Alexandrite

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Alexandrite (Cr3+:BeAl2O4, chromium-doped beryllium aluminate) is a laser gain material used in solid-state lasers for applications such as dermatology and Lidar, etc. Alexandrite is produced via the Czochralski growth method. It has a thermal shock resistance five times that of Nd:YAG and a wide emission wavelengths typically between 710nm and 800nm – in many cases around 755nm. It is possible to make broadly wavelength-tunable lasers based on alexandrite. Alexandrite is anisotropic, the absorption and gain properties strongly depend on the direction of pump light’s polarization. This together with the strong birefringence of the material makes it easy to obtain linearly polarized emission with low depolarization losses.

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Product Specifications Physical & Optical Properties Product Features & Applications

Product Specifications

Dimension Tolerance	*Diameter (+0/-0.05) Length (+1/-0.5) mm**
Scratch/Dig	10/5	Perpendicularity	< 5'
Parallelism	< 30"	Chips	< 0.1mm
Flatness	< λ/10 @ 633nm	Clear Aperture	≥ 98%
Wavefront	< λ/2 per inch @ 633nm	Dopant	0.1% - 0.2%
Coating	Option 1 - Normal: AR/AR755nm
Coating	Option 2 - Mirror coating: HR/PR755nm
Damage Threshold	> 1.5 Million pulses (tested by third party)

Standard Products

Part Number	Size	Working Wavelength
1.CR.ALX.D95311.C003	φ9.53X116.8	755nm
1.CR.ALX.D08130.C004	φ8X130	755nm
1.CR.ALX.D07127.C002	φ7X127	755nm
1.CR.ALX.D07125.C002	φ7X125	755nm
1.CR.ALX.D07110.C004	φ7X110	755nm
1.CR.ALX.D63512.C003	φ6.35X120	755nm
1.CR.ALX.D63511.C007	φ6.35X115	755nm
1.CR.ALX.D63510.C002	φ6.35X105	755nm

Physical Specifications

Formula:	Cr³⁺: BeAl₂O₄
Crystal Structure:	Orthorhombic
Unit Cell Dimensions (Å)	5.476(a), 9.404(b), 4.427(c)
Thermal Expansion (x 10^-6∙K^-1):	5.9(a), 6.1(b), 6.7(c)
Refractive Index (at 750 nm):	1.7367(a), 1.7241(b), 1.7346(c)
Melting Point (°C):	1870
Mohs Hardness:	8.5
Density (g/cm³):	3.7
Thermal Conductivity(W∙cm^-1∙K^-1):	0.23
Thermal Shock Resistance (W∙cm^-1):	35 - 74
dn/dT (K^-1):	8x10^-6
Lasing Wavelength	710-800nm

Absorption Spectrum

Description

Alexandrite is a 4-energy level laser gain material used in solid-state lasers for applications such as dermatology and Lidar, etc. Alexandrite crystal is grown and produced in monocrystalline form with high crystal quality, using Czochralski growth method. Its Emission wavelengths are typically between 710nm and 800nm. It is possible to make broadly wavelength-tunable lasers based on alexandrite. In most cases, it is operated at wavelength 755nm, where the maximum laser gain can be achieved.

Alexandrite is anisotropic, the absorption and gain properties strongly depend on the direction of pump light’s polarization. This together with the strong birefringence of the material makes it easy to obtain linearly polarized emission with low depolarization losses.

Alexandrite has a thermal shock resistance five times that of Nd:YAG, due to its particularly high mechanical and thermo-mechanical strength of the material and its thermo-optical properties. It can not only tolerate elevated temperatures, but may even work better there. As a result, pulsed alexandrite lasers often work better with elevated temperatures of the laser crystal. Very high pump powers can be applied to the flash lamps. Pump pulse energies are typically of the order of hundreds of joules or several kilojoules, and the pulse repetition rate is normally quite low

The most important application area of alexandrite lasers is dermatology. For example, such lasers are used for hair removal, for removing tattoos and for treating visible leg veins and pigmented lesions. In the case of hair removal, the light from a long-pulse laser is preferentially absorbed in the hair shafts, and the resulting heat damages these hair shafts and the surrounding hair follicles (selective photothermolysis). By cooling the skin during the treatment, damage to the epidermis is minimized. The short emission wavelength of an alexandrite laser, compared with that of a Nd:YAG laser, is beneficial for removing finer hairs, but increases the risk of skin damage in the case of darker skin. (The absorption occurs mostly in melanin, which occurs in hair but also in dark skin, and less in hemoglobin.)

In dermatological applications, high intensity pulses from a free-running laser are normally applied to large areas of skin. The high pulse energy and average power allow for a reasonably short treatment time. Due to the large beam area, there are no special requirements on beam quality. This means that relatively simple lasers can be used for such purposes.

Applications

·Dermatology

·Spectroscopy

·Atmospheric lidar etc.

·Long Pulse, Q-switched or Picosecond 755nm Lasers

Our Advantages

·Crystal Boules growth, cutting, polishing, coating all in house

·Rod: diameter 3mm to 10mm, length up to 153mm

·Flat or Curved ends

·High damage threshold coating

·Excellent quality, competitive price, fast delivery, good service