An Nd:YAG laser with a water-guided laser beam--a new transmission system

Experimental Study on Carbon Fiber-Reinforced Polymer Groove Machining by High-Power Water-Jet-Guided Laser

Due to the excellent properties of carbon fiber-reinforced polymers (CFRPs), such as high strength and strong corrosion resistance, the traditional water-jet-guided laser (WJGL) technology has problems with fiber pull-out and has a small cutting depth when processing CFRPs. Therefore, in this study, we used high-power water-jet-guided laser (HPWJGL) technology to perform groove processing experiments on CFRPs. The effects of four key process parameters, high laser power, pulse frequency, feed rate, and water-jet pressure, on the cutting depth were investigated by a single-factor experiment. The formation mechanism of groove cross-section morphology and the processing advantages of high-power water-jet-guided lasers were analyzed. On this basis, the mathematical prediction model of cutting depth was established by using the response surface method (RSM), and the optimal combination of process parameters was obtained. The mathematical prediction model was verified by experiments, and the error was only 1.84%, indicating that the model had a high reference value. This study provides a reference for the precision machining of HPWJGL technology.

Light-guiding effect in a two-fluid model of laser angioplasty

Mixing and optical characteristics of blood and optical fluid, utilized in laser angioplasty, are investigated with a two-fluid model. Transport equations are solved for the zone-averaged variables of each fluid with allowance for momentum transport at the interface. The predicted volume fractions of the fluids are used as weight functions to calculate the mixture refractive index. A set of light rays are traced through the fluids to the plaque, utilizing the mixture refractive index. The results indicate significant effect of flow characteristics on the focusing of the rays.

A model of blood interaction with optical-fluid guide for laser angioplasty

A mathematical model is developed to describe the flow and mixing of blood and optical fluid used in liquid-guided light for laser angioplasty. The model is based on a two-fluid formulation in which separate transport equations are solved for the blood and the optical fluid. Empirical relations, established in prior work, are used to represent interfluid transport of momentum. Both steady and phasic inflow conditions are considered. Parametric calculations are performed showing effect of relative flow rates of blood and optical fluid, on the mixing phenomena. The relative velocity considered (based on average blood velocity) ranged from 0.08 to 0.28 m/sec. No allowance has been made for ablation of the plaque. The predicted results include spatial distribution of the velocity field and the existence probabilities (volume fractions) that provide a measure of the extent of mixing between the fluids. It is found that the degree of mixing is adversely affected by the relative inflow velocity between blood and optical fluid and the pulsatility of blood inflow. Deep penetration of the optical fluid is predicted at high relative velocity and at the end of diastolic and early systolic stages of the cardiac cycle.

Water-jet-cooled Nd:YAG laser coagulation of experimental liver metastases: correlation between ultrasonography and histology

To establish the value of ultrasonography in imaging laser coagulation of tumor and surrounding tissue, the relation between measurements on ultrasound and histology was determined in a rat tumor model. A piece of colon carcinoma CC531 was implanted in the liver of 21 Wag/Rij rats; 20 days later, tumors (mean diameter 5.3 mm) were treated with a water-jet-cooled Nd:YAG laser at 10 W and either 150 J, 300 J, 600 J, 1,200 J, 1,700 J, or 2,400 J. Ultrasonography was done just pre- and immediately post-laser treatment. The animals were sacrificed and livers removed for light microscopical evaluation. Depth and width of coagulation were measured directly on ultrasound, and on histological samples by computer-assisted image analysis. Laser treatment did not change the echogenic aspect of the tumor on ultrasound. However, liver damage appeared hypoechoic compared to normal liver. A significant correlation was found between the total size of the lesion on ultrasound and histology (P = 0.015, r = 0.57 for depth; P = 0.012, r = 0.58 for width), suggesting that laser induced tumor destruction may be derived from the amount of surrounding hepatic damage on ultrasound.

Water-jet-cooled Nd:YAG laser coagulation: selective destruction of rat liver metastases

The photocoagulating properties of the water-jet-cooled Nd:YAG laser (1,064 nm) have been studied in a rat tumor model. A colon carcinoma CC531 was implanted in the liver; 20 days after inoculation, laser therapy was performed with 600 J, 850 J, 1,200 J, 1,700 J, or 2,400 J at a power setting of either 10 or 20 W. Liver damage was determined in tissue specimen on day 1 after treatment and by serum levels of alanine aminotransferase and aspartate aminotransferase on day 1 and 2. Tissue specimen of day 36 were used to evaluate tumor remission. Liver function was assessed by antipyrine clearance on day 2. Light microscopic examination on day 1 showed coagulative necrosis up to 10 mm in diameter at 1,700 J and 20 W. At 20 W, liver damage was 22% larger than at 10 W (P = 0.0001). A significant relationship was found between laser energy and liver damage with complete tumor destruction in all animals at 2,400 J. No deterioration in liver function was found. The results of this study show the ability of the water-jet-cooled Nd:YAG laser to produce tumor coagulation necrosis with minor liver damage.

Gastrointestinal laser endoscopy--future horizons

The laser, especially the neodymium:yttrium-aluminum-garnet device, has been a dominant influence on the development of gastrointestinal therapeutic endoscopy. More than 2,000 such procedures were performed in the first 5 years of experience with laser endoscopy at the Mayo Clinic. The major areas for future development are (1) the control of acute and chronic gastrointestinal bleeding, (2) the palliation of malignant gastrointestinal neoplasms, and (3) the management of benign and malignant obstructive lesions of the biliary tract. Refinements in laser devices, delivery systems, and techniques such as photodynamic therapy will be needed to achieve more selective tissue destruction. Improvements in the new adjunctive endoscopic methods of electronic (video) endoscopy and ultrasonography may enhance evolving laser applications by more accurately identifying diseased tissues and guiding their destruction.