This work presents the design and characterization of an approach for areal surface profilometry with sub-nm axial resolution. The developed approach is based on a low-coherence interferometer enhanced by an dispersive element to control the axial resolution and measurement range. Optical path differences are detected by an imaging spectrometer where equalization wavelengths are determined as a basis for fitting spectra. This enables the acquisition of surface profiles with a length of up to 1.5 mm without mechanical scanning where a minimal resolution of 0.1 nm in an axial measurement range of nearly 80 µm was achieved. The resolution calculation was based on the standard deviation of measured feature heights. In addition to the system design, its capabilities are demonstrated on samples such as height standards.

Within this work a scan-free, low-coherence interferometry approach for surface profilometry with nm-precision is presented. The basic setup consist of a Michelson-type interferometer which is powered by a super-continuum light-source (Δλ= 400-1700 nm). The introduction of an element with known dispersion delivers a controlled phase variation which can be detected in the spectral domain and used to reconstruct height differences on a sample. In order to enable scan-free measurements, the interference signal is spectrally decomposed with a grating and imaged onto a two-dimensional detector. One dimension of this detector records spectral, and therefore height information, while the other dimension stores the spatial position of the corresponding height values. In experiments on a height standard, it could be shown that the setup is capable of recording multiple height steps of 101 nm over a range of 500 m with an accuracy of about 11.5 nm. Further experiments on conductive paths of a micro-electro-mechanical systems (MEMS) pressure sensor demonstrated that the approach is also suitable to precisely characterize nanometer-sized structures on production-relevant components. The main advantage of the proposed measurement approach is the possibility to collect precise height information over a line on a surface without the need for scanning. This feature makes it interesting for a production-accompanying metrology

Fiber lasers are a fast growing class of lasers due to their reliability, efficiency and flexibility. This has made fiber lasers a versatile tool for manufacturing, sensing and healthcare, not forgetting the contribution of Erbium-doped amplifiers to optical communications. Yet available wavelengths by direct emission are quite restricted to the visible and near infrared wavelength interval (500 nm to 2 micron), with very few offering high power and efficient operation, namely 1 micron, 1.5 micron and 2 micron wavelengths. In this paper we comment on the state of the art and future challenges in the field of fiber lasers to address new wavelength and new applications. In particular to extended the emission interval above 3 micron. This work collects the experience of the COST MP1401 Network on fiber lasers and their application and will present some of the areas were efforts have been focused. More exhaustive material will be presented at the conference.

Within this work an alternative approach to precision surface profilometry based on a low-coherence interferometer is presented. Special emphasis is placed on the characterization of edge effects, which influence the measurement result on sharp edges and steep slopes. In contrast to other works, this examination focuses on the comparison of very broadband light sources such as a supercontinuum white-light source (SC; 380 - 1100 nm) and a laser-driven plasma light source (LDP; 200 - 1100 nm) and their influence on the formation of these effects. The interferometer is equipped with one of these broadband light sources and a defined dispersion over a given spectral range. The spectral width of the light sources in combination with the dispersive element defines the possible measurement range and resolution. Instead of detecting the signals only in a one-dimensional manner, an imaging spectrometer on the basis of a high resolution CMOS-camera is set-up. Through the introduction of a defined dispersion, a controlled phase variation in the spectral domain is created. This phase variation is dependent on the optical path difference between both arms and can therefore be used as a measure for the height of a structure which is present in one arm. The results of measurements on a 100 nm height standard with both selected light sources have been compared. Under consideration of the coherence length of both light sources of 1.58 μm for the SC source and 1.81 m for the LDP source differences could be recorded. Especially at sharp edges, the LDP light source could record height changes with slopes twice as steep as the SC source. Furthermore, it became obvious, that measurements with the SC source tend to show edge effects like batwings due to diffraction. Additional effects on the measured roughness and the flatness of the profile were investigated and discussed.

Broadband light sources provide a significant benefit for optical coherence tomography (OCT) imaging concerning the axial resolution. Light sources with bandwidths over 200 nm result in an axial resolution up to 2 microns. Such broad band OCT imaging can be achieved utilizing super continuum (SC) light sources. The main important disadvantage of commercial SC light sources is the overall size and the high costs. Therefore, the use of SC light sources in small OCT setups and applications is limited. We present a new small housing and costeffective light source, which is suitable for OCT imaging. The used light source has dimensions of 110 x 160 x 60 mm and covers a wavelength range from 390 nm up to 2500 nm. The light source was coupled in a dual band OCT system. The light is guided into the interferometer and split in reference and sample beam. The superimposed signal is guided to the spectrometer unit, which consists of two spectrometers. This spectrometer system separates the light. One band centered at 800 nm with a full bandwidth of 176 nm and a second band centered at 1250 nm with a full spectral width of 300 nm was extracted. The 800 nm interference signal is detected by a silicon line scan camera and the 1250 nm signal by an indium gallium arsenide linear image sensor. In this test measurement a plastic foil was used as a sample, which is composed of several plastic film layers. Three dimensional images were acquired simultaneous with the dual band OCT setup. The images were acquired at an A-scan rate of 1 kHz. The 1 kHz A-line rate was chosen because so far the optical power of the light source is not optimal for high speed OCT imaging. The source provides 2 mW in the range of 390 nm to 800 nm and 25 mW in the range from 390 nm to 1650 nm. Furthermore, we coupled the light source by a 50:50 optical fiber coupler, which also reduces the overall optical power of the light source within the OCT setup. Nevertheless, we demonstrated that this new small-package and cost-effective light source is very suitable to carry out OCT imaging. The use of this light source can open up new OCT applications, which require OCT setups with very high axial resolution and small footprint.

Manufacturing of precise structures in MEMS, semiconductors, optics and other fields requires high standards in manufacturing and quality control. Appropriate surface topography measurement technologies should therefore deliver nm accuracy in the axial dimension under typical industrial conditions. This work shows the characterization of a dispersion-encoded low-coherence interferometer for the purpose of fast and robust surface topography measurements. The key component of the interferometer is an element with known dispersion. This dispersive element delivers a controlled phase variation in relation to the surface height variation which can be detected in the spectral domain. A laboratory setup equipped with a broadband light source (200 - 1100 nm) was established. Experiments have been carried out on a silicon-based standard with height steps of 100 nm under different thermal conditions such as 293.15 K and 303.15 K. Additionally, the stability of the setup was studied over periods of 5 hours (with constant temperature) and 15 hours (with linear increasing temperature). The analyzed data showed that a height measurement of 97:99 +/- 4:9nm for 293.15 K and of 101:43 +/- 3:3nm for 303.15 K was possible. The time-resolved measurements revealed that the developed setup is highly stable against small thermal fluctuations and shows a linear behaviour under increasing thermal load. Calibration data for the mathmatical corrections under different thermal conditions was obtained.