Water Absorption Peak Research Articles

Treatment of photoaged neck skin with the pulsed Erbium:YAG laser.

The Erbium (Er):YAG laser represents a new laser approach for the treatment of rhytids and photodamaged skin. Because the Er:YAG laser's 2940-nm wavelength is at the peak of water absorption, this laser produces minimal thermal damage. To document the Er:YAG laser's efficacy in the treatment of neck rhytids. Ten patients with neck rhytids were treated with the Er:YAG laser. All individuals were evaluated for clinical improvement, scarring, and pigmentary changes. All patients showed fair to excellent results with no scarring or pigmentary changes at 6 months. The Er:YAG laser may be used to improve nonfacial photodamaged skin.

Laser ablation as a function of the primary absorber in dentin.

Infrared transmission spectra of dentin reveal a broad absorption band between 6.0 and 7.0 microns composed of absorption peaks of water, collagen and carbonated hydroxyapatite. The nearly constant absorption and the existence of absorption peaks of different tissue components were used to investigate ablation as a function of the primary absorber. Laser ablation of dentin as a function of fluence was studied in the wavelength range between 6.0 and 7.5 microns using the Vanderbilt Free-Electron Laser (FEL). Depth and volume of the ablation crater were determined with a silicon replica method and subsequent confocal laser topometry. SEM investigations were performed on the irradiated surfaces. For the description of the experimental data an ablation model is developed. At all applied wavelengths we found a linear increase of ablation depth as a function of fluence above a threshold fluence. The lower absorption of dentin at 7.5 microns compared to the absorption at 6.0, 6.5 and 7.0 microns results in a greater ablation threshold. At 6.0, 6.5 and 7.0 microns wavelengths the ablation thresholds are comparable. The experimental data are in good agreement with an ablation model using a mean absorption coefficient of the target material. No thermal cracking is observed after ablation in dentin. The post ablative surface structure at 6.0 and 7.0 microns looks similar whereas at 7.5 microns the surface reveals a greater roughness. The ablation efficiency and threshold depend on the mean absorption but do not depend upon the chemical identity of the primary absorber in dentin. Calculations show that heat conduction during the laser pulse leads to a thermal equalization between the heated microstructures and surrounding tissue resulting in an ablation with little dependence on the primary absorber.

Chemical Durability and Infrared Transmission in the YF3-PbF2-CdF2-AIF3Glasses

Glass formation region, thermal stability and chemical durability have been determined in the four component glassy YF3-PbFrCdF2-AIF3 (YPCA) system. The notable features of these glasses are thermal stability at 110°C, IR transmission of ∼ 80% with long wavelength cut-off at 9.5 μm and excellent chemical stability. These features are superior to zirconium fluoride glasses conventionally used as infrared materials. An important characteristic of the glass, i.e. water durability has been studied using three different techniques, namely static dissolution test, monitoring water absorption peak in the IR spectrum with dipping time and by analysis of the leached solution. The results from all the three methods complement each other and the glasses show excellent resistance to water attack at ambient temperature. YPCA glasses, therefore, appear as promising candidates for infrared related applications.

Temperature dependence of the absorption coefficient of water for midinfrared laser radiation.

The dynamics of the water absorption peak around 1.94 microns was examined. This peak is important for the absorption of holmium and thulium laser radiation. To examine the effect of temperature on the absorption coefficient, the transmission of pulsed Ho:YAG, Ho:YAG, Ho:YSGG, and Tm:YAG laser radiation through water of 22 degrees C, 49 degrees C, and 70 degrees C was measured as a function of the thickness of the water layer. From these data the absorption coefficients were determined at the three wavelengths. We found that at all three wavelengths, the absorption coefficients decreased when increasing the temperature. Second, the absorption spectrum of water was measured from 1,850-2,150 nm with a spectrophotometer. It was found that the absorption peak at 1.94 microns (at 22 degrees C) shifts to shorter wavelengths with increasing temperatures, to 1.92 microns at 70 degrees C. A model was developed to predict the temperature distribution incorporating the dynamic change in absorption coefficient. The temperature distributions are compared to the predictions of a model assuming constant optical properties. It is shown in this study that the dynamics of the absorption coefficient has a significant influence on the expected zone of damage and ablation parameters in the 2-microns wavelength range.

