Entwicklung von miniaturisierten Fourier-Transformations-Spektrometern und ihre Herstellung mit dem LIGA-Verfahren

Abstract

In this work miniaturised Fourier Transformation Spectrometers have been developed. They are based on LIGA technology and designed for mobile applications in the near infrared spectrum. First a short overview about different concepts for miniaturised near infrared spectrometers is given. Then the theory needed for the design of Fourier Transformation Spectrometers is discussed in detail. Following the chapter about the theoretical basics, two concepts of miniaturised Fourier Transformation Spectrometers are introduced. Both spectrometers are basically Michelson Interferometers which consist of a micro-optical bench with an integrated actuator. The optical benches and actuator are produced with LIGA technology. The spectrometers are very compact. All required components are placed on a 10 x 10 mm 2 substrate. The needed optical and electronic components such as lenses, beam splitters and diodes are assembled into the optical bench. The components are positioned by alignment structures. Due to the precision of the LIGA produced alignment structures there is no need for an active alignment. Two concepts were investigated for the actuators. One a novel piezo based inchworm actuator. The second an electromagnetic actuator. The design of the optical benches and both actuator types are described in detail. Special emphasis is placed on the description of the electromagnetic actuator. The different analytical and numerical models used to design the actuator are presented. Also manufacturability considerations of the LIGA components are addressed. The design rules used are explained in detail. Both systems manufacturing methods are presented. Emphasis is placed on the manufacturing steps which had to be modified or developed for spectrometer manufacturing. The prototype manufacturing was carried out using synchrotron radiation, a process which is called direct LIGA. A low cost manufacturing method using replication techniques was investigated. For this a mold insert was manufactured for the system with the electromagnetic actuator. Initial nickel iron structures made through replication and subsequent electroplating are presented. The functionality of the spectrometers was demonstrated. Spectra could be recorded for laser and with white light sources. The best resolution achieved was 24,5 nm. The optical resolution is currently limited by the maximum optical path difference achieved with the integrated actuator. The maximum usable travel of the actuator was 60 μm. For larger travels the actuator showed an unwanted switching behaviour. The performance of the actuator was tested and an analytical model for the switching behaviour was established. Measurements show good agreement between the model and experimental data.