Mid-IR FlexIR™: The Next Generation of Mid-IR Remote Sampling Accessories
(Excerpts from the application note by Jenni Briggs, PhD – PIKE Reflections, Spring 2011)

PIKE Technologies recently introduced the next generation of commercially-available FTIR remote sampling accessories with the Mid-IR FlexIR™. Hollow waveguides (HWGs), the cornerstone of this mid- IR remote sampling accessory, offer enhanced performance characteristics compared to traditional Mid-IR optical fibers. The most popular type of HWGs consists of reflective coated silica tubing. The inner portion of silica tubing is coated with Ag, followed by the convertion of some of the Ag to AgI to form a dielectric layer, which exhibits a highly reflective and very smooth surface. The exterior of the silica tubing is coated with acrylate polymer to provide additional strength. Before now, HWGs found limited use in commercial spectroscopy.

A HWG has been used as an alternative to a mirrored gas cell by introducing both the analysis gas and the IR beam into the HWG. Also, HWGs have been used as CO2 and Er:YAG laser delivery vehicles, and as a bidirectional transmission device for the delivery and collection of Raman scattering. The diverse capabilities of the newest technology in mid‐IR remote sampling are illustrated well by the following three examples of spectra collected with the attenuated total reflectance (ATR), diffuse reflectance, and specular reflectance sampling probes.

Biomedical Application: ATR Probe

The objective of this biomedical application was to look at residual chemicals found on human skin after the application of a commercially‐available sunscreen spray. A spectrum was collected before and after the application of the skin care product using the FlexIR ZnSe ATR probe. Spetra collected in this experiment are shown below.

Intractable Panels: Diffuse Reflectance and Specular Reflectance

Reflective‐type measurements may be classified as either diffuse or specular. Coatings and thin films on reflective substrates are candidates for specular reflectance measurements. Using this sampling technique the reflected beam from the sample is collected at an angle of incidence equal to that of the incoming beam as it is delivered to the sample. Diffuse samples scatter the reflected beam across a wide range of angles and in IR sampling must be gathered using a collection optic. The following spectra illustrate composition of a coating on a smooth reflective surface obtained by using the Mid‐IR FlexIR configured with a specular reflectance probe. The last figure contains spectra of painted diffuse panels collected with the diffuse reflectance probe

Comments

HWGs bring new technology to mid‐IR remote sampling accessories. The diversity of sampling probes covering ATR, diffuse reflectance, and specular reflectance used in conjunction with HWGs and high precision optics offers the capability of collecting quality spectra of a wide range of samples, which may be prohibited with traditional in‐compartment FTIR sampling accessories.