Abstract We demonstrate a master oscillator power amplifier system that emits single-frequency, high-energy optical pulses at 1539 nm using an Er, Yb:glass planar waveguide amplifier with a normalized frequency of the waveguide of 4.4. A maximum pulse energy of 9.7 mJ is observed at a repetition frequency of 500 Hz. The signal to noise ratio is 25 dB and is independent of the repetition frequency from 100 to 500 Hz. The beam quality factor M 2 of the output is 1.03 thanks to the small normalized frequency of the planar waveguide.