Anti-resonant hollow core fibers (AR-HCF) have been investigated for several use cases relating to high power transmission. Single mode, low-loss operation is needed in high-speed telecommunications and in high-energy beam delivery applications. In these fibers, higher order modes leak out of the core through the surrounding capillaries and subsequently are highly attenuated upon propagation resulting in effective mode filtering. With regards to CW operation, 900W have been delivered through a single resonant ring AR-HCF, and 1kW through a nested AR-HCF. This study presents an experimentally derived performance comparison of the spatial, spectral, and loss metrics between these two types of fibers when using an identical 1kW laser source.

We present an investigation of birefringence in ultrashort pulse and phase mask written fiber Bragg gratings (FBGs). Polarization dependent loss and shift of the resonance wavelength as well as the polarization extinction ratio of the FBGs was determined. As expected, we could find a significant dependency connecting the grating strengths and the birefringence . For high reflector gratings, birefringence of up to 10^-5, corresponding to a resonance wavelength shift of up to 10 pm was measured. The results show excellent suitability for usage of the FBGs in linear polarized fiber lasers.

We present a novel technique for the control of the spectral profiles of fiber Bragg gratings written with ultrashort laser pulses and the phase mask technique. Instead of controlling the modification strength along the grating, the apodisation is realized by controlling the cross-sectional overlap of modification and fiber core by a custom designed shaping aperture. As a proof of concept, gratings were realized with super-Gaussian shaped profiles with different orders, producing the expected spectral profiles, which was verified by simulations.

In this paper, we present the results of development of a 200 W laser systems capable to deliver narrowband (10 GHz) radiation with tunable wavelength (350-400 pm) and tunable linewidth (10-50 GHz). The compact design, capability of simultaneous emission of several narrowband emission lines (e.g. for Rb/Cs or Rb/K gas systems), high signal to noise ratio (>30 dB) makes the new system suitable for SEOP and other ultra-narrow linewidth demanding applications.

Q-switched Nd-based lasers are used for a variety of medical and manufacturing applications and require extremely high efficiency and stability from the diode pump, but limited commercially available solutions exist for single spatial mode direct pumping of Nd-based lasers at 885 nm. To satisfy this need, Freedom Photonics has developed ultra-robust watt-class diffraction-limited 885 nm diode lasers. We are in the process of performing full reliability and lifetime assessments on our watt-class single-mode 885 nm diode lasers. To achieve high reliability, we employ facet passivation methods to protect against catastrophic optical mirror damage (COMD). Additionally, progress on the development of VBG-locked packages will be discussed. These devices may be used as reliable, high efficiency pumps for Nd-doped solid-state lasers.

Holographic elements embedded in a photo-thermo-refractive (PTR) glass were recently deployed in a wide variety of applications. This material allowed recording of phase Bragg gratings with high efficiency for visible and near IR spectral regions. Recent advances in technology enabled fabrication of a large variety of elements ideally suitable for quantum optics applications such as single photon detection, atomic clocks, quantum computing and network. PTR glass based diffractive elements are used as combiners, signal separation, pump suppression and as dispersive elements. High efficiency, narrow bandwidth, high suppression, and large dispersion are key parameters that made those elements irreplaceable.

We report on the first inscription of chirped VBG in fused silica for high power applications such as CPA systems. The cVBG are inscribed into bulk fused silica using ultrashort laser pulses and the phase mask scanning technique. The influence of inscription parameters on the grating properties as well as the dispersion characteristics of the cVBG are investigated. Further steps towards scaling the dimensions of the fs-written cVBG towards applications inside CPA systems are discussed.

The sizable footprint of a volume Bragg grating (VBG) allows access to a three-dimensional structure upon which local Bragg elements within the grating volume can be collectively engineered. In this work, a set of π phase-shifts is distributed across the structure of a longitudinally chirped VBG. For each locality on the grating facet, either a single or multiple phase-shifts can be embedded at various positions along its thickness, transforming the element into a transversely phase-shifted, longitudinally chirped VBG. The versatile platform of such an element provides spectral tunability to the otherwise single-wavelength operation found in fiber Bragg gratings or alike.

The spectral beam combining for narrowband laser beams with spectral width below 1 nm by using of Transmitting Bragg Gratings (TBGs) has already shown high efficiency and high quality of a combined beam. For high power lasers emitting broadband beams with spectral width exceeding 1 nm, it is necessary to consider effect of TBGs spectral dispersion on divergence of a combined beam. In this work, the interaction of polychromatic radiation with TBGs was simulated by the Floquet approach. The scheme for spectral dispersion compensation of broadband beam is described.

We report on the optimization of ultrashort pulse laser written VBGs for UV applications. The VBGs are directly inscribed in fused silica by applying ultrashort laser pulses and the phase mask scanning technique and exhibit geometries and reflectivities comparable to conventional gratings. For applications below 300nm, absorption in the VBG is a critical issue. Therefore, we investigate the influence of absorption on writing parameters and thermal annealing. The optimized gratings in fused silica show a significantly reduced residual absorption, making these optimized gratings well suited for low wavelength applications especially in the Near-UV and below.