Monolithic polarization maintaining fiber chirped pulse amplification (CPA) system for high energy femtosecond pulse generation at 1.03 µm.

A monolithic polarization maintaining fiber chirped pulse amplification system with 25 cm Yb(3+)-doped high efficiency media fiber that generates 62 µJ sub-400 fs pulses with 25 W at 1.03 µm has recently been demonstrated.

Monolithic fiber chirped pulse amplification system for millijoule femtosecond pulse generation at 1.55 µm.

A monolithic fiber chirped pulse amplification system that generates sub-500 fs pulses with 913 µJ pulse energy and 4.4 W average power at 1.55 µm wavelength has recently been demonstrated. The estimated peak power for the system output approached 1.9 GW. The pulses were near diffraction-limited and near transform-limited, benefiting from the straight and short length of the booster amplifier as well as adaptive phase shaping for the overall mitigation of the nonlinear phase accumulation. The booster amplifier employs an Er(3+)-doped large mode area high efficiency media fiber just 28 cm in length with a fundamental mode (LP(01)) diameter of 54 µm and a corresponding effective mode area of 2290 µm(2).

Root cause analysis and solution to the degradation of wavelength division multiplexing (WDM) couplers in high power fiber amplifier system.

In the evaluation a fused biconical taper 1480/1580 nm WDM's ability to handle high power cascaded Raman laser throughput (>100 W) a significant degradation in performance was observed. A systematic root cause investigation was conducted and it is experimentally confirmed that the WDM degradation was caused by an interaction between the high power 1480 nm line, an out-of-band Stokes line, and the -OH content of the glass optical fiber. Slanted fiber Bragg grating (SFBG) was introduced to filter out the 1390 nm out-of-band Stokes line in an attempt to avoid this interaction. Ultimately a series of tests were conducted and it was confirmed that the addition of a 1390 nm SFBG in between a high power Raman laser and the high power WDM has successfully prevented the degradation which therefore allowed the continued high power operation of the WDM. NAVAIR Public Release SPR 2013-469 Distribution Statement A-"Approved for Public release; distribution is unlimited".

Higher-order mode fiber enables high energy chirped-pulse amplification.

Energy scaling of femtosecond fiber lasers has been constrained by nonlinear impairments and optical fiber damage. Reducing the optical irradiance inside the fiber by increasing mode size lowers these effects. Using an erbium-doped higher-order mode fiber with 6000 µm(2) effective area and output fundamental mode re-conversion, we show a breakthrough in pulse energy from a monolithic fiber chirped pulse amplification system using higher-order mode propagation generating 300 µJ pulses with duration <500 fs (FWHM) and peak power >600 MW at 1.55 µm. The erbium-doped HOM fiber has both a record large effective mode area and excellent mode stability, even when coiled to reasonable diameter. This demonstration proves efficacy of a new path for high energy monolithic fiber-optic femtosecond laser systems.

High efficiency, monolithic fiber chirped pulse amplification system for high energy femtosecond pulse generation.

A novel monolithic fiber-optic chirped pulse amplification (CPA) system for high energy, femtosecond pulse generation is proposed and experimentally demonstrated. By employing a high gain amplifier comprising merely 20 cm of high efficiency media (HEM) gain fiber, an optimal balance of output pulse energy, optical efficiency, and B-integral is achieved. The HEM amplifier is fabricated from erbium-doped phosphate glass fiber and yields gain of 1.443 dB/cm with slope efficiency >45%. We experimentally demonstrate near diffraction-limited beam quality and near transform-limited femtosecond pulse quality at 1.55 µm wavelength. With pulse energy >100 µJ and pulse duration of 636 fs (FWHM), the peak power is estimated to be ~160 MW. NAVAIR Public Release Distribution Statement A-"Approved for Public release; distribution is unlimited".

Design and fabrication of hollow-core photonic crystal fibers for high-power ultrashort pulse transportation and pulse compression.

We report on the recent design and fabrication of kagome-type hollow-core photonic crystal fibers for the purpose of high-power ultrashort pulse transportation. The fabricated seven-cell three-ring hypocycloid-shaped large core fiber exhibits an up-to-date lowest attenuation (among all kagome fibers) of 40 dB/km over a broadband transmission centered at 1500 nm. We show that the large core size, low attenuation, broadband transmission, single-mode guidance, and low dispersion make it an ideal host for high-power laser beam transportation. By filling the fiber with helium gas, a 74 µJ, 850 fs, and 40 kHz repetition rate ultrashort pulse at 1550 nm has been faithfully delivered at the fiber output with little propagation pulse distortion. Compression of a 105 µJ laser pulse from 850 fs down to 300 fs has been achieved by operating the fiber in ambient air.

High average power, high energy 1.55 µm ultra-short pulse laser beam delivery using large mode area hollow core photonic band-gap fiber.

We demonstrate high average power, high energy 1.55 µm ultra-short pulse (<1 ps) laser delivery using helium-filled and argon-filled large mode area hollow core photonic band-gap fibers and compare relevant performance parameters. The ultra-short pulse laser beam-with pulse energy higher than 7 µJ and pulse train average power larger than 0.7 W-is output from a 2 m long hollow core fiber with diffraction limited beam quality. We introduce a pulse tuning mechanism of argon-filled hollow core photonic band-gap fiber. We assess the damage threshold of the hollow core photonic band-gap fiber and propose methods to further increase pulse energy and average power handling.

Suppression of mode partition noise in a multiwavelength semiconductor laser through hybrid mode locking.

We demonstrate the suppression of intensity fluctuations, which are known as mode partition noise, in a multiwavelength semiconductor laser by using a hybrid mode-locking scheme. The laser design incorporates a saturable absorber and a gain-modulated semiconductor optical amplifier, along with spectral filtering, in an external cavity to achieve multiwavelength hybrid mode locking. The mode-locked laser produces an error-free (pulse Q>13) 300-MHz optical pulse train in each of three wavelength channels.