Transmission/Reflection Measurement

Transmission/reflection spectroscopy is an important optical property of materials themselves. With the booming development of industry today, the quality control of material properties is becoming increasingly strict. Therefore, the use of fiber optic spectrometers for rapid and accurate measurement of transmission/reflection spectra is becoming increasingly mature. For different types of samples, in order to obtain better spectral data, the two basic modes of transmission and reflection will evolve into more forms.

Reflectance measurement

1. Reflection is usually divided into specular reflection and diffuse reflection. When the incident light undergoes specular reflection on the surface of an object and is measured by a reflection probe (FCR), it can easily cause saturation of the spectrometer, and is greatly affected by changes in measurement distance and direction. To ensure measurement accuracy, the distance from the probe to the surface of the object must be consistent with the distance from the probe to the mirror reference (RS-2).

2. When the incident light undergoes diffuse reflection on the surface of an object, using a reflective probe or integrating sphere yields similar measurement results.

3. Measurement repeatability can be ensured within 1% using an integrating sphere.

4. To avoid saturation of the spectrometer, a reflective integrating sphere (AvaSphere REFL) can be used. Its inner surface is a uniform diffuser with very uniform spatial reflection characteristics. After multiple reflections on the inner surface, the specular reflection light has the same intensity at any position on the inner wall of the integrating sphere. The measurement steps are as follows: first, place the standard piece at the sampling port of the integrating sphere as a reference for measurement, and then place the sample to be measured at the sampling port. The software will automatically calculate the reflectivity R.
5. The standard film includes WS-2 diffuse reflection and RS-2 specular reflection.

Transmittance measurement

1. For the measurement of transmittance of various optical materials such as glass, plastic, crystals, films, etc., a CUV-UV/VIS sample holder (Figure 4) can be used, and the two ends of the holder are connected to a spectrometer and a light source through optical fibers. Measurement steps: First, measure the light intensity P1 when no sample is placed in the optical path as a reference. Then, place the sample to be tested in the sample holder and measure the transmitted light intensity P2. The software will automatically provide the transmittance T.

2. For some special measurements, such as illuminating samples at different incident angles to measure the changes in material transmittance, a transmissive integrating sphere (Figure 5) is required.

Measurement steps: The light source is connected to a fiber optic output light, which is collimated by a lens and directed into the sampling port of the integrating sphere. The measured light intensity P1 is saved as a reference, and the sample to be measured is placed in the sampling port of the integrating sphere. The collimated light passes through the sample and enters the integrating sphere, where the light intensity P2 is measured. The software automatically calculates and obtains the transmittance T.