What optics are used on a flow cytometer?

The optics used on a flow cytometer include three main parts: lasers, filters and mirrors, and detectors.

• Lasers: Lasers are the most common excitation light sources on flow cytometers, e.g. 355 nm UV laser, 405 nm violet laser, 488 nm blue laser, 532 nm green laser, 561 nm yellow laser and 640 nm red laser. They are responsible for illuminating the cells with uniform light of a specific wavelength. One or more laser lines are usually used on a single flow cytometer, which can be arranged in a co-linear and/or parallel manner.
• Filters and mirrors: Filters and mirrors are used to guide the path of light. Different filter types, such as longpass (LP) filters, shortpass (SP) filters and bandpass (BP) filters, can be employed for different purposes. Dichroic mirrors, also known as dichroic beamsplitters, are critical in directing and capturing light. They are essentially the combination of a mirror and a filter, who can pass light in a certain range and also reflect light in another range. For example, a 500LP dichroic mirror can transmit light above 500 nm and reflect the light below 500 nm in a different direction.
• Detectors: Detectors capture the photons and convert them into photocurrent which can later be detected by the electronic system. The most common types of detectors used on a flow cytometer are the photodiode (PD) and the photomultiplier tube (PMT).