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Nd:YAG Laser Encyclopedia

Pulished on May. 30, 2022


Light Amplification by Stimulated Emission of Radiation.

Nd.YAG is a simplified name derived from (Neodymium-dopedYttriumAluminiumGarnet; Nd:Y3Al5O12) or yttrium aluminium garnet crystal in Chinese, which is the activating substance. The laser emits at an infrared wavelength of 1064nm.

Generation principle

When the activated material is placed in two parallel mirrors (one with 100% reflection and the other with 50% transmission), an optical resonance cavity is formed in which the non-axially propagating monochromatic spectrum is discharged outside the resonance cavity: the axially propagating monochromatic spectrum travels back and forth within the cavity.

Nd.YAG is its simplified English name, derived from (Neodymium-dopedYttriumAluminiumGarnet; Nd: Y3Al5O12) or in Chinese as yttrium aluminium garnet crystal, yttrium aluminium garnet crystal is its activating substance, the Nd atomic content in the bulk crystal is 0.6 to 1.1%, it is a solid laser, can excite pulsed laser or continuous laser, emitting laser light in infrared wavelengths

When the monochromatic light spectrum propagates back and forth in the laser material, this is called "self-excited oscillation" in the resonant cavity. When the pump lamp provides enough atoms with high energy levels in the laser material, the atoms with high energy levels are subjected to three processes: spontaneous emission transitions, excited emission transitions and excited absorption transitions between the two energy levels. The excited emitted light produced by the excited emission leap has the same frequency and phase as the incident light. When the light is repeatedly passed through the "particle number reversal state" in the resonant cavity, the light intensity of the monochromatic spectrum of the same frequency is increased to produce a laser, and the high permeability of the laser can be emitted through 50% of the transmission mirrors in the resonant cavity to become a continuous laser.


The emission spectrum of the pump lamp is a broadband continuous spectrum, but only a few fixed spectral peaks are absorbed by the Nd ions, so the pump lamp only utilises a small part of the spectral energy, most of the unabsorbed spectral energy is converted into thermal energy, so the energy usage rate is low.

The Nd:YAG absorbs in the spectral region from 0.730μm ~ 0.760μm and 0.790μm ~ 0.820μm. When the spectral energy is absorbed, it causes atoms to jump from lower to higher energy levels, and some of the atoms that have jumped to higher energy levels will then jump to lower energy levels and release a monochromatic spectrum of the same frequency, but the spectrum released has no fixed direction or phase, so it cannot form a laser yet.

Nd:YAG Laser Encyclopedia

System construction

1. Visible laser beam reflector. (for redirecting the visible laser beam into the YAG laser axis)

2. Laser energy detector. (to detect the energy of the YAG laser beam)

3. 100% reflector holder for optical resonance cavity. 4.

4. Base for focal adjustment of optical fibres. (spare)

5. Laser optical resonant cavity with Nd.YAG crystal bar, pump lamp, gold plated reflector cavity.

6. Time-diverging lens. (Moves the lens to send the laser beam out)

7. Energy diverging lens. (diverging the laser beam)

8. Metal laser reflector stopper. (Safety device)

9. Laser beam divergence shutter switch.

10. Optical focusing mirror input for linking optical fibres.

11. Laser energy attenuating lens for adjusting and balancing each diverging output energy.

12. Optical resonant cavity main shutter switch.

13. Visible laser generator, red laser for adjustment.

14. Instrument holder positioning piece. (for installation during relocation only)


The Nd:YAG laser has a wavelength of 1064 nm, which is not near the absorption peak of oxyhaemoglobin, which absorbs the Nd:YAG laser poorly. The Nd:YAG laser has a poor absorption of oxyhaemoglobin, but its penetration depth can be around 8 mm, so it can play a role in the treatment of deeper hemangiomas. The Nd:YAG laser can be divided into two types: continuous and pulsed, according to the different energy output methods. The continuous Nd:YAG laser is currently used, but the thermal damage to the tissue is non-selective, and while the tumour vessels are coagulated, the excess energy can also damage the surrounding normal tissues, leaving scarring easily after the procedure. Therefore, the continuous Nd:YAG laser has been used more often in the fields of ophthalmology, gynaecology and surgery, while in dermatology, it is used with caution because it does not achieve "good cosmetic results". Vlachakis' use of cold ice packs in conjunction with Nd:YAG laser treatment has resulted in a reduction in postoperative scar formation, suggesting that a cooling protection device for the treated area of skin can reduce scar formation. Compared with the continuous Nd:YAG laser, the pulsed Nd:YAG laser is more consistent with the theory of selective photothermal action. Weiss et al. achieved good results with the pulsed Nd:YAG laser in the treatment of vascular diseases. The results of Groot et al. showed that 19% of the lesions were completely cleared after a single treatment and 80% of the patients had more than 50% reduction of the lesions, with minimal and short-lived postoperative adverse effects. These include purpura and temporary pigment changes, with blistering, crusting, skin texture changes and scarring occasionally occurring.