**Core Concept**
Nd-YAG (Neodymium-doped Yttrium Aluminum Garnet) laser is specifically used in the treatment of posterior capsule opacification (PCO), commonly known as after-cataract, where clouding occurs behind the artificial lens after cataract surgery.

**Why the Correct Answer is Right**
Nd-YAG laser delivers a high-energy pulse that photodisrupts the opaque posterior capsule without damaging surrounding tissues. It works via selective photothermal effect, targeting water molecules in the lens capsule. This procedure, called YAG laser posterior capsulotomy, is widely performed in ophthalmology to restore visual clarity by creating a clear opening in the posterior capsule.

**Why Each Wrong Option is Incorrect**
Option A: Argon laser is used for retinal photocoagulation in diabetic retinopathy or retinal detachment, not for posterior capsule opacification.
Option B: Krypton laser is used in retinal treatments like retinal photocoagulation and is not indicated for PCO.
Option D: Excimer laser is used in corneal reshaping (e.g., photorefractive keratectomy) and does not penetrate the posterior capsule.

**Clinical Pearl / High-Yield Fact**
Nd-YAG laser capsulotomy is a quick, outpatient procedure with minimal complications and is the gold standard for treating after-cataracts. It should be performed only after cataract surgery and when visual acuity is impaired due to posterior capsule opacification.

✓ Correct Answer: C. Nd-YAG