**Core Concept**
The question is testing the student's knowledge of the types of lasers used in ophthalmology, specifically for capsulotomy. Capsulotomy is a surgical procedure to create an opening in the posterior capsule of the eye, usually after cataract surgery. The correct answer requires an understanding of the different types of lasers and their applications in ophthalmology.

**Why the Correct Answer is Right**
Nd:YAG (Neodymium-Doped Yttrium Aluminum Garnet) lasers are commonly used for capsulotomy due to their ability to transmit high-powered pulses of infrared light. This energy is selectively absorbed by the posterior capsule, causing it to break down and create an opening. The Nd:YAG laser has a wavelength of 1064 nm, which is ideal for this application. The precise energy delivery and controlled breakdown of the capsule make Nd:YAG lasers the preferred choice for capsulotomy.

**Why Each Wrong Option is Incorrect**
**Option A:** CO2 lasers are primarily used in ophthalmology for surface procedures such as skin resurfacing and pterygium removal, but they are not suitable for capsulotomy due to their wavelength and energy characteristics.

**Option B:** Ruby lasers are an older type of laser that were used in ophthalmology for retinal photocoagulation, but they are not used for capsulotomy. Their wavelength and energy delivery are not ideal for this specific application.

**Option D:** Argon lasers are also used in ophthalmology for retinal photocoagulation and laser trabeculoplasty, but they are not suitable for capsulotomy. Their wavelength and energy characteristics make them less effective for this procedure.

**Clinical Pearl / High-Yield Fact**
When performing a Nd:YAG capsulotomy, it's essential to ensure proper patient selection and preoperative evaluation to minimize the risk of complications, such as posterior capsule rupture or retinal damage. A thorough understanding of the laser's energy delivery and the patient's eye anatomy is crucial for successful outcome.

**✓ Correct Answer: C. Nd:YAG**