Optical Couplers: Key Hardware for High Quality FTIR Spectroscopy
Figure 1: Optical Coupler
Figure 2: Optical Couplers on each side of Cell
Optical couplers are used to take the light coming from the source of a FTIR and route it through the sampling accessory and into the FTIR detector. This is an essential process in the effective use of the FTIR spectrometer. Therefore, optical couplers play an essential role in the proper use and maintenance of a FTIR system. Recognizing the importance of optical couplers to the overall effectiveness of the FTIR System, CIC Photonics has developed their own design for optical couplers.
The purpose of optical couplers is to direct light efficiently to the desired locations. Two essential issues must be addressed when implementing optical couplers: the couplers must efficiently transfer light to the location of interest, and they must be able to maintain this efficient transfer throughout the life span of the instrument. CIC Photonics optical coupler design has numerous features which address these key issues as well as a number of secondary issues of lesser importance.
To address the issue of efficient light transfer, the CIC Photonics optical coupler design uses an off-axis parabolic mirror to transfer the light from the source to the FTIR sampling accessory (e.g. a gas cell) and from the accessory to the detector. In order to adjust for small variations in the optical path and provide the means of correcting these variations (alignment), CIC Photonics optical couplers use a set of three alignment screws on top of the off-axis mirror which imparts small changes in the mirror position. Once the optimal throughput has been obtained, the mirror is locked into place with a second set-screw.
In order to maintain the optical efficiency earned in proper alignment, CIC Photonics has implemented a system of hard-mounted optical couplers. Our couplers are made of rigid aluminum fixtures which are bolted together to eliminate undesired degrees of freedom. This means that the couplers will not rotate or slip down and out of alignment. Different optical coupler heights are developed through the use of height sleeves which hard mount to the other coupler components. This optical coupler design, developed by CIC Photonics, offers significant advantages in rigidity and in the ability to maintain the optical path in instrument installations throughout the world. The robust design of the CIC Photonics optical coupler means that traveling instruments like the IRGAS-100MT™, once aligned, stay aligned. In the end, that means the instrument is ready to run when the customer takes it out of the box!
The IRGAS XFlo™ gas analysis system is based on the combination of the rugged Bomem WorkIR process FTIR with a flanged "White Cell" design. This package offers the user the capability to mount the FTIR system directly into process exhaust flanges. This, in turn, makes the Xflo™ system ideal for monitoring abatement tools, multiple process tools, and other high-flow, low-concentration applications. In addition, the excellent sensitivity characteristics of the XFlo™ system make it suitable for measuring process tool progress in order to determine the presence of undesirable impurities or end-points. For more information on the XFlo™ gas analysis system or any other CIC Photonics product, please do note hesitate to contact us at the address above.
1 High-Sensitivity, Fast-Response Monitoring of PFC and Abatement Tool Emissions By FTIR Spectroscopy, Perez, J.E. and Meyer, R. T., Semicon West 2003 Technical Symposium.
2 Multiple Gas Impurity Analyses and Verification For Semiconductor Process Tools, Meyer, R.T., Gases and Technology, January/February 2003