What is the difference between argon laser and yag laser?

Wavelength of light: Medical lasers work by using electrical energy to excite a "laser medium". The laser medium can be a natural or synthetic substance such as a gas (e.g. Argon), a liquid or a solid (e.g. Yag) . When excited by electricity these substances give off light energy of a unique wavelenth. Some wavelengths of light heat tissue, while others are absorbed by colored molecules such as melanin or hemaglobin.

Yes: wavelengths: Argon lasers are 480-520nm range: absorbing into red ie red vessels and melanin. Yag however: is of 1000nm and upwards, ie non visible light and has mostly absorption of dark blue/brown and protein. That means argon is good for red vessel ablation and yag is better for hair and blue black vessels but also it is safer for darker skinned patients.