Efficient integration between an integrated optics Raman spectrometer and a CMOS based photo detector
Dirk Reith, Ewoud van Lent, Zeno Geuke, Martijn Blom, Gijsbert van den Engh
Table of Contents
Part 1: The research page 3
Introduction page 4
Chapter 1: Raman Spectroscopy page 5
Chapter 2: Integrated Raman Spectroscopy page 9
Chapter 3: The Experiment page 12
References page 19
Part 2: The research group page 20
Introduction page 21
Chapter 1: IOMS in general page 22
Chapter 2: The Chairman interview page 23
...view middle of the document...
Using Raman spectroscopy one is able to detect the compositions of certain molecules, like a fingerprint, having the (infrared) frequency corresponding to the vibrational and the rotational modes
Raman spectroscopy is based on the Raman scattering, which is also called inelastic scattering, this is the scattering of monochromatic light, which usually origins from a laser with a range near the infrared or ultraviolet, more about this later.
Raman spectroscopy is much like infrared spectroscopy, as they both rely on the shift in energy states in vibrations and rotations, however infrared spectroscopy is based on the absorption of the light whereas Raman spectroscopy is based on the scattering. The fact that they are both based on another principle makes them a good combination to gain information about a certain vibration or rotation, as in some occasions infrared spectroscopy can’t give you enough information about the to be analyzed material, e.g. when there is a certain symmetry, where Raman spectroscopy can, and vice versa. Therefore it is recommended to use both spectroscopic techniques to gain more useful and specific information about certain modes in a system.
Figure 1.1 Energy level diagram showing the states involved in Raman signal. 
As mentioned before, Raman spectroscopy is based on Raman scattering, which is the inelastic scattering of a photon, for example certain in molecules in human tissue. When a photon interacts with the material, for instance a liquid, solid or gas, and the frequency of this photon shifts to either red or blue. A blue shift can be seen as the photon gaining energy from the material, whereas a red shift can be observed as the photon depositing energy to the material, these shifts are called the
Raman shifts. And they are characteristics for the molecules that are observed.
However, the Raman scattering is very weak, and one of the principally difficulties in Raman spectroscopy is to segregate this scattering from the way more intense Rayleigh scattering. Rayleigh scattering occurs when there is no energy shift between the incoming and outgoing light. There are more scatterings though, for example fluorescence, which also has to be segregated before you can measure the Raman scattering.
As the Raman scattering is very weak, typically varying from 10-9 to 10-6 of the intensity of the other scatterings, it is difficult to observe the Raman scattering without a very sensitive detector or intense monochromatic excitation. But now, as there has been found a solution to overcome the difficulties in separating the scatterings it is becoming easier and easier to separate them.
A schematic Raman spectrometer
On the right you can see a simple schematic drawing of a modern Raman spectroscopic instrument, showing the main parts of the system.
Figure 1.2 Schematic of laser Raman instrumentation. 
At first the laser, to create a light beam, then a mirror is used to reflect the light...