Introduction:

Single Synthetic Crystal Quartz is grown by hydrothermal method in autoclaves. It has trigonal crystal structure with right-handed or left-handed modification. Quartz crystals have low stress birefringence and high refractive index homogeneity. The optical transmission range of crystal quartz is 0.15-4 microns. Due to its piezoelectric properties, low thermal expansion, good mechanical parameters and excellent optical characteristics, cultured quartz is used in electronics, precision and laser optics, optical fibre communications, X-ray optics, and pressure sensors, ect..

Quartz crystal of this grade is used for applications that need excellent optical characteristics and large size ingot to produce optical filters, windows, prisms etc.. Usually it is specified by inclusion and homogeneity. This material is mostly grown along the C-axis. Quartz crystals with inclusion specifications of Ia and Ib grade(IEC) is available in BCT.

Refractive indexs of cultured quartz:

For more than 30 years quartz crystals growth history and creativity, BCT is the leading manufacturer of large size and low inclusions crystal quartz in China.

Specifications:

• Size: Z: max 135mm, X: 150mm, Y: 240-280mm
• Inclusions: IEC grade I
• Q-value: >2.40 million.
• Homogeneity: 1*10^-5

Applications:

For special customers who need large size and high optical quality quartz crystal ingot to produce elements as follows

• Optical filters
• Windows
• Prisms
• Rotators
• Waveplates
  
  

Related technologies

Quartz

The technical formula of crystal quartz is SiO₂ and it is composed of two elements, silicon and oxygen. In its amorphous form SiO₂ is the major constituent in many rocks and sand. The crystalline form of SiO₂ or quartz is relatively abundant in nature, but in the highly pure form required for the manufacture of quartz crystal units, the supply tends to be small.

                         Autoclave, the quartz growing equipment

The limited supply and the high cost of natural quartz have resulted in the development of a synthetic quartz manufacturing industry. Synthetic quartz crystals are produced in vertical autoclaves. The autoclave works on the principle of hydrothermal gradients with temperatures in excess of 400 °C and pressures exceeding 1,000 atmospheres. Seed quartz crystals are placed in the upper chamber of the autoclave with natural quartz being placed in the lower chamber. An alkaline solution is then introduced which when heated increases the pressure within the chamber. The autoclave heaters produce a lower temperature at the top chamber in comparison to the bottom. This temperature gradient produces convection of the alkaline solution that dissolves the natural quartz at the bottom of the chamber and deposits it on the seed crystals at the top. Alpha crystals produced by this method can have masses of several hundred grams and can be grown in a few weeks. If the temperature reaches 573 °C a phase transition takes place that changes the quartz from an alpha to a beta (loss of piezoelectric property).

The process continues until the growing crystals reach their desired size. The process normally take 30 to 60 days for a other types of crystal, at least one producer has made runs of about 180 days for large size that clients desired. The cultured crystals can be custom grown with specific properties.

The processing of quartz crystal for various end uses is the same whether natural or cultured seed crystal is used. However, producers must avoid seed crystals with defects that would pass crystal on to new generations of cultured crystal. Natural quartz crystal is preferred as seed material to ensure that genetic defects will not be repeated in the succeeding generations.

Once produced, cultured crystals are examined for physical elements defects before cutting. They are then cut, usually with diamond or slurry saws, along a predetermined crystallographic plane to a thickness slightly larger than that desired. Each wafer is inspected and diced into blanks of the desired dimensions. The blanks then progress through a series of lapping stages until they reach the final thickness.

Quartz crystals are an indispensable component of modern electronic technology. They are used to generate frequencies to control and manage virtually all communication systems. They provide the isochronous element in most clocks, watches, computers and microprocessors. The quartz crystal is the product of the phenomenon of piezo-electricitydiscovered by the Curie brothers in France in 1880.

Most optical applications use quartz in the fused form as silica glass. Relatively small quantities of cultured quartz crystal are used directly for special optical considerations Quartz crystal also has uses involving normally polarized laser beams, Brewster windows and prisms, birefringent filters.

Since the interaction of biomolecules with UV-light is one of the most frequently employed analytical methods in the field of biochemistry, UV-transparent materials, such as quartz, are often demanded by biotechnical applications. The transparency of the material can also be important for fluid or particle handling systems where visual observation of the system’s interior is of interest.

Cultured quartz crystal production is concentrated in China, Japan, Russia and the United States with several companies producing crystal in each country. Smaller production capacity exists in Belgium, Brazil, Bulgaria, France, Germany, South Africa, and the United Kingdom.

