High-speed, high-resolution materials processing strongly benefits from optical sources that deliver high peak power in
short, high-repetition-rate pulses of excellent beam quality. These sources are also of interest for achieving high average
power at nonlinearly-generated wavelengths. Until recently, high peak power, high-repetition-rate pulses have only been
available from solid-state lasers. Fiber lasers and amplifiers offer significant advantages over solid-state lasers in terms
of size and wall-plug efficiency. This paper presents a fiber-based master-oscillator/power-amplifier (MOPA) source at
1064nm featuring 84-μm-core, polarization-maintaining Yb-doped photonic crystal fiber that generates ~20ps - 100ps
pulses at variable pulse repetition frequencies (PRFs), from 10kHz to 100MHz. The flexibility in pulse format allows the
source to be tailored to the application. Where peak power is critical, the PRF is reduced to achieve maximum peak
power. Where average power is needed, the PRF is increased to achieve high average power. Peak powers of ~4MW
have been achieved at reduced PRF (100kHz), and average powers greater than 172W have been demonstrated at high
PRF (100MHz) in a linearly-polarized output beam.
Spectral Beam Combination (SBC) of multiple fiber laser outputs has been shown to be an effective way to scale the
power of fiber laser systems while maintaining
near-diffraction-limited beam quality. The fiber SBC system maintains
many of the key advantages of individual fiber lasers, such as high efficiency, excellent beam quality independent of
output power and relaxed thermal management requirements. Several approaches to spectral beam combination have
been demonstrated including single grating in linear oscillator, single grating in master oscillator power amplifier
(MOPA), dual grating MOPA and dual grating ring oscillator configurations. Each of these variations has certain
advantages in terms of the system design and fiber laser requirements. In this paper we analyze the different approaches
and compare them in terms of combined beam quality, line-width requirements of the individual fiber laser channels,
power scalability and system complexity. The results obtained using the different SBC approaches at Aculight are summarized in the context of this analysis.
We describe a three-channel, spectrally beam combined (SBC), 1-&mgr;m fiber laser that features a SBC power combining
efficiency of 93%, versatile master-oscillator, power-amplifier (MOPA) fiber channels with up to 260 W of narrowband,
polarized, and near-diffraction limited output, and currently produces 522 W of average power with a dispersed (non-dispersed)
beam quality at 522 W of 1.18x (1.22x) diffraction limited. To our knowledge, these results represent the best combination of output power and beam quality achieved by SBC to date.
We describe a three-channel, spectrally beam combined (SBC), 1-&mgr;m fiber laser that features a SBC power
combining efficiency of 93%, versatile master-oscillator, power-amplifier (MOPA) fiber channels with up to 260 W
of narrowband, polarized, and near-diffraction limited output, and currently produces 522 W of average power with
a dispersed (non-dispersed) beam quality at 522 W of 1.18x (1.22x) diffraction limited. To our knowledge, these
results represent the best combination of output power and beam quality achieved by SBC to date.
We report on progress toward power scaling Yb fiber lasers beyond kW levels by an efficient and versatile architecture that maintains near diffraction limited beam quality. For this work, power scaling is performed at two distinct levels. The first utilizes a diffraction grating to spectrally beam combine (SBC) the output from several master-oscillator, poweramplifier (MOPA) fiber lasers with a goal of producing high quality combined beams with > 1 kW of power. The second involves scaling individual MOPA outputs to > 200 W, thereby reducing the number of lasers required for SBC. As a first step toward reaching these goals, we have developed Yb fiber MOPAs producing up to 208 W of polarized, narrow band, and near diffraction limited output and have demonstrated two-channel fiber laser SBC with a power combining efficiency of 93%, a combined beam power of 258 W, and a dispersed axis M2 of 1.06. These results represent a significant advance in high brightness, spectrally beam combined laser systems.
The materials and process technology necessary to fabricate free- standing, circularly-polarizing thin films based on chiral polymer liquid crystalline materials has recently been demonstrated. Free-standing membranes with thicknesses on the order of 10 microns and diameters in excess of 7 cm have been fabricated. The spectrally selective films possess exceptional optical and mechanical properties, exhibiting polarization contrast in excess of 250 with out-of-band transmission greater than 95%. The theory and performance of these filters are presented with specific attention given to the predicted effects of space environments on the durability of this materials technology. Environmental effects to be discussed include wide temperature cycling, radiation and atomic oxygen scavenging.
Glass-forming liquid crystals (GLC) are a new class of materials suitable for use in a wide variety of latching optical and photonic applications. Applications range from physically small devices for latching fiber optic devices, such as switches and attenuators, to physically large devices, such as corrective optics for deployable space-based optical systems. Previously, we demonstrated the ability to electronically change and then latch the birefringent characteristics of an optical device. Recent data indicates that not only does the chemical design of a GLC material impact the electro-optic properties of a latching device, but stereochemistry also plays a significant role. This paper presents static and dynamic optical data taken on a set of four similar GLC materials. Based on the results of this study, we have developed a qualitative understanding of the structure-property relationships, leading to GLC materials that are suitable for use in latching electro-optic devices.
This paper presents the current status of alignment techniques for a new class of liquid crystalline material being developed for both passive optical filtering/polarizing and latching electro-optic applications. This new glassy liquid crystal (GLC) material has the unique property of being electro-optic and fully latching. That is, in one state, the material has the properties of a conventional nematic liquid crystal, capable of being aligned with either an electric or magnetic field; while in its other state, it is an optical quality solid that maintains the molecular alignment set while in the fluid state. Molecular alignment of nematic GLC films is a critical technology necessary to develop high-performance, novel latching devices. The alignment of the nematic pendant component of GLCs directly correlates to the optical contrast, switching speed (turn-on time), and decay speed (turn-off time) of an active latching device. There has been little prior research conducted to assess conventional LC alignment techniques for use with GLCs. The processing and effectiveness of multiple alignment techniques will be discussed.
The materials and process technology necessary to fabricate free-standing, circularly-polarizing thin films based on chiral polymer liquid crystalline materials has recently been demonstrated. Free-standing membranes with thicknesses on the order of 10 microns and diameters in excess of 7 cm have been fabricated. The spectrally selective films possess exceptional optical and mechanical properties, exhibiting polarization contrast in excess of 250 with out-of-band transmissions greater than 95%. The theory, materials, processing techniques and spectral performance of these filters are presented.
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