Rick K. Nubling

OPTICAL PROPERTIES OF SINGLE-CRYSTAL SAPPHIRE FIBERS

Single-crystal sapphire fibers have been grown with the laser-heated pedestal-growth method with losses as low as 0.3 dB /m at 2.94 ?m. With the incorporation of a computer-controlled feedback system, fibers have been grown with less than +/-0.5 % diameter variation, or +/-1.5 ?m for a 300- ?m fiber. The losses in these fibers have been reduced further through a postgrowth anneal at 1000 degrees C in air, from 5.4 to 1.5 dB /m at 543 nm and from 0.4 -0.3 dB /m at 2.94 ?m. These fibers delivered 4.7 W at 10 Hz of Er:YAG laser power.

Launch conditions and mode coupling in hollow- glass waveguides

The attenuation and input end heating of hollow-glass waveguides are greatly affected by the way in which the input laser energy is coupled into the guides. A theoretical discussion of coupling conditions is related to waveguide loss and local heating, which can occur when the coupling is not optimized. Our results indicate that the optimum coupling for maximum transmission is not necessarily equiva- lent to optimum coupling to the lowest order HE11 mode. Additionally, it is shown that the input end heating of these waveguides can be reduced substantially with minimal effect on transmission if the waveguide bore size is large.

Optical properties of clad and unclad sapphire fiber

Single-crystal sapphire fibers have been grown, using the laser heated pedestal technique, with losses as low as 0.7 dB/m and with lengths up to 150 cm. We have applied polymer and sol- gel coatings to the fibers and we have evaluated the performance of these coatings as optical cladding. The best coating seems to be teflon AF even though the coatings are reasonably thin and low temperature.

Single-Crystal Laser-Heated Pedestal-Growth Sapphire Fibers for Er:YAG Laser Power Delivery.

The Er:YAG laser-induced damage (LID) threshold and modal properties of single-crystal sapphire fibers grown by the laser-heated pedestal-growth method have been measured. The lowest loss (~0.4-dB/m) sapphire fibers produce little mode mixing and therefore deliver a near-single-mode output profile if the Er:YAG laser input beam profile is also nearly Gaussian. Normally, however, Er:YAG laser output beam profiles are multimode with numerous high-energy spikes. This leads not only to a multimode output from the fiber but also increased fiber loss that is due to higher-order mode coupling. The results of LID testing give a damage fluence of ~1.4 kJ/cm(2) for 300-mum core-only sapphire fibers at 2.94 mum.

Optical properties of LHPG sapphire fibers

Sapphire optical fibers have been grown using the laser-heated pedestal-growth method with losses as low as 0.3 dB/m at 2.94 micrometers and lengths as long as 5 m. With the incorporation of a computer-controlled feedback system we have been able to grow fibers with less than plus or minus 0.5% diameter variation, or plus or minus 1.5 micrometers for a 300 micrometer fiber. We have been able to decrease the loss in these fibers through a post-growth anneal at 1000 degrees Celsius in air; from 5.4 dB/m to 1.5 dB/m at 543 nm and from 0.4 dB/m to 0.3 dB/m at 2.94 micrometer. These fibers delivered 4.7 W at 10 Hz of Er:YAG laser power.

Hollow Waveguides For CO2 Laser Delivery Systems

A hollow waveguide made from alumina, ceramic tubing has been developed for use in delivering CO2 laser power in laser surgical applications. This hollow fiber is rigid and can deliver in excess of 70 watts of power with spot sizes less than 1 mm. The output beam is nearly TEMoo. with a full divergence angle of less than 3°. The attenuation of the hollow fibers varies from 0.4 to 1.5 dB/m depending on bore size. Using a special coupler, we attach the waveguides to the articulated arm of a CO2 laser. The fiber is then inserted into an endoscope for delivering power into the body.

In-situ fiber optic FTIR spectroscopy for coal liquefaction processes

The development of diagnostic instrumentation for monitoring coal liquefaction process streams is discussed. A sapphire optical fiber was used as an attenuated total reflectance (ATR) element in conjunction with Fourier transform infrared (FT-IR) spectrometry to probe harsh liquefaction process streams. ATR provides a short, reproducible pathlength which allows for the analysis of highly absorbing materials, such as liquid hydrocarbons, and the properties of sapphire are well suited for the analysis of high temperature and high pressure process streams. A test cell was constructed which allowed in-situ monitoring of coal liquefaction reactions at 400 degree(s)C and 3000 psig. The cell incorporated a sapphire optical fiber as an ATR sensing element which was coupled to an FT-IR spectrometer using zirconium fluoride fiber optic cables. The spectra provide qualitative information about the liquefaction process.

Thermal and modal properties of hollow glass waveguides

The transmission and input end heating of hollow-glass waveguides are greatly affected by the launch conditions of the input laser energy. A theoretical discussion is given on the effect of coupling conditions from a carbon-dioxide laser and its effect on waveguide performance. It is shown that the optimum coupling for maximum transmission is not necessarily equivalent to optimum coupling to the lowest- order HE11 mode. It is also shown that the input end heating of these waveguides can be reduced substantially with minimal effect on transmission if the waveguide bore size is large.

Sapphire fibers for 3-μm delivery systems

Er:YAG laser energy is highly absorbed by water, and therefore can provide excellent cutting precision with minimal thermal damage to surrounding tissue. Single crystal sapphire fibers are capable of transmitting Er:YAG laser energy with low loss and, additionally, they are chemically durable and bio-compatible. In this study, 300 micrometers diameter sapphire fibers were evaluated for use in surgical applications. Scattering and absorption losses, effective NA, and power handling capabilities were measured. The fibers had losses less than 1 dB/m, an effective NA of 0.2, and damage thresholds exceeding 1.2 kJ/cm2. The high damage thresholds were achieved only after a laser conditioning process at the proximal end of the fiber.

Hollow sapphire fiber system for high-power CO2 lasers

Hollow sapphire fibers have been used to deliver up to 1500 W of CO2 laser power for industrial laser applications. These hollow waveguides incorporate a water jacket to prevent overheating. The fibers are about 110 cm in length and they have been bent to 90 degree(s). The bending loss for the large 1070-micrometers bore fiber is less than 15% of the straight loss.