Which type of laser is characterized by having a medium made of dye?

Dye lasers are specifically designed to use organic dye as their gain medium. This type of laser operates by exciting the dye molecules, allowing them to emit light at various wavelengths depending on the specific dye used. The ability to tune the wavelength is one of the key advantages of dye lasers, making them versatile for applications that require different light wavelengths.

In contrast, solid-state lasers utilize solid materials like crystals or glass as their gain medium, gas lasers use gases, and semiconductor diode lasers rely on the properties of semiconductors. These other types do not use dyes, which is the defining feature of dye lasers. Therefore, recognizing the unique medium of dye in this context clarifies why dye laser is the correct answer.