**Core Concept**
The management of after cataracts, also known as posterior capsule opacification, involves the use of laser therapy to create a clear opening in the opacified posterior capsule. This is achieved through a process called capsulotomy.

**Why the Correct Answer is Right**
The correct answer is **Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser**, which emits a high-intensity infrared beam that is selectively absorbed by the water molecules in the opacified posterior capsule. This absorption causes a rapid increase in temperature, leading to the formation of a clear opening in the capsule. The Nd:YAG laser is specifically designed for this purpose and is widely used in ophthalmology for posterior capsulotomy.

**Why Each Wrong Option is Incorrect**
**Option A:** Argon laser is incorrect because it emits a blue-green beam that is primarily used for photocoagulation in diabetic retinopathy and other retinal diseases.
**Option B:** Excimer laser is incorrect because it emits a high-intensity ultraviolet beam that is used for corneal surface ablation in refractive surgery, such as LASIK.
**Option C:** Krypton laser is incorrect because it emits a red beam that is used for photocoagulation in retinal diseases, but not for posterior capsulotomy.

**Clinical Pearl / High-Yield Fact**
The Nd:YAG laser is a high-energy laser that requires precise control and a skilled operator to avoid complications such as retinal damage or posterior vitreous detachment.

**Correct Answer: D. Nd:YAG laser**