Updated April 20, 2007
There is considerable interest in developing compact sources of light in the extreme ultraviolet portion of the electromagnetic spectrum. Thus far, the capabilities of extreme ultraviolet light remain relatively untapped. Extreme ultraviolet light is useful for numerous applications, such as high-resolution imaging, interferometry, and lithography. Research at the National Science Foundation's Engineering Research Center for Extreme Ultraviolet Science and Technology at Colorado State University is focused around creating compact sources of coherent extreme ultraviolet light.
The purpose of this project is to upgrade an existing extreme ultraviolet laser. The solutions to improve the current system are twofold. First, the third amplification stage of the laser is being upgraded to provide a larger energy pulse to the target. Because the energy output of the third amplification stage is being increased, all successive optics in the system must be replaced. Second, utilizing a mirror consisting of 5 steps, the traveling wavefront of the beam incident upon the target can be modified, such that the gain on the target is coincident. The redesign of this laser is a collaborative effort of students at the engineering research center, and this document will focus on my roles in the project.
The origin of the traveling wavefront delays can best be described with the aid of a simple diagram:
In the above diagram, there are two rays incident on a target of length L. Assuming that the incident rays are parallel, or nearly parallel, they have a path difference of D. This path difference is the result of the tilted angle that the rays strike the target at; if the rays struck the target at almost normal incidence, the length D would essentially go to zero.
The reason why this path difference is detrimental is because the gain created on the target has a limited lifetime. If the path difference of two rays is too large, the gain created from the energy of both rays will not be fully utilized, because the gain created by the second ray may already have disappeared by the time the pulse reaches that point on the target. Thus, by adding a step mirror to the focusing optics, the relative path difference can be modified to compensate for the time mismatch that results in the loss of gain. The calculations to achieve this compensation have an accuracy of ~0.30ps, while the gain has a lifetime of ~5.0ps. The implications of this are that to a very great accuracy the traveling wavefront delay can be compensated for.
April 2007: Completed optical test, calibrated flat for step mirror, and verified successful control of step mirror.
March 2007: LABVIEW implementation complete and tested. Optical test setup is designed.
December 2006: Semester I of senior design finishes, with the LABVIEW implementation a work in progress.
October 2006: Traveling wavefront calculations were completed. The compensation is within an accuracy of ~0.30ps, compared to a gain lifetime of ~5.0ps.
September 2006: The design of the focusing system is completed. It allows for a range of setups, from 23 to 45 degrees grazing incidence angle, with a target length of 4 to 8mm.
Here are some resources associated with the project.
I, Daniel Reinholz, am the only member of this team from the Senior Design class. However, I have been working in collaboration with other students at the engineering research center. In particular, I worked with Emilie Caboche in the design of the focusing optics, and I have worked with Diego Frongia in the LABVIEW implementation. Dale Martz, a graduate student, has been available to mentor me in progressing through this project. My advisor for the project is Dr. Jorge Rocca, and I would like to give thanks to him and all who have contributed to this project, including those not mentioned here.