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Technical Overview of Alexandrite Crystal Rods

Product Name: Alexandrite crystal rod
Simplified chemical formula : Cr: BeAl₂O₄
Material composition: Crystalline material (main components: oxygen 50.36%, aluminum 42.40%, beryllium 7.08%, chromium 0.16%)
Product images :
Alexandrite crystal rods

I. Product Introduction :
Alexandrite crystal rods are made from chromium-doped beryllium aluminate crystals with the simplified chemical formula Cr : BeAl2O4. Beryllium aluminate ( BeAl2O4 ) belongs to the orthorhombic crystal system and is a laser gain medium with excellent optical properties , exhibiting good physical stability and optical homogeneity. This crystal uses beryllium aluminate (BeAl2O4) as the matrix and incorporates trivalent chromium (Cr3+) ions as activating ions to form an energy level structure suitable for laser emission. Alexandrite crystal rods are commonly used to generate 755nm wavelength lasers, and this product is ideally suited for manufacturing laser hair removal devices and lasers used for skin pigmentation treatment.

Alexandrite crystal rods are produced by machining and polishing chromium-doped beryllium aluminate crystal blanks into rod shapes that meet customer requirements. First, raw materials BeO, Al2O3, and the dopant Cr2O3 are melted in a high-temperature growth furnace under a specific atmosphere, and crystallization is controlled using the Czochralski method. Through a high-temperature chemical reaction, a chromium-doped beryllium aluminate crystal blank is obtained. Elemental beryllium exists in a stable and inseparable form within the crystal. After obtaining the chromium-doped beryllium aluminate crystal blank, the crystal is machined into a rod shape, and the light-transmitting surface of the crystal is polished to an optical-grade finish. Sometimes, an optical film may be deposited on the light-transmitting surface of the crystal to meet the reflection and transmission requirements of the laser resonator .

Working principle-How can Alexandrite crystal rod be used for cosmetic laser treatment:

Alexandrite crystal rods (Cr:BeAl2O4) are used in the manufacture of lasers. These crystal rods function as pump-driven laser emission components. Their specific working principle is as follows:

In a laser system , the optical pump (such as a xenon lamp or laser diode) acts on a Cr:BeAl2O4 crystal rod. The trivalent chromium ions ( Cr3+) in the Cr:BeAl2O4 crystal rod act as activating ions, achieving population inversion. The crystal rod generates a laser with a wavelength of 755 nm through stimulated emission .
This product, as a laser gain medium, is placed in an optical resonant cavity inside the laser. The laser radiation generated from the crystal will continuously increase as it travels back and forth in the resonant cavity, and after coupling through the output mirror in the laser, a stable 755 nm laser output is finally formed .

755nm wavelength laser light can be effectively absorbed by melanin , therefore lasers made with this product are commonly used in laser hair removal or skin pigmentation treatment.

When a 755nm laser shines on the skin, the light energy is rapidly absorbed by the melanin in the hair follicles or the pigment particles in pigmented lesions.
The absorbed light energy is converted into heat energy in a very short time, generating instantaneous local high temperature .
For laser hair removal : The heat generated precisely destroys the hair follicle's germinal structure, thereby permanently inhibiting hair growth ;

For the treatment of skin pigmentation: Heat will break down pigment particles (such as melanosomes or tattoo ink particles) into smaller fragments , thereby gradually fading and eliminating pigmented lesions.

3. Production process:
( 1) Crystal blank growth : Using the Czochralski method, raw materials BeO, Al2O3, and dopant Cr2O3 are added to a high-temperature growth furnace under a specific atmosphere. The furnace temperature is raised to approximately 1870°C, melting the raw materials into a melt. A seed crystal rod is used within the melt to control the pulling speed, rotation rate, and heating power , thereby crystallizing and growing a chromium-doped beryllium aluminate blank. Elemental beryllium exists in a stable, inseparable form within the crystal.
( 2) Preliminary processing: Non-destructive testing is performed on the crystal blank. After confirming that it meets the standards , it is cut, oriented and rough ground according to the design dimensions to process the crystal blank into a rod shape.
( 3) Further processing: Through milling, fine grinding and polishing processes, ensure that the crystal rod meets the specified geometric tolerances and surface accuracy, and meets the requirements of optical grade.
( 4) Surface treatment: Depending on the design requirements of the laser resonator, an anti-reflection film or a high-reflection film may sometimes be deposited on the light-transmitting surface of the chromium-doped beryllium aluminate crystal rod to optimize the laser output efficiency and spectral characteristics.

4. Application areas:

In the field of medical aesthetics: used in the manufacture of 755 nm laser hair removal devices, tattoo removal equipment, skin pigmentation treatment devices, etc.
Industrial testing: Laser light sources suitable for some material analysis and non-destructive testing systems.

Tags: Alexandrite crystal rods