Laser microsclerostomy for primary open angle glaucoma: a review of laser mechanisms and delivery systems.

A number of different lasers and delivery systems are currently used in experimental sclerostomy procedures. These are discussed with reference to their performance in terms of cutting accuracy and trauma to the adjacent tissues. Lasers emitting wavelengths close to the absorption peaks of water in the mid-infrared region and organic polymers in the far ultraviolet region have a short absorption pathlength in the sclera and produce the least adjacent thermal tissue trauma. These ablating lasers cannot be delivered gonioscopically, and contact endoscopic techniques trap hot expanding gases within the forming sclerostomy channel causing secondary thermal and mechanical damage. Optimal results should be obtained using an ablating laser delivered either through an open mask or a modified endoscopic system incorporating an adequate exhaust mechanism.

A fiberoptic compatable midinfrared laser with CO 2 laser-like effect: Application to atherosclerosis

In theory, pulses of laser light in the 2-μm range should ablate tissue in a manner similar to that of the 10.6-μm CO 2 laser with the added advantage of efficient transmission through flexible quartz fibers. Using 200-μsec pulses of 2.15-μm thulium—holmium—chromium:YAG (THC:YAG) laser light, we were able to create 700-μm-diameter holes through calcific atherosclerosis in vitro. In vivo evaluation of thrombogenicity and healing was accomplished by exposing the luminal surface of rabbit aortas to the THC:YAG laser. Serial histologic examinations of laser-treated rabbit aortae revealed a time course of resolution of the lesions which was very similar to that observed with like-sized lesions created with the same amount of continuous wave CO 2 energy. No significant differences in thrombogenicity nor healing response were noted. The excellent in vivo response observed is due in part to the pulsed nature of the THC:YAG laser output as well as to the efficient tissue absorption at the 2.15-μm wavelength. We feel that excellent ablative effects with minimal collateral thermal damage can be obtained through fiberoptic delivery systems by taking advantage of laser wavelengths corresponding to the infrared absorption peak of water in the 2-μm region and pulsed delivery of the laser energy.

New long-wavelength Nd:YAG laser at 1.44 micron: effect on brain.

A wavelength-shifted Nd:YAG laser, tuned to coincide with the infrared absorption peak of water at 1.44 microns, was used to make lesions in normal rabbit brain. A total of 48 lesions were made with power up to 20 W, with energy up to 40 joules, and with two different spot sizes. These lesions were compared to lesions made with 1.06 microns radiation from an Nd:YAG laser under identical operating conditions. Measurements of blood-brain barrier damage and width, depth, and volume of tissue affected were obtained 30 minutes after placement of the lesions. It was found that 1.44-microns lesions produced photoevaporative tissue loss at the highest intensities used. The layer of coagulated tissue remaining after photovaporization had a mean thickness of 0.6 mm irrespective of the volume of tissue removed. There was no photovaporization in the 1.06-microns lesions. In addition, the amount of peripheral edema per unit volume of tissue coagulated was approximately half at the 1.44-microns wavelength. These findings suggest that the 1.44-microns Nd:YAG laser may be a useful surgical instrument since it combines the photoevaporative effect of the CO2 laser while maintaining the advantages of the conventional Nd:YAG laser (quartz fiber delivery and effective hemostasis).

An extension of the three-zone model to predict depth of tissue damage beneath Er:YAG and Ho:YAG laser excisions

Pulsed lasers such as Er:YAG and Ho:YAG with outputs at mid-infrared wavelengths emit radiation which may be transmitted by fibre to a treatment site. The thickness of soft-tissue damage beneath excisions made by these lasers is predicted using an extension to a model previously devised for CO2 laser radiation. The minimum achievable thickness occurs at a water absorption peak and at such high irradiance that heat cannot diffuse significantly compared with the radiation penetration depth. This minimum thickness is estimated to be in the order of 10 mu m for the Er:YAG laser.

