A laser diode, also known as an injection laser or diode laser, is a semiconductor device that produces coherent radiation (in which the waves are all at the same frequency and phase) in the visible or infrared (IR) spectrum when current passes through it.
IPL is a popular hair removal treatment that helps kill the hairs, so they don’t come back. Unlike laser hair removal, IPL does not use a laser light source but instead uses a broad spectrum high-intensity light that emits light at multiple wavelengths. While laser devices emit one single focused wavelength to maximize follicle absorption, IPL covers larger patches of hair. IPL is like using a strong light bulb and is usually cheaper than laser treatments.
A ruby laser is "A laser that uses a ruby crystal to produce an intense narrow beam of coherent red light, used in light transmission communication and for localized heating." (Free dictionary definition). Some input from Wikipedia about ruby lasers: A ruby laser is a solid-state laser that uses a synthetic ruby crystal as its gain medium.
Ytterbium (Yb) is a chemical element belonging to the group of rare earth metals. In laser technology, it has acquired a prominent role in the form of the trivalent ion Yb3+, which is used as a laser-active dopant in a variety of host materials, including both crystals and glasses.