Solder Jetting is a versatile assembly and packaging technology for hybrid photonics and MEMS. The jetting device for liquid solder droplets ranging from 100 μm to 760 μm in diameter is manipulated in up to 6DOF independently from the complex assembly environment, thus able to reach even complex and 3D-shaped joining geometries. Creating the joint between the component and the system platform the metallic solder alloy is advantageous over standard adhesives due to better temperature, radiation and long term stability, making it favourable e.g. for high power photonics applications and also serving for electrical and thermal conductivity. In various photonics applications alignment stability up to 1.5±0.5 μm have been demonstrated.

The correction of surface shape errors is not only essential to optical systems, but becomes more and more important for optical metrology. We present a deformable mirror, which is suitable for the correction of astigmatism up to an amplitude of +/- 10 mu m. The mirror substrate is exchangable, allowing for an easy adaptation to different spectral ranges. The design of the deformable mirror enables stable astigmatism amplitudes over several days according to the set-and-forget principle. A finite element analysis is performed to simulate the surface deformation, which is compared to measurements of a prototype. The adjustment accuracy is proven by repeatedly exchanging of two substrates and performing interferometric measurements of the deformation. Experimental measurements with the first prototype demonstrate a very high long-term stability. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We report on an opto-mechanical metal mirror design for highly dynamic, diffraction-limited focus shifting. Here, the mechanical geometry of the membrane is of crucial interest as it must provide sufficient optical performance to allow for diffraction limited focussing and have a high mechanical eigenfrequency to provide dynamic motions. The approach is the analytical consideration of the plate theory and provides the basis for a parameterized finite element model. By means of an finite element analysis (FEA), essential steps for the optimization of the mirror design with respect to a wide range of optical power and a high operating frequency are shown. To verify the results of the FE analysis, the deformed surface is decomposed into Zernike coefficients. An analysis of the point spread function is performed to evaluate the optical performance. For dynamic evaluation a modal and a harmonic vibration analysis are conducted. The opto-mechanical design allows a biconical deformation of the mirror surface, enabling the generation of a diffraction-limited spot diameter in the adjustment range of ±1.2 dpt. The surface shape error in this range is 53 nm. The dynamic analysis shows the first excited eigenfrequency at 21.6 kHz and a diffraction-limited operation frequency at 9.5 kHz. This paper provides an alternative design approach for highly dynamic beam oscillation in the Z direction, forming a complement to highly dynamic X-Y scanning systems.

Anti-Stokes fluorescence cooling of a Yb-doped silica glass optical fiber preform is achieved using a high-power laser in a double-pass configuration. The coherent laser beam illuminates the silica glass preform in the red tail of its absorption spectrum, and the heat is carried out by anti-Stokes fluorescence of the blue-shifted photons. The high-purity Yb-doped silica glass preform has low parasitic absorption and is codoped with modifiers to mitigate the quenching-induced non-radiative decay for sufficiently high concentrations of Yb ions in silica glass. Therefore, sufficiently large laser absorption could be achieved to observe cooling while maintaining a near-unity external quantum efficiency.

This paper describes an opto-mechanical concept of a deformable metal mirror membrane, which can shift the focus position over a large range by use of a single actuator. The core element of the mirror is a diamond turned tulip-shaped membrane, the design is optimized to correct astigmatic aberrations which arise from the use of a curved mirror under a deflection angle. For this purpose, the target mirror surface is biconic. The manufactured mirror was tested with a maximum central deflection of 28 µm and, when used in combination with a 200 mm focal lens, is capable of producing a focus shift of up to 17.9 mm with a resulting wavefront aberration of 238.7 nm RMSerror.

We report nearly an order of magnitude improvement over the lowest temperature achieved in laser-cooling of Yb-doped silica glass. The 6K cooling relative to the ambient temperature was achieved by pumping the sample at 1035nm.

Laser cooling of a solid is achieved when a coherent laser illuminates the material, and the heat is extracted by annihilation of phonons resulting in anti-Stokes fluorescence. Over the past year, net solid-state laser cooling was successfully demonstrated for the first time in Yb-doped silica glass in both bulk samples and fibers. Here, we report more than 6 K of cooling below the ambient temperature, which is the lowest temperature achieved in solid-state laser cooling of silica glass to date to the best of our knowledge. We present details on the experiment performed using a 20 W laser operating at a 1035 nm wavelength and temperature measurements using both a thermal camera and the differential luminescence thermometry technique.

