Broad Bandwidth, All-fiber, Thulium-doped Photonic Crystal Fiber Amplifier for Potential Use in Scaling Ultrashort Pulse Peak Powers

Fiber based ultrashort pulse laser sources are desirable for many applications; however generating high peak powers in fiber lasers is primarily limited by the onset of nonlinear effects such as self-phase modulation, stimulated Raman scattering, and self-focusing. Increasing the fiber core diameter mitigates the onset of these nonlinear effects, but also allows unwanted higher-order transverse spatial modes to propagate. Both large core diameters and single-mode propagation can be simultaneously attained using photonic crystal fibers. Thulium-doped fiber lasers are attractive for high peak power ultrashort pulse systems. They offer a broad gain bandwidth, capable of amplifying sub-100 femtosecond pulses. The longer center wavelength at 2 ?m theoretically enables higher peak powers relative to 1 [micro]m systems since nonlinear effects inversely scale with wavelength. Also, the 2 [micro]m emission is desirable to support applications reaching further into the mid-IR. This work evaluates the performance of a novel all-fiber pump combiner that incorporates a thulium-doped photonic crystal fiber. This fully integrated amplifier is characterized and possesses a large gain bandwidth, essentially single-mode propagation, and high degree of polarization. This innovative all-fiber, thulium-doped photonic crystal fiber amplifier has great potential for enabling high peak powers in 2 [micro]m fiber systems; however the current optical-to-optical efficiency is low relative to similar free-space amplifiers. Further development and device optimization will lead to higher efficiencies and improved performance

2 Micron Fiber Lasers: Power Scaling Concepts and Limitations

Thulium- and holmium-doped fiber lasers (TDF and HDF) emitting at 2 micron offer unique benefits and applications compared to common ytterbium-doped 1 micron lasers. This dissertation details the concepts, limitations, design, and performance of four 2 micron fiber laser systems. While these lasers were developed for various end-uses, they also provide further insight into two major power scaling limitations. The first limitation is optical nonlinearities: specifically stimulated Brillouin scattering (SBS) and modulation instability (MI). The second limitation is thermal failure due to inefficient pump conversion. First, a 21.5 W single-frequency, single-mode laser with adjustable output from continuous-wave to nanosecond pulses is developed. Measuring the SBS threshold versus pulse duration enables the Brillouin gain coefficient and gain bandwidth to be determined at 2 micron. Second, a 23 W spectrally-broadband, nanosecond pulsed laser is constructed for materials processing applications. The temporally incoherent multi-kW peak power pulses can also efficiently produce MI and supercontinuum generation by adjusting the input spectral linewidth. Third, the measured performance of in-band pumped TDF and HDF lasers are compared with simulations. HDF displays low efficiencies, which is explained by including ion clustering in the simulations. The TDF operates with impressive \u3e 90% slope efficiencies. Based on this result, a system design for \u3e 1 kW average power TDF amplifier is described. The designed final amplifier will be in-band pumped to enable high efficiency and low thermal load. The amplifier efficiency, operating bandwidth, thermal load, and nonlinear limits are modeled and analyzed to provide a framework for execution. Overall, this dissertation provides further insight and understanding on the various processes that limit power scaling of 2 micron fiber lasers

Resonantly Pumped Amplification In A Thulium-Doped Large Mode Area Photonic Crystal Fiber

We demonstrate resonantly pumped amplification in a thulium-doped photonic crystal fiber. This enables greatly increased efficiencies compared to 795nm or 1550nm pumping and is attractive for pulsed amplification. © OSA 2015

Resonantly Pumped Amplification In A Thulium-Doped Large Mode Area Photonic Crystal Fiber

We demonstrate resonantly pumped amplification in a thulium-doped photonic crystal fiber. This enables greatly increased efficiencies compared to 795nm or 1550nm pumping and is attractive for pulsed amplification

Comparison Of In-Band Pumped Tm: Fiber And Ho: Fiber

Thulium and holmium have become the rare earth dopants of choice for generating 2 micron laser light in silica fiber. The majority of Tm: fiber lasers are pumped with high power diodes at 790nm and rely upon cross-relaxation processes to achieve optical-to-optical efficiencies of 55-65%. Tm: fiber lasers can also be pumped at \u3c1900nm by another Tm: fiber laser to minimize quantum defect, reaching efficiencies \u3e90%. Ho: fiber lasers are similarly pumped by Tm: fiber lasers at 1900-1950nm, with \u3c70% typical efficiency. In this work, Tm: fiber and Ho: fiber lasers are in-band pumped using the same experimental setup to directly compare their performance as 2 micron sources

Photonic Crystal Fiber Pump Combiner For High-Peak Power All-Fiber Thulium Lasers

We report on the performance of a prototype pump combiner for use with thulium-doped photonic crystal fiber (PCF). This platform is attractive for all-fiber high energy and high peak power laser sources at 2 μm. We will report on the performance of this integrated amplifier in comparison to free space amplification in Tm:PCF. In particular, we carefully look for spectral/temporal modulation resulting from multimode interference between fundamental and higher order transverse modes in the amplifier to evaluate this for ultrashort chirped pulse amplification. The slope efficiency for the all-fiber amplifier is 22.1 %, indicating the need for further improvement. However, an M2 \u3c 1.07 demonstrates excellent beam quality, as well as amplified polarization extinction ratios of ∼25 dB. © 2014 SPIE

Resonantly Pumped Amplification In A Thulium-Doped Photonic Crystal Fiber

Efficiencies \u3c50% are typical in large mode area, thulium-doped photonic crystal fibers when pumped at 790nm. These large thermal loads limit power scaling. In this work, we investigate resonant pumping and demonstrate slope efficiencies \u3e64%