Professional teeth whitening can cost anywhere from $300 to $1,000. It’s no surprise many people turn to over-the-counter strips, kits and toothpaste to brighten their smiles. "Think of ...

Figure 1: The terahertz gap. The gap, lying roughly between 300 GHz (0.3 THz) and 30 THz, exists because the frequencies generated by transistors and lasers, typical semiconductor devices, don't ...