Use of YAG (Yttrium Aluminum Garnet)

Use of YAG (Yttrium Aluminum Garnet)

Use in Medical Treatment:

A cataract is much like a smartie or M&M. It has an outer coating (capsule) and an inner nucleus (the chocolate in the smartie). When an eye surgeon performs cataract/lens surgery the surgeon makes a circular opening in the front facing capsule of the lens and then removes the inner nucleus. The remaining capsular envelope supports the new artificial lens which is typically injected in through the opening in the capsule. Over time the capsule shrinks and wraps around the new lens much like shrink wrap or cling film. As the capsule contains live cells some capsule can develop a layer of new cells that form a frosting on the back surface of the lens. This is called posterior capsular opacification (PCO) or an after-cataract and can occur in up to 10% of patients after lens/cataract surgery. The frosted layer is much like the frosting on a window which can blur the view through the window and similarly through the new lens. PCO can occur at any time after surgery including a few weeks to months later. In some surgeries an adherent plaque may be present on the capsule and a surgeon may prefer to leave this rather than risk tearing the capsule. In these cases early treatment to clear the frosting may be necessary.

Cerium-doped Yttrium Aluminum Garnet Properties (Theoretical)

Compound Formula	CeY3Al5O12
Molecular Weight	733.734
Appearance	Crystalline solid
Melting Point	1965-1970 °C
Boiling Point	N/A
Density	4.55 g/cm3
Refractive Index	1.82-1.83
Crystal Phase / Structure	Cubic
Tensile Strength	2 Gpa
Thermal Conductivity	11.2 W/m·K
Thermal Expansion	6.14 x 10-6·K-1

The YAG laser is the laser used to clear the frosting from the back surface of an intraocular lens. YAG laser treatment is painless and is completed from outside the eye in a few minutes. During YAG laser treatment your eye doctor may use a magnifying contact lens to help with aiming the YAG laser at the layer of frosting. During the treatment patients will see flashes of light and hear a clicking sound. The pupil needs to be dilated before YAG laser can be performed to allow a good view of the lens surface. After the treatment your doctor will prescribe a short course of anti-inflammatory and pressure drops. Most patients will noticed an improvement in clarity and vision within a day. YAG laser treatments are typically only needed once as the capsule does not regrow after it is vaporised by the YAG.

Complications after YAG laser are very rare but can in rare cases include vitreous floaters, raised eye pressure, retinal swelling, lens damage and very rarely retinal detachment.

 Use in preparation of White LED:

The GaN-based light-emitting diode comprised a 3 μm thick GaN:Si layer, five pairs of undoped InGaN/GaN multiple-quantum-wells (InGaN-GaN MQWs), and a 0.5 μm thick layer of GaN:Mg sequentially on a (0001) oriented patterned sapphire substrate with a GaN buffer layer that was grown by metal-organic chemical vapor deposition (MOCVD). Ni/Au (45 nm/15 nm thickness) layers are deposited on the p-GaN as ohmic contact, respectively. Next, p-GaN/InGaN-GaN MQWs/n-GaN structure is separated from the sapphire substrate by LLO method using 248 nm KrF laser after bonding to glass temporary substrate. The wafer was etching using KOH solution for 30 min to remove residue gallium oxide. The surface of the n-GaN epitaxial layer was observed hexagonal pyramid hillocks. Then, the structure was transferred onto the YAG-PDMS substrate with ITO contact layer to complete the GaN-based white LEDs. demonstrates the structure of the GaN-based LEDs on the YAG-PDMS substrate.

By

Professor,

Mr. Hojiwala Robin A.

Mahavir Swami Polytechnic, BMEF - Surat.