MRI-Fiber Lasers

High Power Eye-Safe Fiber Lasers.

Army Office of Research
High Power Fiber Lasers

Program Summary

This program will advanced the development of high power eye-safe fibers laser through three novel approaches to large mode area fiber design

  1. high power fiber lasers based on ribbon geometries
  2. high power fiber lasers based photonic crystal geometries
  3. high power fiber lasers based on gain guiding.

These thrusts are complemented by two cross-cutting tasks focused on:

The program is largely based in Er- or Tm-doped fibers

Eye-Safe Lasers

Eye safe lasers are defined as lasers with output wavelengths sufficiently long as to be absorbed in the lens of the human eye, before the radiation is able to reach the retina. This protects the retina, a more sensitive component of the eye, from damage in the event of exposure to laser radiation. The nominal wavelength for a laser to be considered eye-safe is 1.4 microns. The emphasis on Erbium and Thulium fiber lasers is based on the need for high power, eye safe lasers as the emission wavelengths of both these laser ions is beyond the 1.4 micron threshold. Erbium is a fairly well understood ion, due to its frequent use in the telecommunications industry. It will prove useful in testing new concepts in fiber design without the need to also worry about understanding the properties of the ion doped glass itself. The wavelength of Erbium lasers are in the range of 1.54 microns and can be diode pumped by several wavelengths including 915, 940, and 976nm. Thulium is a less well known and studied dopant, but is promising in the realm of eye-safe fiber lasers due to its approximately 2 micron emission wavelength with a nearly 300nm emission spectrum around this value. More importantly is what is known as the “two for one” process in Thulium whereby one photon of pump light at around 793nm can be converted into two photons of laser light by what is known as a cross relaxation process between two Thulium ions. This process allows for high pump light conversion efficiency, allowing Thulium lasers to theoretically operate beyond its quantum defect limit of 40% to upwards of 80% slope efficiency. This is a significant advantage over the erbium fiber laser, which has no such cross relaxation process and is thus limited by its quantum defect to around 63% efficiency. Combining new and novel fiber designs with these ions will allow the scaling up to high power, single mode, eye safe laser sources.