Diamond Radiator Thinning Using an Excimer Laser

Important Documents

UConn Laser Safety Manual

Excimer laser S.O.P.

Oxford GP 2000 User Manual

Laser Thinning of Diamond

Current Excimer Laser to be brought online

Laser ablation will be used to thin the diamond chip to the precise thickness required for the radiator. An older excimer laser offered by a local AMO group will be converted from a XeCl 308 nm beam to the required ArF 193 nm beam. Although the system was last used 10 years ago, it was left in a fully functioning state and was properly flushed upon decomposition. There may also be another unused excimer laser that can be used for parts in case any repair is needed. I have included a link to my current Lab Journal which I plan to update bi weekly.

Excimer Laser

Specs on EMG 101 MSC excimer laser.

Gas Purification System

specs on GP2000

Figure: Average laser output as a function of total shots fired

Laser Beamline

laser optics

Rendering of ablation beamline

Ablation Rate

ablation rate

FORTRAN Simulations of Beam Spot

• A FORTRAN program has been written which simulates rays exiting the laser aperture and then propagating through a fused silica plano-convex lens. Using this program we can now observe the geometry of the beam as it passes through the focusing lens onto a target. We have seen that the beam leaving the laser aperture has a flat top distribution in the X plane and a Gaussian distribution in the Y. As the beam is focused both the X and Y projections achieve Gaussian distributions.

Original Beam Profile

Focused Beam Profile

• Taking the X and Y projections of the focused beam and fitting them with a Gaussian distribution,we are able to attain $\sigma _{X}=0.63mm\,$ and $\sigma _{Y}=0.23mm\,$.

X-axis Projection of Focused Beam

Y-axis Projection of Focused Beam

• Assuming a Gaussian distribution at the waist of the beam, we now find the FWHM (full width at half maximum) by the following relation,

$\mathrm {FWHM} =2{\sqrt {2\ln 2}}\ \sigma .$

• The smallest values of $\mathrm {FWHM_{X}}$ and $\mathrm {FWHM_{Y}}$ were 1.49mm and 0.552mm respectively.
• The Rayleigh Length, $\mathrm {Z_{R}}$ is defined as the distance from the beam waist along the axis of propagation to the point where its cross section is doubled ($\mathrm {\omega } _{R}$). This value represents the "play" we will have when trying to focus the beam onto the diamond target for ablation. Taking $\mathrm {\omega } _{0}$ as the beam waist, and using the $\mathrm {FWHM}$ as its value we are looking for the point where,

$\omega _{R}={\sqrt {2}}\ \omega _{0}.$

Describes the Rayleigh Length of a beam waist $\omega _{0}$.

• Plotting $\mathrm {\omega } _{R}$ as a function of distance away from the beam waist center, we find an average Rayleigh Length,

$\mathrm {Z_{RX}} =11.8mm$ and $\mathrm {Z_{RY}} =10.5mm$

Waist of Beam through X-axis

Waist of Beam through Y-axis

• Knowing $\mathrm {\omega } _{0}$ also allows us to calculate the theoretical fluence of the beam. Assuming maximum power of 220mJ over a 1.49mm x 0.552mm area yields $26J/cm^{2}.$ Which is above the $14J/cm^{2}$ threshold value cited by Brookhaven National Laboratories who were conducting diamond ablation experiments with a 213nm Nd:YAG laser (213nm with the use of a 4 + 1 frequency mixing crystal). Our ArF excimer laser produces 193nm light that will be more readily absorbed by the surface of the diamond as diamond is opaque to wavelengths above the band gap. These calculations provide a level of confidence that we theoretically will be able to ablate diamond.