In this contribution, we report high-power Raman frequency downconversion based on an Yb-doped fiber amplifier and a linear external diamond Raman cavity. A maximum output power of 136 W with nearly diffraction-limited beam quality was achieved by pumping in quasi-continuous-wave mode with 10% duty cycle and 10 ms on-time duration. For continuous-wave operation, we achieved record average power of 46 W centered at 1178 nm. The emergence of stimulated Brillouin scattering in diamond is further investigated. This technology shows the potential to extend the spectral range of fiber lasers to reach uncommon wavelengths at high power levels.

Supported by both experimental and simulated results, this contribution demonstrates the heat load distribution in a copumped, ytterbium (Yb)-doped fiber amplifier seeded with two different wavelengths can be significantly changed depending on the seed power ratio. Longitudinal temperature measurements in a Yb-doped 10.5 m 20/400 mu m fiber confirm a significant shift of the heat load maximum by 3.5 m towards the fiber output when decreasing the seed power ratio from P-1030nm/P-1080nm = 1.7 to 20. In single-tone operation with a seed power of P-1080nm = 3.5 W, the amplifier is limited by the onset of transverse mode instabilities at a power-level of 1950 W. However, dual-tone seeding with a seed power ratio up to P-1030nm/P-1080nm = 10 reduces the TMI- threshold dramatically down to 1050 W. Additionally we show, that the modal instability threshold is very susceptible to 1030 nm seed noise in the frequency regime up to 10 kHz.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

We report the observation of anti-Stokes fluorescence cooling of Yb-doped silica glass by 0.7 degrees Celsius. We conduct a detailed investigation of the cooling parameters of this glass, including the wavelength dependence of the cooling efficiency as a function of the wavelength and also the parasitic absorption of the pump laser. The measurements are performed on three different glass samples with different compositions and cooling is observed in all samples to varying degrees. The results highlight the possibility of using Yb-doped silica glass for radiation-balancing in fibers. Radiation-Balancing is a viable technique for heat mitigation in lasers and amplifiers.

A laser based soldering technique - Solderjet Bumping - using liquid solder droplets in a flux-free process with localized thermal impact demonstrates the all inorganic, adhesive free attachment of optical components and support structures made of heterogeneous materials for a high-resolution optical filter under harsh environmental conditions. Space applications demand an attachment technology which maintains the precise alignment of bonded components and overcomes challenges of common adhesives such as being more radiation resistant and appropriate for vacuum environments. Besides, stress and strain induced into optical components can deteriorate the wavefront of passing light and therefore reduce the system performance significantly. The presented case study shows the mandatory changes in the design of an optical filter instrument according to the boundary conditions of Solderjet Bumping for different bonding issues. First, a filter window made of N-BK10, covering the optical sensor beneath, is soldered into a frame of DilverP1 (R). Second, this sub-assembly is aligned w.r.t. to fiducials on a support structure and is attached in this state by soldering as well. The process chain of Solderjet Bumping including cleaning, wettable metallization layer, handling, soldering and inspection is discussed. This multi-material approach requires well-defined reflow energies to melt the spherical shaped solder preforms to create a media-fit joint and to prevent damages on the fragile filter window simultaneously. The findings of process parametrization and environmental testing are presented. The optical performance with respect to stress/strain before and after soldering as well as the alignment state are evaluated using non-contact optical techniques.

The measured fiber coupling efficiency (FCE) in atmospheric laser communication is not fully explored. We experimentally study the FCE for tip-tilt aberrations. Finally, we explain the FCE with the tip-tilt phase response.

Nonlinear effects and transverse mode instabilities (TMI) limit power scaling of single-mode fiber lasers. To overcome these limitations not only the fiber design but also laser relevant properties of the actively doped material itself need to be optimized. By being able to fabricate Yb-doped fibers for high power applications in-house, we have direct access to laser relevant material parameters. We fabricated fibers using three different co-doping systems, namely Yb:Al:P, Yb:Al:F, and Yb:Al:F:Ce. Afterwards we characterized and compared their laser relevant properties. All three co-doping systems showed nearly identical background losses and absorption cross-sections. In contrast, we found that the PD losses and the factor between PD losses @633nm and the laser wavelength range (1 mu m) to be significantly different. The retrieved characterization results were implemented into our simulations tool in order to improve the reliability of predictions. Finally, we characterized the fibers in kW-amplifier setups according to their power scaling limits, especially the TMI threshold. This cycle of fiber fabrication, characterization, and simulation enabled us to identify the impact of individual fiber parameters on the TMI threshold. We demonstrated that the impact of PD loss leads to a reductions of the TMI threshold for Yb:Al:F co-doping system of 13% to 23% (depending on the Yb-concentration). The PD loss for the two other systems was proved to be significantly lower and was found to have no impact on the TMI threshold. We experimentally proved that your in-house Yb:Al:P and Yb:Al:F:Ce fibers performed like PD-free fibers.

