Cutting Edge Optronics (CEO) recently built and tested one of their industry standard REA diode-
pumped solid-state (DPSS) laser modules with an Er:YAG rod as the gain medium and pumped with in-house-manufactured 97Xnm laser diodes. The Er:YAG rod was provided by Northrop Grumman
SYNOPTICS. The module’s laser emission wavelength is 2.94μm, which is highly absorbed by water
and hydroxyapatite. A laser at this wavelength has a variety of applications in the medical and
scientific laser communities such as dental surgery, wart removal, the cutting of bone and soft
tissue, as well as for pumping mid-wave IR lasers.
Test results from an REA module with a 5mm diameter rod and quasi-continuous-wave (QCW)
pumping of the laser diodes are shown below. The gain of Er:YAG is much lower than typical Nd:YAG
systems. The best output coupler reflectivity to maximize output power was 95% in a short cavity of
280mm length with a flat high reflector. Fluorescence imaging of the 2.94um emission showed
good uniformity of absorbed diode light (see Figure 1.) Imaging the output coupler, a uniform beam
profile was observed (see Figure 2.)
Figure 3 shows output energies per pulse obtained during short cavity testing for various pulse
widths. With the same duty cycle, the module was tested at 500μs, 1ms, and 1.5ms. EƯiciencies of
pump energy to output energy of 19%, 22%, and 18% were obtained for 500μs, 1ms, and 1.5ms
respectively. The energy level dynamics of the Er:YAG system is complex. Due to thermally driven
eƯects, the tail end of the optical pulse fell oƯ for pulse widths longer than 1ms. This explains the
reduction in eƯiciency for 1.5ms pulses. At 15Hz and 1ms, a maximum average output power of
70W was obtained. The maximum output energies per pulse obtained for 500μs, 1ms, and 1.5ms
were 2J, 4.67J, and 5.66J, respectively.
Due to the high quantum defect in Er:YAG, thermal lensing is an important consideration when
building an Er:YAG laser. The power of the thermal lens in this module was measured to be 0.012
diopters per watt of average pump power plus a baseline of 0.173 diopters above the threshold.
The successful testing of a new Er:YAG, 5mm diameter side pumped rod laser module was
performed, with output pulse energies of up to 5.5J and average powers exceeding 50W achieved.
This module is based on the CEO’s industry-proven REA laser module series designs used for the past
several decades as oscillators and amplifiers in a variety of DPSS laser applications. These
modules are typically rated for lifetimes greater than 10 billion pulses, which exceeds the projected
lifetime of medical equipment in many environments.
Approved for Public Release: NG25-0073. @ 2025 Cutting Edge Optronics, Inc.
