Applications of spectroscopy with multiwavelength sources

Applications of spectroscopy with multiwavelength sources

Hänsel, A. (TU Delft ImPhys/Optics)

Urbach, Paul (promotor)
Bhattacharya, N. (copromotor)

Delft University of Technology

2018-06-04

Spectroscopy is a powerful tool to investigate the physical properties of complex systems. The interaction of light with matter allows to get insights into the structure of it. Chapter 1 is dedicated to introduce this topic and to show the developments of the technologies that paved the way to its success. Special focus is given to the techniques that are used in this work. This includes monolithically integrated tunable laser sources, as well as integrated mode locked lasers. In Chapter 2 we guide through the design process of single mode laser source using the generic approach and exploiting the availabilty of multi-project wafers. The design of a Fabry-Perot laser along with its benefits, drawbacks and the underlying physical concepts will be demonstrated. This requires theoretical background in solid state physics; the necessary basics are given in the text. Chapter 3 makes use of this background and expand the design to ring lasers. Chapter 3 also illustrates characterisation techniques for such laser sources. The presented device is investigated regarding its capabilities for gas spectroscopy. To reach different absorption lines that enable spectroscopy for different gas species, the laser design has been adapted for longerwavelengths. In Chapter 4we will showthat despite the reduced performance due to the lower technological status, gas spectroscopy can still be feasible with such devices. Besides the spectroscopical applications photonic integrated circuits can find use in the field of distance metrology. A setup verified the feasibility of a modelocked laser in combination with a VIPA spectrometer to obtain metrological data with a single camera image, which is demonstrated in Chapter 5. This chapter also concludes the investigation of monolithically integrated laser sources.
In addition to on-chip lasers, this work investigates fiber-based frequency comb lasers. With a much lower repetition frequency in comparison to integrated pulsed lasers, the corresponding mode-spacing in the frequency domain sets different requirements of the spectrometer. On the other hand the denser and yet wider spectral coverage allows for spectroscopy over a wider range of absorption lines. Chapter 6 is dedicated to introduce frequency comb lasers and the virtually imaged phased-array (VIPA) spectrometer. The combination of both is used to determine the temperature of CO2 by looking at its absorption behaviour. Similar measurements have been executed in ambient air and are summarised in Chapter 7. Due to the low concentration of CO2 in ambient air, this required a very long path length. In Chapter 8 we demonstrate an optimised setup to increase the stability of the method introduced in Chapter 6. The improved setup is more stable with respect to ambient fluctuations and is portable, which allows measurements outside of laboratory conditions. The final chapter, Chapter 9, summarises the results of all the presented experiments and discusses the impact it can have on future devices making use the presented methods.

Integrated Optics
Frequency Comb
Spectroscopy
Virtually Imaged Phased Array

https://doi.org/10.4233/uuid:99887eda-5264-4564-888e-dcaf2dbae356

978-94-028-1084-4

Institutional Repository

doctoral thesis

© 2018 A. Hänsel