Nonlinear optics. a field that explores the interaction between light and matter. deals with material systems that exhibit nonlinearity depending on incident light intensity. These interactions can give rise to new light frequencies. modify polarization. and manipulate space and time. Titanium dioxide TiO2 is a common material used in this field. known for its wide bandgap semiconductor properties that result in strong nonlinear optical effects suitable for various photonics applications. Its high bandgap contributes to large third-order optical nonlinearities. leading to effects like third-harmonic generation and multiphoton absorption. The fabrication process plays a role in the variability of TiO2's optical properties while patterns on the film can enhance them. In addition to these properties. TiO2 also possesses qualities such as a high refractive index. chemical stability. biocompatibility. and non-toxicity which make it suitable for other uses such as photovoltaics. photocatalysis. sensors. and optical waveguides. One significant application of TiO2's nonlinear optical properties is in the fabrication of photonic devices like optical switches and wavelength converters utilizing phenomena such as three-photon absorption and the Kerr effect.

Polypropylene. a commonly used plastic in various applications such as packaging and textiles. differs from perfluoroalkyl substances PFAS. which are man-made chemicals used to protect against water. oil. and sewage. These PFAS chemicals are often referred to as timeless chemicals due to their long-lasting presence in the environment and human bodies.

Unlike PFAS. polypropylene itself does not contain or require these chemicals for its production or performance. However. it is important to note that while plastics like polypropylene do contribute to broader environmental contamination issues including PFAS. this is not directly related to concerns about sustainability or chemical safety.

Titanium Dioxide can be found in various food products such as:
1. Confectionery – used in sweets for its brightness, such as hard candies, chewing gums, chocolates, and donuts.
2. Baked goods – used to provide a brighter white color, such as bread and cakes.
3. Milk and dairy products – used for its brightening properties, such as cheese and yogurt.
4. Sauces and dressings – used to provide a smoother texture.
5. Processed foods – used to maintain a consistent color, such as ready meals and fast food.
6. Supplements and Medications – used as a colorant and also to keep tablets from sticking to each other during production.
Additionally, it can also be found in toothpaste and some cosmetics in order to achieve a white or opaque color.