Danh C. Tran

Immobilization of radwastes in glass containers and products formed thereby

This invention relates to the immobilization of toxic materials, e.g., radioactive materials, in glass for extremely long periods of time. Toxic materials, such as radioactive wastes, which may be in the form of liquids, or solids dissolved or dispersed in liquids or gases, are deposited in a glass container which is heated to evaporate off non-radioactive volatile materials, if present; to decompose salts, such as nitrates, if any, and to drive off volatile non-radioactive decomposition products, and then to collapse the walls of said container on said radwaste and seal the container and immobilize the contained radwaste, and then burying the resulting product underground or at sea. In another embodiment, the glass container also contains glass particles, e.g., spheres or granules, on which the radwaste solids are deposited. In other embodiments, the glass container can be made of porous glass or non-porous glass, and/or the contained glass particles can be made of porous or non-porous glass or mixtures of porous or non-porous glass, and/or the glass container can be open at one end and closed at the other or open at both ends, and/or the glass container can be closed at one end with a porous or non-porous closure and open at the other end or closed at the other end with a porous closure. When a porous glass container and/or porous glass particles are used, the radwaste deposits within the pores of the glass which are closed during the subsequent heating step after non-radioactive volatiles have been driven off and prior to sealing the container. There results a substantially impervious glass article in which the radwaste is entrapped and which is highly resistant to leaching action. The products resulting from the use of porous glass, as the container, contents, or both, can be used as sources of radioactivity for a variety of applications in medicine, sterilization, food preservation and any other application where radiation can be beneficially employed.

Mid-IR Germanium Oxide Fibers for Contact Erbium Laser Tissue Ablation in Endoscopic Surgery

Endoscopic surgical applications of erbium lasers have been limited due to the lack of a suitable mid-IR optical fiber delivery system. Germanium oxide fibers are used for noncontact tissue ablation, but are not recommended for contact tissue ablation applications typically required during endoscopic surgery. This study describes the assembly and characterization of hybrid mid-IR fibers consisting of germanium oxide trunk fibers and sapphire fiber tips, and side-firing germanium oxide fibers with either 45deg angled tips or micromirrors. Average powers up to 8.5 W (850 mJ at 10 Hz) and transmission up to 70% was demonstrated through 450-mum-core, 1.5-m-long fibers, sufficient for endoscopic laser ablation of soft and hard tissues in contact mode.

Progress toward an athermal HEL optical window

Progress in the development phases of a new optical material that exhibits very low thermal lensing and robustness against thermal shock will be reported. Material, thermal, and optical properties of the current material formulation, called OFG-04, have been determined on small- and mid-scale samples. Manufacture scale-up to full-scale has been completed and flight windows prepared. Follow-on efforts are now beginning for an optimized formulation that will exhibit even lower bulk absorptance and OPD change with temperature rise.

Development of low-OPD windows for airborne laser

We begin with a brief review of prior work relating to optical windows for use with high power laser beams. A typical window must provide pressure separation between system segments, ultra-low loss, and small wavefront distortion of the many outgoing laser beams and signal returns despite heating by the high energy laser beam. Historically, two approaches have been examined to improve such windows.

Infrared-fiber-coupled acousto-optic tunable filter spectrometer

We have developed an Improved spectrometer using the acousto-optic tunable filter (AOTF) to obtain high speed spectroscopic data. The fIlter has been used with infrared transmitting fluoride glass fibers for remote spectroscopy. The AOTF Is made from tellurium dioxide, and can be configured to operate anywhere from 360 nm to 5 microns. Potential applications Include medical diagnostIcs, chemical process control, and spectral imaging.

Mid-IR Germanium Oxide Fibers for Erbium:YAG and Erbium:YSGG Contact Laser Tissue Ablation in Endourology

Endoscopic surgical applications of Erbium:YAG and Erbium:YSGG lasers have been limited due to the lack of a suitable mid-IR optical fiber delivery system. Germanium oxide fibers are currently used in the clinic for non-contact tissue ablation, but are not recommended for contact tissue ablation applications typically required during endoscopic surgery in a fluid environment. This study describes the assembly and characterization of hybrid mid-IR fibers consisting of germanium oxide trunk fibers and sapphire fiber tips, and side-firing germanium oxide fibers with either 45° angled fiber tips or micro-mirrors. Average powers up to 8.5 W (850 mJ at 10 Hz) and transmission up to 70% was demonstrated through 450-μm-core, 1.5-meter-long fibers, sufficient for endoscopic laser ablation of soft and hard tissues in contact mode.

Transmission of high Erbium:YAG laser pulse energies through germanium oxide trunk fibers with sapphire tips

Endoscopic applications of the Erbium:YAG laser have been limited due to the lack of a suitable optical fiber delivery system. This study compares the transmission of Er:YAG laser radiation through germanium oxide trunk fibers with silica or sapphire fiber tips for potential use in endoscopic tissue ablation. Er:YAG laser radiation with a wavelength of 2.94 &mgr;m, pulse length of 300 &mgr;s, pulse energies of 5-1360 mJ, and pulse rates of 3-10 Hz, was delivered through 1-m-long germanium oxide fibers with either 1-cm-long, 550-&mgr;m-diameter silica or sapphire tips. Transmission through the germanium oxide / sapphire fibers measured 65 + 5 % compared with 55 + 4 % for the germanium oxide / silica fibers (P < 0.05). The damage threshold for the hybrid fibers averaged 309 + 44 mJ and 126 + 43 mJ, respectively (n = 7 fibers each) (P < 0.05). Maximum pulse energies transmitted through the fibers were 700 mJ and 220 mJ, respectively. Improved index-matching of the trunk fiber and fiber tip at 2.94 &mgr;m resulted in higher transmission and damage thresholds for the germanium oxide / sapphire fibers. The germanium oxide / sapphire fiber may represent a promising mid-IR optical fiber delivery system for use in endoscopic applications of the Er:YAG laser requiring a flexible, biocompatible, and robust fiber delivery system for contact tissue ablation.

Optical and surface properties of oxyfluoride glass

Using conventional materials like fused silica and sapphire for critical window components in a high-power laser system can lead to intolerable thermal distortions and optical path difference effects. A new oxyfluoride glass is being developed which has the unique property of possessing a negative thermo-optic coefficient (dn/dT) in the near- and mid-wave infrared. Specifically, the refractive index (n) of oxyfluoride glass decreases as the temperature increases. The distortions caused by thermal expansion of the glass during laser irradiation are partly offset by the negative dn/dT. This paper specifically addresses optical properties and surface finishing of oxyfluoride glass compared to fused silica. Normarski micrographs and surface profiles were measured to inspect the surface quality since smooth surfaces are essential for suppressing surface scattering and absorption. The refractive index and thermo-optic coefficient were measured using null polarimetry near the Brewster angle. Low dn/dT is required for laser windows. Transmittance spectra were measured to deduce the extinction coefficient by comparing with the transmittance calculated from the refractive index and to screen for unwanted absorption from contaminants including hydrocarbon oils, polishing residue, and water or -OH groups. Total integrated scattering was measured for both surface and bulk scattering. All measurements were done on 1.0- and 1.5-inch-diameter witness samples.

AOTF spectrometer for gas analysis

The acousto-optic tunable filter (AOTF) spectrometer has been used to measure various gases of clinical interest using infrared spectroscopy. The AOTF is a birefringent crystal capable of high speed, random wavelength access. Various crystals can cover the range from 250 nm to 5 microns. Infrared transmitting fibers have been used for remote diagnostics of carbon dioxide and anesthesia gas. We will report on system specifications such as sensitivity, noise, and drift.