Thermomechanical design, hybrid fabrication, and testing of a MOEMS deformable mirror

Abstract

Abstract. This paper reports on the thermomechanical modeling and characterization of a micro-opto-electro-mechanical systems deformable mirror (DM). This unimorph DM offers a low-temperature cofired ceramic substrate with screen-printed piezoceramic actuators on its rear surface and a machined copper layer on its front surface. We present the DM setup, thermomechanical modeling, and hybrid fabrication. The setup of the DM is transferred into a thermomechanical model in ANSYS Multiphysics. The thermomechanical modeling of the DM evaluates and optimizes the mount material and the copper-layer thickness for the loading cases: homogeneous thermal loading and laser-loading of the mirror. Subsequently, the developed and theoretically optimized DM setup is experimentally validated. The homogeneous loading of the optimized design results in a membrane deformation with a rate of −0.2 μm K −1 , whereas the laser loading causes an opposed change with a rate of −0.2 μm W −1 . Therefore, the proposed mirror design is suitable to precompensate laser-generated mirror deformations by homogeneous thermal loading (heating). We experimentally show that a 35-K preheating of the mirror assembly compensates for an absorbed laser power of 1.25 W. Therefore, the novel compensation regime "compound loading" for the suppression of laser-induced deformations is developed and proven.

Performance of a thermal-piezoelectric deformable mirror under 62 kW continuous-wave operation

“…The metallic mirror mount is attached to a Peltier element for temperature control of the mirror assembly. For more details see [11].…”

“…A finite element analysis and a first proof of principle are shown in [11] and [17]. In the previous work, however, the limits of the compensation method were not analyzed; for example, limits which might occur due to an increase in temperature.…”

“…Other research has focused on actuator patterns [8,9] and material considerations [10]. Nevertheless, these types of deformable mirrors suffer from thermal lensing, as discussed in [11], limiting their application, especially in case of long-term, high-power continuous-wave (CW) operation. The absorption of laser radiation can deform the mirror surface, and the piezoelectric stroke is sometimes not sufficient to compensate for the laser systems thermal lensing.…”

“…A thermal-piezoelectric deformable mirror (TPDM) combines the advantages of large amplitude bi-material thermal activation and fast piezoelectric activation with moderate amplitudes [11,18]. Here, the thermal activation is generated by mount heating to generate the mirror deformation by the bi-material effect.…”