There is an increasing use of near-infrared lasers in biomedical applications operating in the spectrum between 1300 and 1400 nm. To corroborate and expand the existing safety data for skin exposure to lasers in this wavelength region, the in-vivo ED50 damage thresholds were determined in Guizhou miniature pigs for 1319-nm laser radiation. Exposure durations of 0.4, 1.0, and 3.0 s and 1 / e2 beam diameters of 0.98 and 1.96 cm were employed. Damage lesion determinations were performed at 1- and 24 h post exposure. The Bliss probit analysis was employed to establish the ED50 damage thresholds. Histopathological studies of skin damage were performed at 48 h after irradiation to reveal the damage characteristics. The skin damage thresholds at 1 h post exposure, given in peak radiant exposure, were 35.5, 36.1, and 37.1 J / cm2 at exposure durations of 0.4, 1.0, and 3.0 s with the spot diameter of 0.98 cm, and 28.6 J / cm2 at exposure duration of 3.0 s with the spot diameter of 1.96 cm. At 24 h post exposure, the ED50s increased slightly. Histologically, the thermal damage characteristics at the near-threshold level included gathering of the nuclear chromatin and cell vacuolation in the epidermis and deposition of blood cells in the capillary vessels. However, at the apparently above-threshold level, the damage characteristics included obvious stretching of the nuclear chromatin in the epidermis, closing of the capillary lumen, structural change of collagen fibers, and coagulative necrosis of the hair follicle cells. The damage induced by this laser could go deep into the fatty tissue. The obtained results may contribute to the knowledge base for the damage mechanisms and expand the database for the refinement of laser safety standards in the wavelength range of 1300 to 1400 nm.
The corneal damage effects induced by 1319-nm transitional near-infrared laser have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. The in vivo corneal damage thresholds (ED50s) were determined in New Zealand rabbits for 1319-nm laser radiation for exposure durations from 75 ms to 10 s. An additional corneal ED50 was determined at 1338 nm for a 5-ms exposure. The incident corneal irradiance diameter was fixed at 2 mm for all exposure conditions to avoid the influence of spot size on threshold. The ED50s given in terms of the corneal radiant exposure for exposure durations of 5 ms, 75 ms, 0.35 s, 2 s, and 10 s were 39.4, 51.5, 87.2, 156.3, and 311.1 J/cm2, respectively. The 39.4 J/cm2 was derived from the ED50 for 1338 nm (27.0 J/cm2). The ED50s for exposure durations of 75 ms to 10 s were correlated by a power law equation, ED50=128.9t0.36 in J/cm2, where t was the input in the unit of second, with correlation coefficient (R) of 0.997. Enough safe margins existed between the ED50s and the maximum permitted exposures from current laser safety standard.
Supercontinuum (SC) source is a new kind of artificial light source, having the characteristics of both laser and traditional incoherent light source, i.e., high brightness, good direction, and super broadband spectrum. The rapid development of SC source stimulates our concern on its ocular damage potency. However, the damage effects of SC source have never been explored. The retinal damage threshold of chinchilla grey rabbit induced by a Vis-infrared SC source was determined for the first time. Additionally, a theoretical method was also developed for analyzing the hazard risks of SC source.
With the widespread use of high-power laser systems operating within the wavelength region of approximately 1.3 to 1.4 μm, it becomes very necessary to refine the laser safety guidelines setting the exposure limits for the eye and skin. In this paper, an optical-thermal-damage model was developed to simulate laser propagation, energy deposition, heat transfer and thermal damage in the skin for 1.319 μm laser irradiation. Meanwhile, an experiment was also conducted in vitro to measure the tempreture history of a porcine skin specimen irradiated by a 1.319 μm laser. Predictions from the model included light distribution in the skin, temperature response and thermal damge level of the tissue. It was shown that the light distribution region was much larger than that of the incident laser at the wavelength of 1.319 μm, and the maximum value of the fluence rate located on the interior region of the skin, not on the surface. By comparing the calculated temperature curve with the experimentally recorded temperautre data, good agreement was shown betweeen them, which validated the numerical model. The model also indicated that the damage integral changed little when the temperature of skin tissue was lower than about 55 °C, after that, the integral increased rapidly and denatunation of the tissue would occur. Based on this model, we can further explore the damage mechanisms and trends for the skin and eye within the wavelength region of 1.3 μm to 1.4 μm, incorporating with in vivo experimental investigations.
