Photonic lantern kW-class fiber amplifier.

Pump-limited kW-class operation in a multimode fiber amplifier using adaptive mode control and a photonic lantern front end was achieved. An array of three single-mode fiber inputs was used to adaptively inject the appropriate superposition of input modes in a three-mode gain fiber to achieve the desired mode at the output. Mode fluctuations at high power were compensated by adjusting the relative phase, amplitude, and polarization of the single-mode fiber inputs. The outlook for further power scaling and adaptive-optic compensation is described.

Diffractive coherent combining of a 2.5 kW fiber laser array into a 1.9 kW Gaussian beam.

Five 500 W fiber amplifiers were coherently combined using a diffractive optical element combiner, generating a 1.93 kW beam whose M(2)=1.1 beam quality exceeded that of the inputs. Combining efficiency near 90% at low powers degraded to 79% at full power owing to thermal expansion of the fiber tip array.

Sub-picosecond pulses at 100 W average power from a Yb:YLF chirped-pulse amplification system.

We present a high-repetition-frequency, diode-pumped, and chirped-pulse amplification system operating at 106 W average output power with excellent beam quality (M(2)=1.3), based on cryogenically cooled Yb:YLF. 1 nJ seed pulses, derived from a mode-locked Ti:sapphire laser, are first amplified to 1 mJ pulse energy at 10 kHz repetition frequency in a regenerative amplifier. The second-stage, multipass amplifier increases the pulse energy to 10.6 mJ, resulting in a spectral width of 2.2 nm. The pulses are compressed to 865 fs in duration, which is 1.26 times the transform limit.

Picosecond pulses from a cryogenically cooled, composite amplifier using Yb:YAG and Yb:GSAG.

A cryogenic Yb amplifier using two laser materials, Gd3Sc2Al3O12 and Y3Al5O12 (YAG), has been used to obtain 70 W average power at 5 kHz pulse repetition frequency; the output was compressed to 1.6 ps, compared with an input compressible to 1.4 ps. The gain broadening obtained by combining two media enables shorter pulses than using Yb:YAG alone but retains the power-scaling advantages of cryogenic Yb:YAG.

Power scaling of cryogenic Yb:LiYF(4) lasers.

We demonstrate a cryogenically cooled Yb:LiYF(4) (Yb:YLF) laser with 224W linearly polarized output power (pump-power limited) and a slope efficiency of 68%. The beam quality is characterized by an M(2) approximately 1.1 at 60W output and M(2) approximately 2.6 at 180W output. This level of average laser power is approximately 2 orders of magnitude higher than demonstrated previously in cryogenic Yb:YLF. Yb:YLF is attractive for femtosecond pulse generation because of its wide gain bandwidth, and this demonstration shows the potential for high-average-power subpicosecond pulse lasers.

250 mW, 1.5 microm monolithic passively mode-locked slab-coupled optical waveguide laser.

We report the demonstration of a 1.5 microm InGaAsP mode-locked slab-coupled optical waveguide laser (SCOWL) producing 10 ps pulses with energies of 58 pJ and average output powers of 250 mW at a repetition rate of 4.29 GHz. To the best of our knowledge, this is the first passively mode-locked slab-coupled optical waveguide laser. The large mode and low confinement factor of the SCOWL architecture allows the realization of monolithic mode-locked lasers with high output power and pulse energy. The laser output is nearly diffraction limited with M2 values less than 1.2 in both directions.

165-W cryogenically cooled Yb:YAG laser.

Thermo-optic distortions often limit the beam quality and power scaling of high-average-power lasers. Cryogenically cooled Yb:YAG is used to efficiently generate 165 W of near-diffraction-limited beam from a power oscillator with negligible thermo-optic effects. End pumped with 215 W of incident pump power from two diode modules, the laser has an optical-optical efficiency of 76%, a slope efficiency of 85%, and an M2 value of 1.02.