It has also been shown that more energy is required for near-infrared (NIR) wavelengths than in the visible because the light focuses behind the retina, requiring more energy to produce a damaging fluence on the retina. We review the progress made in determining the trends in retinal damage from laser pulses of 1 ns to 100 fs in the visible and NIR wavelength regimes. We have determined the most likely damage mechanism(s) operative in this pulse width regime.

Cavitation thresholds in the rabbit retinal pigmented epithelium

We performed measurements to examine retinal injury from laser pulses in the sub-nanosecond time regime. Both ex-vivo porcine and Dutch belted rabbit retinal pigment epithelium (RPE) models were used in conjunction with time resolved imaging to observe cavitation bubble formation. Included in this study are 3 ps, 300 fs, and 100 fs pulses at a wavelength of 580 nm, as well as 70 ps and 5 ns pulses at 532 nm. Threshold values varied between 37 mJ/cm2 and 50 mJ/cm2 across the range of pulse widths. Following laser irradiation cell viability was checked using a fluorescent dye marker (calcein). Our current results are compared to an earlier investigation using the artificial retina model.

Retinal damage mechanisms and safety for ultrashort laser exposure

For the past several years the US Air Force has led a research effort to investigate the thresholds and mechanisms for retinal damage from ultrashort laser pulses [i.e. nanosecond (10-9 sec) to femtosecond (10-15 sec) pulse widths]. The goal was to expand the biological database into the ultrashort pulse regime and thus to allow establishment of maximum permissible exposure limits for these lasers. We review the progress made in determining trends in retial damage by ultrashort laser pulses in the visible and near infrared, including variations in spot size and number of pulses. We also discuss the most likely damage mechanisms operative in this pulse width regime and discuss relevance to laser safety.

Visible lesion threshold dependency on Retinal spot size for ultrashort laser pulses in the near infrared

Single pulses in the near-infrared (1060 nanometers) were used to measure retinal spot size dependence of minimum visible lesion (MVL) thresholds in rhesus monkey eyes at a pulsewidth of 150 femtoseconds. We report the MVL thresholds determined at 1 hour and 24 hours post exposure which were obtained with 2 different lenses placed in front of the eye to vary the retinal spot size. Also we report the fluorescein angiography thresholds (FAVL) for the above measurements. These new data points will be added to the databank for Retinal Maximum Permissible Exposure (MPE) as a function of spot size for this pulsewidth and a comparison will be made with previous spot size dependency studies. Our measurements show that the retinal ED50 threshold fluence decreases for increasing retinal spot sizes. The fluence at the MVL threshold decreased by a factor of 3 for an increase in retinal image diameter by a factor of 4.5 times from the smallest to largest spot size.

White-light interferometric measurements of aqueous media dispersive properties

We present dispersion curves for aqueous media measured with a white-light interferometric technique. Data is presented for wavelength ranges in the visible and near IR. Materials investigated include high purity water and primate vitreous. Results are examined with regard to retinal damage mechanisms associated with ultrashort laser pulse exposures. In this pulse duration regime the dispersive nature of the medium can play a critical role in predicting damage thresholds. These values are also critical to the development of nonlinear propagation models. We compare our results to other measurement techniques which determined index of refraction at a series of single wavelength points. Results indicate that he dispersive trends in the materials can be quickly and accurately mapped over a wide spectral range using this technique.

Threshold energies in the artificial retina

Laser threshold energies for artificial retinal damage from ultrashort (i.e. less than or equal to 1 ns) laser pulses are investigated as a function of both pulse width and spot size. A piece of film acts as the absorbing layer and is positioned at the focus of the Cain artificial eye (17 mm in water). We performed experiments at the focal point, and at two and ten Rayleigh ranges in front of the focus with the damage endpoint being the presence of a bubble coming off the film. Thresholds were determined for wavelengths of 1064 nm, 580 nm, and 532 nm with pulse durations ranging from the nanosecond (ns) to the femtosecond (fs) regimes. For the at-focus data in the visible regime, the threshold dropped from 0.25 (mu) J for a 5 ns pulse at 532 nm to 0.11 (mu) J for a 100 fs, 580 nm pulse. Similarly, for the near infrared (NIR) the threshold changed from 5.5 (mu) J for a 5 ns pulse to 0.9 (mu) J for a 130 fs pulse. These results are discussed in the context of applicable nonlinear optical phenomena.

Ultrashort-laser-pulse retinal damage

Recent studies of retinal damage due to ultrashort laser pulses have shown that less energy is required for retinal damage for pulses shorter than one nanosecond. Laser minimum visible lesion thresholds for retinal damage from ultrashort laser pulses are produced at lower energies than in the nanosecond to microsecond laser pulse regime. We review the progress made in determining the trends in retinal damage from laser pulses of one nanosecond to one hundred femtoseconds in the visible and near-infrared wavelength regimes. We have determined the most likely damage mechanism operative in this pulse width regime and discuss implications on laser safety standards.

Retinal damage mechanisms from ultrashort laser exposure

Extensive research of ultrashort ocular damage mechanisms has shown that less energy is required for retinal damage for pulses shorter than one nanosecond. Laser minimum visible lesion thresholds for retinal damage from ultrashort (i.e. < 1 ns) laser pulses occur at lower energies than in the nanosecond to microsecond laser pulse regime. WE review the progress made in determining the trends in retinal damage from laser pulses of one nanosecond to one hundred femtoseconds in the visible and near-infrared wavelength regimes. We discuss the most likely damage mechanism(s) operative in this pulse width regime and discuss implications on laser safety standards.