**Core Concept**
Posterior capsulotomy is a surgical procedure performed to treat posterior capsule opacification (PCO) after cataract surgery. PCO is a common complication where the posterior capsule, which holds the intraocular lens (IOL) in place, becomes cloudy, affecting vision. The goal of posterior capsulotomy is to create a clear opening in the posterior capsule, allowing light to pass through.

**Why the Correct Answer is Right**
Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser is used for posterior capsulotomy because it emits a high-intensity infrared beam that can precisely cut through the cloudy posterior capsule. The Nd:YAG laser works by creating micro-explosions within the tissue, breaking down the opacified capsule and creating a clear opening. This procedure is typically performed in an outpatient setting, with minimal discomfort and no need for stitches.

**Why Each Wrong Option is Incorrect**
**Option A:** Argon Laser is primarily used for treating retinal tears and detachment, as well as for panretinal photocoagulation in diabetic retinopathy. It is not suitable for posterior capsulotomy due to its lower intensity and different wavelength.
**Option C:** Holmium laser is used in urology for procedures such as laser lithotripsy and prostate surgery. It is not commonly used in ophthalmology for posterior capsulotomy.
**Option D:** Diode laser is used in various ophthalmic procedures, including panretinal photocoagulation and retinal vein occlusion treatment. However, it is not the preferred choice for posterior capsulotomy due to its lower precision and higher risk of complications.

**Clinical Pearl / High-Yield Fact**
It's essential to note that posterior capsulotomy should be performed only after the posterior capsule has become significantly opacified, as premature treatment can lead to complications such as capsular rupture or retinal damage.

**✓ Correct Answer: B. Nd YAg**