A coherent fiber laser array in a Self-Fourier cavity is described. The Self-Fourier cavity has been shown to coherently
combine an array of fiber lasers through its ideal supermode discrimination as a result of its passive coupling matrix of
rank 1. Recently, a static model has been developed that extrapolates this technique to an array of very large number of
fiber lasers by exploiting the gain-dependent phase shift and incorporating specific levels of individual feedback to each
fiber amplifiers, transforming them into regenerative amplifiers. By engineering the resonator in the manner described
here, this enables us to circumvent predicted scaling limits and offers the possibility to achieve a highly phased state for
a large number of fiber lasers in such an array. Experimental results are presented, the model of operation is discussed,
and scaling predictions are presented.
Proc. SPIE. 3590, Lasers in Surgery: Advanced Characterization, Therapeutics, and Systems IX
KEYWORDS: Laser therapeutics, FDA class I medical device development, Tissues, Surgery, Ultrasonography, Laser energy, Laser development, Semiconductor lasers, Laser tissue interaction, Laser systems engineering
We have developed a new device to effectively and quickly stop bleeding. The new device uses a small, 5 W diode laser to heat-up the tip of a modified medical forceps. The laser beam is totally contained within a protective enclosure, satisfying the requirements for a Class I laser system, which eliminates the need to protective eyewear. The new device is used in a manner similar to that of a bipolar electrocautery device. After visual location, the bleeding site or local vessel(s) is grabbed and clamped with the tips of the forceps-like instrument. The laser is then activated for a duration of typically 5 sec or until traditional visual or auditory clues such as local blubbling and popping indicate that the targeted site is effectively cauterized. When the laser is activated, the tip of the instrument, thus providing hemostasis. The new device was evaluated in animal models and compared with the monopolar and bipolar electrocautery, and also with the recently developed ultrasound technology. It has new been in clinical trials for abdominal surgery since September 1997.
Efficient coupling of high power lasers to optical fibers is desired for many applications. An example of these applications is the medical market, where coherent optical power delivered through fibers is used to perform state-of- the-art surgery. We report an efficient method for coupling optical energy from a laser-diode bar to a fiber. This method uses a single surface collimator combined with a two- surface optical transformer. An array of corrector lenses was used to assure that the output of the collimator was appropriately incident on the transformer. Optical efficiency of the collimator, after AR coating, is about 85 percent. The gratin design of the transformer is based on 4- phase level binary optics blazed grating with minimum feature size of 1.5 micrometers . Test results indicate that all the design aspects of our collimator and optical transformer are as expected, and experimental data are well within theoretical expectations. The average tested diffraction efficiency of the optical transformer is as high as 72 percent for one surface. Considering standard 0.8 micrometers process, the efficiency of the transformer for one surface can increase to > 92 percent. To our knowledge, this is the first practical demonstration of the optical transformer concept. These results demonstrate a low-cost and reliable method for efficient coupling of high power laser arrays to fibers for medical and industrial applications.
One significant cause of death during a sever trauma (gun wound or stab wound) is internal bleeding. A semiconductor diode laser system has been used in in vitro studies of cauterizing veins and arteries to stop bleeding. The conditions of laparoscopic surgery, including bleeding conditions (blood flow and pressure), are simulated. Results have been obtained both with and without using a hemostat (e.g., forceps) to temporarily stop the bleeding prior to the cautery. With the hemostat and a fiber-coupled 810-nm laser, blood vessels of up to 5 mm diameter were cauterized with an 8 W output from the fiber. Great cautions must be used in extrapolating from these in vitro results, since the exact conditions of bleeding in a living being are impossible to exactly reproduce in a laboratory in-vitro experiment. In a living being, when blood flow stops the cessation of nourishment to the vessels results in irreversible physiological changes. Also, the blood itself is different from blood in a living being because an anti-clotting agent (heparin) was added in order to inhibit the blood's natural tendency to coagulate.
While many colon cancers are curable, curability relates closely to stage. Once disease is spread beyond the confines of the colon and adjacent lymph nodes, cure is clearly the exception rather than the rule. Recently, surgical resection of solitary liver metastases has been effective in treatment of colon cancer, producing long term survival in approximately 20% of treatable patients. Surgery, however, is technically complex and there is a high perioperative morbidity and substantial perioperative mortality. For patients with multiple hepatic metastases in whom surgical extirpation is not possible, the outlook is dismal. Other modalities including chemotherapy have also resulted in limited success. Recently, a number of investigators have evaluated the effect of low power interstitial Nd:YAG laser irradiation for inducing hyperthermia and coagulative necrosis is hepatic tissue. In treating multiple or large hepatic metastases, the use of a lower power (1 - 5 watts), long duration (50 - 2400 seconds), single fiber laser delivery system has limitations. A computer controlled continuous wave Nd:YAG (1064 nm) laser system using a single fiber 'coupled' to a multiple array of fibers (4 to 6) has been developed for the delivery of low power laser irradiation to hepatic tissue. The advantage of laser energy being delivered simultaneously through multiple fibers is that it expands the area of tissue that can be treated over a given time. Through the use of interventional techniques including percutaneous ultrasound and/or CAT scan directed treatment, laser induced interstitial hyperthermia for large or multiple metastatic lesions could be initiated without the morbidity associated with open surgical procedures.