C. Bruchmann

Thermo-mechanical properties of a deformable mirror with screen printed actuator

This paper reports on the thermo-mechanical modeling and characterization of a screen printed deformable mirror. The unimorph mirror offers a ceramic LTCC substrate with screen printed PZT layers on its rear surface and a machined copper layer on its front surface. We present the thermo-mechanical model of the deformable mirror based on Ansys multiphysics. The developed mirror design is practically characterized. The homogeneous loading of the optimized design results in a membrane deformation with a rate of -0.2 μm/K, while a laser loading causes a change with a rate of 1.3 μm/W. The proposed mirror design is also suitable to pre-compensate laser generated mirror deformations by homogeneous thermal loading (heating). We experimentally show that a 35 K pre-heating of the mirror assembly could compensate an absorbed laser power of 1.25 W.

Novel construction of a deformable mirror for laser beam shaping

This paper reports on a novel construction of a deformable mirror for laser beam shaping. The deformable mirror is actuated by screen-printed thick film piezoceramic unimorphs based on lead zirconate titanate (PZT). Different actuator layouts are realized and will be presented. We use Low Temperature Cofired Ceramics (LTCC) as a substrate material with a metallization as reflective surface. LTCC offers easy integration of holding structures. The reflective mirror surface is electroplated copper. After deposition, the copper layer is diamond machined to achieve excellent optical surface quality <10 nm (rms). We build deformable mirrors with 1, 13 and 19 actuators and a total stroke of more than 20 μm and characterize them with a wave front sensor.

Application of PZT thick-films on adjusting purposes in micro-optical systems

A PZT thick-film is printed on an Al2O3-Substrate, generating a cantilever monomorph. A task of positioning with two degrees of freedom is successfully fulfilled. It is realized by two parallel arranged cantilevers that are mechanically combined with a bar with solid hinges. The solid hinges allow flexibility for different amounts of bending of the two cantilevers, while the bar permits a stiff support for a lens. As the bar underlies very small torsion there is no stress induced change in the index of refraction of the lens. Different combinations of hinges are simulated and practically tested. In the presented work, a lens is successfully positioned in front of a laser diode. The loss of the coupling efficiency due to the shrinking of the adhesive joint can be scaled down. The paper presents the theoretical work including the report on analytic and FEM simulation of both deflection and stress. The practical validation is also presented. A simple sensor system is used to find an optimized position of the lens in front of the diode. This position is automatically held over a long period of time. With the fabrication of the actuator using thick-film printing and laser cutting a low cost device is built.

First results on electrostatic polymer actuators based on UV replication

The miniaturization of actuators results in two major consequences: First, the reduction in efficiency depending on the physical principle. Second, the increasing requirements in positioning accuracy during the assembly and fabrication process in combination with low cost production. Electrostatic polymeric actuators providing out-of-plane motion which can be completely fabricated in parallel fabrication steps and hence be produced on wafer level are compliant to these tolerance and cost constraints. The electrostatic actuation principle is a surface effect and therefore independent of the volume. In addition, the efficiency of electrostatic actuation increases with a decreasing gap size between the electrodes. The simple morphology of such actuators can be easily produced by UV-replication of polymeric materials. In consequence, the electrostatic actuation principle is predestined for the combination with low cost wafer level fabrication. This paper reports on the first results of successfully fabricated electrostatic actuators produced on wafer level. Instead of using a standard silicon substrate our approach is based on the lithographic structuring of the non-conducting material ORMOCER®. In comparison ORMOCER® has a significantly lower elastic modulus (about 1 GPa). Therefore, only a fraction of actuation voltage is necessary for a similar deflection. The material is structured using photolithography and the electrodes are realized with coatings of thin metal layers. Experimental results show a deflection up to 49,1 μm at 500 V for an 75 μm thick cantilever beam fixed at both ends. Good agreement between measurements and simulations is achieved, proving the applicability of the software and the assumed material parameters.

New results of unimorph laser mirrors with screen printed actuator

This paper reports on new results of the development of a unimorph laser beam shaping mirror based on Low Temperature Cofired Ceramics (LTCC). The deformable mirror is actuated by a side screen printed piezoceramic thick film based on lead zirconate titanate (PZT). The reflective surface is electroplated copper that is diamond machined to flatten the surface. We introduce the solder jet bumbing fixation technology to mount the deformable mirror into a metallic mounting. This assembling technology introduces very little energy input and thus also very little deformation into the mirror. The material of the mounting is CE7 that is especially thermal adapted to the deformable mirror. We will present results on deflection and resonance frequency for two different mirror designs.

60-fs Pulses with 1 µJ Pulse Energy Generated by Nonlinear Compression of a Short-Pulse Fiber Laser

We report on the fiber laser based generation of 45 W average power of 60-fs pulses using nonlinear spectral broadening in a large-mode-area photonic crystal fiber followed by compression with chirped mirrors.