Do lightsabers have 2 crystals?

Excuse me, but I must inquire about a specific aspect of a fictional technology. In the realm of the Star Wars universe, lightsabers are renowned for their unique design and functionality. Now, my question is this: Are lightsabers equipped with two crystals within their construction? Is this a standard feature, or does it vary depending on the specific model or design? Your insights would be greatly appreciated as I seek to understand the intricate workings of these iconic weapons.