Currently, the achievable average power from single-mode Yb-doped fiber lasers is in the multi-kW range [1]. However, the transmission range or the spectral gain of the active medium often limits the output power of highly demanded laser sources at uncommon wavelengths. Nonlinear frequency conversion represents a versatile approach to extend the spectral range at high power levels and is thus beneficial for wavelength-dependent applications. Compared to optical parametric oscillators (OPOs) the Raman laser technology is less complex and does not require management of phase matching. Furthermore, the spatial-hole-burning-free characteristic of the Raman gain provides an advantage for narrow band, high power operation [2]. Industrial CVD-diamond is an attractive medium for Raman frequency conversion and especially suitable for high power regions due to its unique combination of thermal and optical properties [3]. Using a second-Stokes setup lowers the threshold and increases the obtainable wavelength shift ever further [4]. Here, we employ this technology to achieve record power at 1478 nm in cw-operation.

Adaptive optical pre-compensation is seen as crucial for free-space laser communication in order to overcome the influence of atmospheric turbulence, particularly with respect to Earth-to-GEO feederlinks. This paper presents an experimental investigation into adaptive optical pre-compensation under large point-ahead-angles. We detail the design and realization of a free-space laser communication experiment over a 1.0 km horizontal path using a divergent beacon beam and a focussed signal beam, propagating in opposite directions. We describe the design and development of our experimental setup and measurement campaign using real turbulence. The median isoplanatic angle was calculated to be 0.16 mrad, while an increase in the received optical power through pre-compensation could be demonstrated for point-ahead-angles in the range of 0.13 mrad to 0.27 mrad.

In this contribution the influence of fabrication technique (solution doping, gas-phase doping) and the choice of suitable material systems (Al, P, Yb:SiO2 and Al, F, Yb:SiO2) for high power fiber laser materials on their optical properties is analyzed. The materials under analysis contain low amounts of codopants (Yb < 0.15 mol%, other <1.2 mol%). The effects on refractive index, attenuation, absorption and emission cross section as well as on photodarkening are addressed. The main part concerns with the analysis of photodarkening, in fact the evolution of individual defect centers are spectrally and temporally investigated by means of 2D curve fitting. It is suggested that this spectro-temporal fitting procedure can lead to new insights in the development of photodarkening on a level of the defects themselves.

Fiber lasers entered numerous applications due to their high efficiency and superior stability. Particularly in space, those lasers have to fulfill additional requirements set by the harsh environment, typically characterized by large temperature gradients, vibration and shock as well as different kinds of radiation. In this contribution, we will report on the development and realization of a fiber laser intended to operate as part of a Rendezvous and Docking 3D-Lidar system considering the aforementioned specialties. Power scaling of pulsed as well as continuous-wave fiber lasers is yet another way to exploit new application fields in space.

We present highly efficient three-channel dual-grating spectral beam combining with a combined signal output power of 5.5 kW at an excellent beam quality of M2 = 1.5. Three 2-kW all-fiber narrow-linewidth continuous-wave Ytterbium-doped fiber amplifiers at 1050 nm, 1070 nm and 1090 nm were combined using in-house fabricated polarizationindependent dielectric reflection gratings. The total combining efficiency was 94% at full power level, which is close to the expected value referred to the incorporated grating’s efficiency in a dual-grating setup.

We present the amplification of a narrow-bandwidth signal at a wavelength of 1018 nm to a power exceeding 600 W with a stable output polarization state. The beam showed an excellent, nearly diffraction-limited beam quality. The high-power output could be realized using an in-house designed and fabricated fiber with a core-cladding diameter ratio of 32/260, ultra-low NA of 0.041, and ring-up doping. A seed source with high amplified spontaneous emission (ASE) suppression was also required, which was realized by a double-pass pre-amplifier with 13 W output power. (C) 2019 Optical Society of America