Luna Optoelectronics' silicon avalanche photodiode (Si APD) is a photon detection device that offers high internal gain. It is ideal for use in high speed, low light level applications. As with conventional photodiodes, absorption of incoming photons creates electron-hole pairs, also known as carriers. Because of an APD's internal structure and a much higher reverse bias voltage, a strong internal electric field accelerates the carriers, and these carriers then produce secondary electron-hole pairs by the process of impact ionization. A standard PIN photodiode has unity gain, and an APD produces a gain of up to several hundred. An APD's greatest advantage over traditional photodiodes is improved S/N ratios. Luna Optoelectronics also offers several patented large area configurations (LAAPD) enhanced for a variety of regions of the spectrum. These are available with built-in thermoelectric coolers to reduce the dark current and enhance performance. Package options include hermetically sealed windows or windowless configurations.