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This program is funded by the National Science Foundation through grant number PHY-1157044.  Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Increasing Efficiency of Fiber Optics with a 178 Degree Axicon

In this project we are using a special lens called an axicon. The axicon is a lens that is flat on the back and cone shaped in the front (pictured on the home page). This type of lens when properly aligned produces a special beam called a Bessel Beam which is a beam that is made up of a series of rings as shown below in figure one.

Figure 1: Bessel Beam

We are then going to attempt to send or couple this Bessel Beam through a hollow core fiber. The reason we want to couple into a fiber with a Bessel Beam is because the natural mode or type of beam produced in a fiber is Bessel like. Thus, we theorize that if we send a Bessel Beam into a fiber we will not lose as much of the beam since the beam is already Bessel like and we can increase the efficiency through the fiber with few cycle short wavelength pulse laser light.

Now, there is a difficulty to this. The fiber is only 250 microns (a micron is 10^-6 meters) in diameter. Thus, we have to get a natural Bessel Beam down to less than 250 microns in order to couple through the fiber.

Difference Frequency Generation

In this project we are attempting to create a process called Difference Frequency Generation (DFG). This process takes two beams called the signal beam and idler beam and sends them together through an AgGaS2 crystal (silver thiogallate) and produces a low energy beam with a huge wavelength. We are hoping to create a 1 mJ beam from DFG to use for other experiments that need larger wavelengths. This will be a struggle, however, because of the low energies that are produced. Figure 2 below shows how the energy of the DFG beam relates to the signal and idler beams.

Figure 2: Conservation of Energy with DFG

Our goal is to genearate intense mid-IR (5 – 10 micron) few cycle pulse waves at higher powers than ever before.