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Two laser beams cross in a glass cuvette that holds a
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Two laser beams cross in a glass cuvette that holds a transparent liquid.

May 7, 2010
Two laser beams cross in a glass cuvette that holds a transparent liquid. Electrodes are suspended in the glass cell so that an electric field can be applied in the region where the laser beams interact with the molecules in a solution. The cell was used to observe a new electrooptic effect. This research was conducted with the support of National Science Foundation grant CHE 00-95056.

More about this Image This image shows a cuvette made from quartz glass that researchers from Cornell University have used to observe a new electrooptic effect. A red and a blue laser beam from a femtosecond laser can be seen crossing in the cuvette between electrodes suspended from above and below. The light pulses are so intense that they cause the molecules in the solution to emit radiation at the sum of the incident frequencies. Here the sum-frequency is in the ultraviolet and is not seen in the image. This nonlinear optical process is known as "sum-frequency generation." For symmetry reasons, sum-frequency generation can in a liquid only take place if the molecules are handed.

Just as gloves and hands come in mirror-image pairs (a left and a right), many molecules can exist in "left" and "right-handed" forms. This property of handedness is called chirality and most biological molecules including proteins, DNA and their building blocks are chiral. Surprisingly, all living organisms contain only "left-handed" amino acids and "right-handed" sugars. This exclusive homochirality (having all molecules of one type of the same handedness) has the important consequence that the biological and pharmaceutical activity of many molecules is often directly related to their chirality. The fundamental importance of chirality in chemistry and biology requires probes that are sensitive enough to distinguish between the two mirror-image forms of a chiral molecule, and optical methods are often the only practical physical means to do so.

Using the liquid-cell shown in the image, researchers from Cornell University have showed that the application of a static electric field to sum-frequency generation can be used to distinguish between the "left-" and "right-handed" forms of chiral molecules in solution. (Year of image: 2003)