David A. Rockwell

Near-diffraction-limited operation of step-index large-mode-area fiber lasers via gain filtering

We present, for the first time to our knowledge, an explicit experimental comparison of beam quality in conventional and confined-gain multimode fiber lasers. In the conventional fiber laser, beam quality degrades with increasing output power. In the confined-gain fiber laser, the beam quality is good and does not degrade with output power. Gain filtering of higher-order modes in 28microm diameter core fiber lasers is demonstrated with a beam quality of M(2)=1.3 at all pumping levels. Theoretical modeling is shown to agree well with experimentally observed trends.

Er-doped high-aspect-ratio core rectangular fiber producing 5 mJ, 13 ns pulses at 1572 nm

We have produced 5 mJ, 13 ns pulses using a very large-mode-area rectangular fiber containing a high-aspect-ratio core with dimensions of ~30 μm×580 μm. The rectangular fiber design retains a thin cladding dimension ~0.5 mm, which is compatible with a compact coiled package. We have developed a theoretical model that achieves good agreement with the experimental data. This model indicates that an optimized fiber design can be scaled to pulse energies of several tens of millijoules. We also discuss a strategy for maintaining good beam quality in both transverse dimensions of this fiber.

Er-doped high aspect ratio core (HARC) rectangular fiber producing 5-mJ, 13-nsec pulses at 1572 nm

We demonstrated 5-mJ, 13-nsec pulses using a diode-pumped high-aspect ratio core (HARC) fiber with an active area of 30 x 580 μm2, in good agreement with our model, which predicts scalability to several 10s of mJ.

330-W, 1030-nm coherent LADAR transmitter with a 4-kHz linewidth

We describe a hybrid narrowband fiber-slab laser system that produced 330 W CW output power at 1030 nm with a frequency bandwidth of 4 kHz and an average beam quality of 1.9 times diffraction-limited.

2-kW Average Power CW Phase-Conjugate Solid-State Laser

We have demonstrated stable operation of a 2-kW Yb:YAG phase-conjugate master oscillator power amplifier (PC-MOPA) laser system with a loop phase-conjugate mirror (LPCM). This is the first demonstration of a continuous wave (CW)-input LPCM MOPA operating at a power greater than 1 kW with a nearly diffraction-limited output beam. The single-pass beam quality incident on the LPCM varied with the specific operating conditions, but it was typically ~20 times diffraction-limited (XDL). The measured beam quality with an MOPA output power of 1.65 kW was 1.3 XDL.

2-kW average power phase-conjugate master oscillator power amplifier

We have demonstrated stable operation of a 2-kW Yb:YAG phase-conjugate master oscillator, power amplifier (PC-MOPA) laser system with a loop phase-conjugate mirror (LPCM). This is the first demonstration of a CW-input LPCM MOPA operating at a power greater than 1 kW with a nearly diffraction-limited output beam. The single-pass beam quality incident on the LPCM varied with the specific operating conditions, but it was typically ~ 20 times diffraction-limited (XDL). The measured beam quality with a MOPA output power of 1.65 kW was 1.3 XDL.

A Master-Oscillator-Power-Amplifier 2-micron Laser Using Fiber Phase-Conjugate Mirror

For the first time, a 2-micron master-oscillator-power-amplifier laser using a fiber based phase conjugation mirror has been demonstrated. The beam quality improvement and 56% of the PCM reflectivity have been achieved.

Phase-Conjugated 2-μm Laser System

For the first time, beam quality improvement of 2 μm laser using fiber based phase conjugation mirror has been demonstrated. Single frequency operation is necessary to lower threshold. The reflectivity of the PCM is ~50%.

Phase-conjugate solid-state lasers

This tutorial reviews phase conjugation as applied to solid-state lasers, beginning with early demonstrations of enhanced beam quality, power scalability, and system-level benefits, and concluding with ongoing efforts striving toward multi-kilowatt powers.