Linear and nonlinear optical properties of DNA suspensions

DNA has a helical arrangement, consisting of hundreds of millions of base pairs, whose length and configuration depend on the type and origin of DNA. In this work, we investigate the differences in the linear and nonlinear optical properties of circular-shaped plasmid DNA, small-stranded lambda DNA, and extra-long strands of strawberry DNA under the illumination of a 532 nm laser. We compare the linear absorption spectra of each type of DNA and determine the possible damage to DNA after 1 hour of exposure to high-power green laser. Surprisingly, linear absorption spectra and electrophoresis did not detect any significant damage to all 3 types of DNA. Then we use the Z-scan method to determine the nonlinear absorption and nonlinear index of refraction for each DNA. Our results showed that DNA is a moderately nonlinear photonic material with nonlinear coefficients similar to organic polymers.