The near infrared laser technique can activate cutaneous nociceptors with high specificity and reproducibility and be
used in anti-riot equipment. This study aimed to explore cutaneous pain effect and determine the threshold induced by
Nd:YAG and CO2 laser stimuli. The corresponding wavelength was 1.32μm and 10.6μm. The pain effect was assessed in
three healthy subjects (1 woman and 2 men) on the skin of dorsum of both hands. The energy of each pulse and whether
the subjects felt a painful sensation after each stimulus were recorded. A simplified Bliss Method was used to calculate
the pain threshold which were determined under three pulse durations for Nd:YAG laser and one pulse duration for CO2
laser. As a result the pain thresholds were determined to be 5.6J/cm2, 5.4J/cm2 and 5.0J/cm2 respectively when using
Nd:YAG laser, 4.0mm beam diameter, 8ms, 0.1s and 1s pulse duration. The pain threshold was 1.0J/cm2 when using CO2
laser, 4.0mm beam diameter and 0.1s pulse duration. We concluded that the threshold of cutaneous pain elicited by
1.32μm laser was independent upon the pulse duration when the exposure time ranged from 8ms to 1s. Under the same
exposure condition, the threshold of cutaneous pain elicited by 1.32μm laser was higher than that elicited by 10.6μm
The flash electroretinography is a standard electrophysiological method and widely employed in basic research and
ophthalmology clinics, of which the stimulus is usually white flash from dome stimulator. However, little is known about
the electroretinograms (ERGs) evoked by monochromatic laser flash stimuli. The goal of this research effort is to
quantify the ERGs of dark-adapted New Zealand rabbits elicited by He-Ne laser flash with wavelength 632.8 nm. The
flash field was a Maxwellian viewing disc with angular subtense of 8.5°, 13.3° or 20.2°. The stimulus duration was 12
ms, 22 ms, 70 ms or 220 ms. The laser flash power incident on the cornea varied from 2.2 nW through 22 mW. Under the
condition of 20 ms stimulus duration and 20.2° flash field, the ERG of New Zealand rabbit was compared with that of
Chinchilla gray rabbit. Results showed that for the ERG b-wave, with the increase of laser energy, the amplitude first
increased, then met a trough and finally increased again, the implicit time decreased first and then met a platform. While
for the ERG a-wave, the amplitude increased and the implicit time decreased monotonically. Longer stimulus duration
led to lower b-wave amplitude under equal flash power level. The flash field size showed limited effect on the ERG,
especially on the low energy end. As compared with the pigmented rabbit, the albino rabbit was more sensitive and the
threshold energy for b-wave excitation was about 10 times lower.
The laser-tissue interaction has not been well defined at the 1319 nm wavelength for brain exposure. The goal of this
research effort was to identify the behavioral and histological changes of brain lesion induced by 1319 nm laser. The
experiment was performed on China Kunming mice. Unilateral brain lesions were created with a continuous-wave
Nd:YAG laser (1319nm). The brain lesions were identified through behavioral observation and histological haematoxylin
and eosin (H&E) staining method. The behavior change was observed for a radiant exposure range of 97~773 J/cm2. The
histology of the recovery process was identified for radiant exposure of 580 J/cm2. Subjects were sacrificed 1 hour, 1
week, 2 weeks, 3 months, 7 months and 13 months after laser irradiation. Results showed that after laser exposure,
behavioral deficits, including kyphosis, tail entasia, or whole body paralysis could be noted right after the animals
recovered from anesthesia while gradually disappeared within several days and never recurred again. Histologically, the
laser lesion showed a typical architecture dependent on the interval following laser treatment. The central zone of
coagulation necrosis is not apparent right after exposure but becomes obvious within several days. The nerotic tissue
though may persist for a long time, will finally be completely resorbed. No carbonization granules formed under our
To study 1.06μm laser causing pain in human skin. The skin of human dorsum hand was irradiated by a Nd: YAG laser.
The energy of each pulse and whether the subjects felt a painful sensation after each stimulus were recorded. The pain
threshold was defined as the laser dose at which the subjects reported a painful sensation to 50% of stimulus deliveries.
The pain thresholds were determined under 3 different beam diameter and pulse duration conditions. The influence of
skin temperature on the pain caused by laser stimulus was also explored. As the temperature of skin was about 30°C, the
pain thresholds were 394mJ/mm2, 36.4mJ/mm2 and 8.92mJ/mm2 respectively under the stimulating condition of 1.20mm
beam diameter and 85μs pulse duration, 1.20mm beam diameter and 20ns pulse duration and 2.56mm beam diameter and
20ns pulse duration. Under the first condition, when skin temperature was 25°C and radiant exposure was 383mJ/mm2,
the probability of laser stimulus causing pain was 16.7%; when skin temperature was 39°C and radiant exposure was
361mJ/mm2, the probability was 56.7%. The threshold of 1.06μm laser stimulus causing pain decreases with decreasing
pulse duration, increasing beam diameter and skin temperature.