A natural dye extract from indigo has the potential to protect our eyes from the harmful laser

Researchers from the @RRI_Bangalore and Kensri School and College, Bengaluru, researched on optical properties of the natural Indigo dye and found out that Indigo dye can act as a device to protect human eyes from harmful laser radiation. Read:
@IndiaDST

Researchers from the Raman Research Institute (RRI) and Kensri School and College, Bengaluru, have found out that the natural indigo dye extract is capable of protecting human eyes from harmful laser radiation.

The findings of the study reveal that the natural indigo dye extracted from leaves of a plant of the bean family can develop optical limiters useful in weakening the potentially harmful radiation and protecting the human eyes or other sensitive optical devices from accidental damage in an environment where such lasers are in use.

The study was funded by the Department of Science and Technology, Ministry of Science and Technology, India and was published in the journal ‘Optical Materials’.

The interesting findings of the study suggest that the leaves of the ‘true indigo’ plant could be used to develop optical limiters useful in incapacitating the potentially harmful radiation, thus, protecting the human eyes or light detectors from harmful laser radiation.

The research extract suggests that this is the first such study carried out in Indigofera Tinctoria natural dye extract.

*True Indigo:*

To conduct the experiment true indigo or scientifically referred to as Indigofera Tinctoria is used. It is a species of plant from the bean family and is widely used to produce indigo dye. The blue dye extracted from Indigofera Tinctoria is commonly used in India and across the globe in the fabric industry. Even though synthetic indigo dyes are now available, the natural variety is still used as a sustainable practice. The indigo hair colour is also one of the natural hair colouring material commonly used today.

*How much indigo absorbed light at different wavelengths of the electromagnetic spectrum?*

To preserve the natural properties of the Indigofera Tinctoria natural dye extract, researchers stored it in a refrigerator below 4º Celsius.

Then they studied how much indigo absorbed light at different wavelengths of the electromagnetic spectrum, which showed that the absorption is maximum in the UV region of the spectrum, at a wavelength close to 288 nanometres, and in the visible region, close to 660 nanometres. The absorption is comparatively high for the green light as well.

*Reji Philip, professor at RRI and a co-author of the study explains how indigo could be a potential optical limiter*

“Indigo absorbs light because of molecular absorption bands. The maximum absorption wavelength can vary over several nanometers depending on the dye’s solvent and concentration,” explains Reji Philip, professor at RRI and a co-author of the study.

The absorption’s variation with wavelength indicated that chlorophyll, an organic compound found in leaves that helps part in photosynthesis, is present in the dye.

While studying whether the organic dye showed additional absorption when the input light intensity is high, they found out that an increase in the intensity of the laser pulse makes the dye absorbs more light.

Optical limiters are useful in weakening the potentially harmful radiation emitted by powerful lasers and protecting both eyes and sensitive optical instruments.
“Making a prototype optical limiter using natural Indigo is the next logical step, followed by a commercially viable product,” Reji pointed out.

*How the study was conducted?*

-In the study, the scientists have extracted the natural dye ingredient found in Indigofera Tinctoria leaves and investigated its nonlinear optical absorption by employing the Z-scan technique.

-The dye is extracted from Indigo powder i.e. commercially available for hair colouring applications.

-The powder is made from grinding Indigofera Tinctoria leaves into fine particles.

-Then the powder is mixed with water, sonicated, centrifuged.

-After which it is filtered to give an optically clear extract.

-Linear absorption of the extract is measured in the visible spectral region using a spectrophotometer.

-Nonlinear absorption in the green spectral region is measured using 5 ns (5 × 10−9 s), 532 nm laser pulses obtained from a frequency-doubled Nd: YAG laser.

*What was the finding?*

-The Indigofera Tinctoria dye is found to show excellent nonlinear absorption. That arises from strong reverse saturable absorption occurring in the sample at this wavelength.

– The third-order nonlinear absorption coefficient, which is obtained by numerically fitting the Z-scan data to the nonlinear transmission equation, has a high value in the order of 10−10 m/W.

-This high nonlinear absorption, which is in the same range as that of materials such as graphene oxide, leads to an excellent optical limiting behaviour, making Indigofera Tinctoria a potential candidate for fabricating optical limiter devices for eye and sensor protection.