Preliminary Report on Corneal Incisions Created by a Hydrogen Fluoride Laser

We created corneal incisions in eye bank eyes with a pulsed hydrogen fluoride infrared laser. This laser was selected because its emission spectrum (2.7 to 3.0 micron) closely corresponds to the absorption peak of water in the infrared region. Short pulses (200 nsec) of hydrogen fluoride laser light focused with a cylindrical lens resulting in radiant exposures of 1.3 J/cm2 at the corneal surface created linear cuts in the cornea with minimal thermal damage adjacent to the incision, suggesting that the pulsed hydrogen fluoride laser may be useful for corneal surgery.

A Nuclear Magnetic Resonance Study of Water in Cold-acclimating Cereals

Continuous wave nuclear magnetic resonance (NMR) studies indicated that the line width of the water absorption peak (Deltav(1/2)) from crowns of winter and spring wheat (Triticum aestivum L.) increased during cold acclimation. There was a negative correlation between Deltav(1/2) and crown water content, and both of these parameters were correlated with the lowest survival temperature at which 50% or more of the crowns were not killed by freezing (LT(50)). Regression analyses indicated that Deltav(1/2) and water content account for similar variability in LT(50). Slow dehydration of unacclimated winter wheat crowns by artificial means resulted in similarly correlated changes in water content and Deltav(1/2). Rapid dehydration of unacclimated crowns reduced water content but did not influence Deltav(1/2). The incubation of unacclimated winter wheat crowns in a sucrose medium reduced water content and increased Deltav(1/2). The increase in Deltav(1/2) appears to be dependent in part on a reduction in water content and an increase in solutes.Longitudinal (T(1)) and transverse (T(2)) relaxation times of water protons in cereals at different stages of cold acclimation were measured using pulse NMR methods. The T(1) and T(2) signals each demonstrated the existence of two populations of water, one with a short and one with a long relaxation time. During the first 3 weeks of acclimation, the long T(2) decreased significantly in winter-hardy cereals, and did not change in a spring wheat until the 5th week of hardening. There was no change in the long T(1) until the 3rd week of hardening for the winter cereals and until the 7th week of hardening for the spring wheat. No simple relationship could be established between T(1) or T(2) and cold hardiness. Neither continuous wave or pulsed NMR spectroscopy can be used as a diagnostic tool in predicting the cold hardiness of winter wheats. An increase in Deltav(1/2) or a reduction in relaxation times does not provide evidence for ordering of the bulk of the cell water.

Liquid water in frozen tissue: study by nuclear magnetic resonance.

Nuclear magnetic resonance (NMR) spectroscopy was used to examine the behavior and extent of liquid water in postrigor-frozen tissue of cod at temperatures below 0 degrees C. A liquid-water phase persists in the tissue down to about -70 degrees C; the extent of the phase decreases rapidly between 0 degrees and -10 degrees C and slowly at lower temperatures. That the NMR absorption peak of the liquid water increases in width, with decreasing temperature, suggests loss of mobility or structuring of the phase. A technique for introducing geometrically uniform cores of muscle into the probe of the high-resolution spectrometer permits quantitative determinations of liquid water.

Ultra-Violet Absorption Spectrum of Water

ON further examination, the absorption peaks of water recently discussed1 have been found to be inherent in the instrumental technique used. The fall in the values of optical density at the lower wavelengths is the normal stray-light effect under these conditions, but the ‘fine structure’ is now thought to be due to the oxygen absorption in the factory-sealed monochromator and inadequate compensation within the instrument when the slit automatically opens and closes on passing through the wave-lengths at the oxygen absorption peaks.

Ultra-Violet Spectra of Water Solutions

RECENTLY, investigations of the ultra-violet absorption spectra of inorganic and organic ions in the wave-length range below 250 mµ have been made. At the shortest wave-lengths obtainable on the commercial instruments some interesting results were obtained. These show that the absorbances measured were not primarily due to the ions under examination, but resulted from a series of water absorption peaks which are strongly enhanced by the presence of solutes. The spectra were measured on a Beckman DK2 using 1-cm. silica cells, and one sample was reproduced on a ‘Uvispek’ with silica optics.