Absorption and Reflection Spectra of Lichen

Posted on: April 27th, 2020

Absorption and reflection spectra can reveal the unique properties of many different types of materials and samples. This includes biological samples and plant life. This can range from leaf’s, flower petals, grass and lichen. The optical properties of lichens have been traditionally explored in the context of geological mapping where the encrustation of lichens on rocks may influence the detection of minerals of interest. As of today, several studies have looked into the potential of using the optical properties of lichens to classify them, such as reflection and absorption of light. Avantes equipment is well suited for these types of applications

Fig 1. Absorbance/Reflection system setup with microscope attachment

Conducted by: David Ademe, Avantes Inc.

Description of System:

A white LED light source is ideal for absorption and reflection measurements because of its power and good output in the VIS range, which is the wavelength range many researchers use to characterize reflection, absorption and fluorescence in the visible range. The white LED light source used in this testing is a ring light for the stereoscope that was used to obtain the close-up views of the lichen samples. The ring light is mounted to the base of the stereoscope to illuminate the samples. From there, the scope is adjusted to optimal magnification to view the lichen up close. A fiber bundle is connected to one of the ports of the stereoscope, which feeds the light directly to the spectrometer.

For this experiment, the AvaSpec-Mini2048CL was used. The AvaSpec-Mini-CL series can be equipped with a 2048-pixel CMOS detector or our first-to-the-market 4096-pixel array. Enjoy the speed and enhanced native UV/NIR response of CMOS with an incredible resolution of up to 0.09 nm unavailable anywhere else. The low stray light design allows stray light levels from as low as 0.2% and the fast response time boasts data transfer speeds as fast as 4.6 ms/scan and integration times ranging from 30 µs to 50 s. The configuration used in this testing is optimal for absorbance and fluorescence measurements as it is fitted with a 200-um slit. In addition to the large slit, this Mini is configured with an OSC-UA and OSF-305.

Description of Methodology:

For this experiment, we used the absorbance and reflection modes in AvaSoft. These modes are built to capture the absorbance of samples in absorbance units and the reflectance of samples in percent, respectfully.

Our setup will be used to measure the absorbance and reflection spectrum of three different types of lichen. Lichens occur in one of four basic growth forms:

• Crustose – crust-like, growing tight against the substrate.
• Squamulose – tightly clustered and slightly flattened pebble-like units.
• Foliose – leaf-like, with flat sheets of tissue not tightly bound.
• Fruticose – free-standing branching tubes.

For this experiment, we were able to obtain lichen in three of is basic growth forms: crustose, squamulose and foliose.

A WS-2 reflection tile will be used as our reference. With the tile, we will use this to optimize the integration time and averaging for the spectrometer in the VIS wavelength range.

Test Data and Results:

Displayed below is the reflectance and absorption spectrum collected from the three lichen samples.
Integration time: 500 ms
Averaging: 100

Get the Downloadable Data Files

Absorption and Reflection Spectra