Figure 1: Photograph of the 1.4.3 FTIR spectromicroscopy endstation.

Introduction

The FTIR instrumentation for Beamline 1.4.3 is shown in Figure 1 and consists of a Nicolet 760 FTIR bench (to the left), a Spectra-Tech Nic-Plan IR microscope (in the center), and video display and stage controller for the microscope (on the right). One of the primary reasons for doing infrared spectroscopy at a synchrotron light source is the large enhancement in brightness (flux per unit area). This brightness advantage manifests itself most beneficially when focussing the light to a very small spot size. We have been able to achieve essentially diffraction-limited spot sizes in the mid-IR using the Nic-Plan microscope with the ALS source.

The collimated synchrotron light beam exits the switchyard at its lower left and then enters the beamline 1.4.3 hutch through a hole in the wall. The light is reflected behind the Nicolet 760 bench all in rough vacuum. The beam exits the vacuum via a diamond window and then enters into the side of the Nicolet bench. Once inside the bench, the light goes through the FTIR Michelson interferometer, then is sent on to the sample which can be either in the main bench’s sample compartment or in the Nic-Plan IR microscope, and finally to an IR detector. As the microscope is where large advantages are gained from coming to a synchrotron IR beamline, this manual will concentrate on describing the operations of the IR microscope.

When you first arrive at the beamline there are several things to do. The main FTIR bench and the IR microscope are always kept powered on, but the Mercury-Cadmium-Telluride (MCT) IR detector inside the microscope needs to be cooled by filling its dewar with liquid nitrogen. A funnel is built in to the top right of the microscope (gray flip top on a blue plastic mount) and is connected to the MCT’s vacuum-insulated dewar. Open the flip top, and slowly pour in liquid nitrogen. A green thermos labeled ‘Nicolet’ holds approximately the correct amount of liquid nitrogen to fill the MCT detector’s dewar. When first beginning to fill, pour in only enough liquid nitrogen to fill the funnel (you will see it start to bubble against the plastic screen), and then stop pouring for at least 60 seconds and let that amount drain down the funnel. Repeat this two or three more times to fully cool down the funnel and tubing system. Then slowly pour the rest of the liquid nitrogen into the funnel making sure to never overflow the funnel. Store the empty green thermos face down on the ground. Please wear safety glasses and cryogenic gloves for this operation. If there is no liquid nitrogen in the 4 L dewar, you may fill it at the user liquid nitrogen station (please see the FAQ for directions). The dewar will typically remain cold for > 10 hours, but you should keep track of when you filled it so that the detector does not get warm over a long measurement!