Quartz Crystalline Properties

Transmission Range   0.150-4.0 µm and 50-1000 µm   Refractive Index   no = 1.5350, ne = 1.5438 @ 1 µm   Reflective Loss   8.2% @ 2 µm  Reststrahlen   Density   2.65 g/cm3   Melting Point   1710°C, 1657°C   Molecular Weight   60.06  Thermal_Conductivity   || C: 11.7 W/(m·K) @ 20°C; ^C: 6.5  Specific Heat   744 J/(kg·K)   Thermal Expansion   || C: 7.97 x 10-6 /°C ; ^C: 13.37 x 10-6 /°C @ 0°-80°C  Hardness (Mohs)   740 (Indenter load 500g)   Young`s Modulus   || C: 97; ^C: 76.5 GPa @ 25°C   Shear Modulus   44 GPa  Bulk Modulus   98 GPa   Rupture Modulus   41 MPa   Elastic Coefficient   C11 = 86.6; C12 = 6.7; C13 = 12.4; C14 = 17.8; C33= 106.4; C44 = 58 GPa   Dielectric Constant   || C: 4.27 @ 30 MHz @ 25°C; ^C: 4.34  Solubility in Water   insoluble  Type of Material   Single crystal, synthetic   Crystal Structure   trigonal, point group 32, a = 4.9138 Å, c = 5.4052 Å  Cleavage Planes   Common Diameter   Plates (blank) 120 mm (y) x 90 mm (x) x 27 mm (z)  Application   polarizing optics, piezoelectric components, VUV filter, FIR windows  Remarks   dextrorotatory Quartz is common, max. temperature for application > 1200°C, chemical constant, will be damaged by contact with HF and hot concentrated alkalines

Windows

The minimum thickness of the crystal quartz windows was chosen to withstand a pressure difference of 4 atmospheres, i.e., with a safety factor of 4. Formulas for the stress in loaded circular plates with clamped and free rims are given in handbooks. The tensile strength of z-cut crystal quartz was taken as 5400 PSI. Following figure gives the minimum quartz thickness required to achieve a 4-atmospheres bursting pressure, as a function of the clear aperture, with clamped and free rims. Because the window clamping arrangement is always somewhat flexible, it is safest to assume a free rim and use the thicker quartz as required.

For the windows, having a diameter at the O-ring of approximately 4″, 0.225″ was chosen as the minimum thickness for the quartz crystal, based on the following figure. The thickness was then increased using the MMICAD model as a guide to optimize the multilayer window.

Figure. Minimum thickness of crystal quartz required to achieve a 4-atmospheres bursting pressure.

Prisms

Prisms are blocks of optical quartz crystals with flat polished sides arranged at precisely controlled angles to each other, which deflect, deviate and rotate beams of light as well as dispersing their wavelengths.

There are many types of custom-built optical prisms, each having a particular geometry to achieve the reflections necessary to perform a specific imaging task. Reflecting prisms may invert, rotate, deviate or displace a beam. Dispersing prisms produce spectral separation for spectroscopic applications or for tuning a laser output.

Most of prisms are widely used for laser and commercial applications; hereby it briefly is described some applications of prisms to illustrate the versatility of this optics:

• Prism spectrometers;

• Beam turning;

• Beam steering;

• Laser tuning;

• Evanescent wave coupling;

• Prisms as beam expanders.

Rotators

Quartz rotators are designed for use at a specified single wavelength at normal incidence and are anti-reflection coated using specially developed processes to achieve high laser damage threshold.

Their principle of operation relies on the inherent optical activity (otherwise known as circular birefringence) of crystalline quartz. It is a similar mechanism to the well known linear birefringence of quartz used in waveplates, but applies when light is transmitted parallel to the optic axis. The incident linear polarized light is split into two equal components of left and right circularly polarized light. Each component co-propagates through the crystal quartz but is subject to a slightly different refractive index which delays one component with respect to the other. At the exit face the two components recombine to obtain linear polarization whose orientation with respect to the input face is dependent solely on the wavelength of the light and thickness of the crystal quartz.

Optical quartz rotators should be used at normal incidence. If used off-axis, linear birefringence effects quickly dominate producing unwanted elliptically polarized output beams.

Waveplates

Over the years, these wave plates have gotten thinner and smaller in size in response to the trend of utilizing shorter wavelengths within the visible range. New, high-powered lasers are being utilized in increasingly smaller areas or spot sizes to meet the performance requirements of more demanding consumer electronics.

Quarter Waveplates

Quarter waveplates add l/4 of retardance making them useful for converting linearly polarized light into circularly polarized light. Conversely, they will convert circularly polarized light back to linear. Combined with a linear polarizer, quarter waveplates can be used as an isolator to reject back reflections.

Half Waveplates

Half waveplates introduce a retardance of l/2 which makes them useful for rotating the polarization state of an input. A linearly polarized input will produce a linear output rotated by 2q (where q is the angle between the input polarization and the waveplate fast axis).

Zero Order Waveplates

Zero order waveplates are constructed by combining two multi-order quartz waveplates with a thickness difference of exactly l/4 (or l/2) retardance. Aligning the fast axis of one plate to the slow axis of the other, and thereby cancelling the bulk multiorder retardance, results in a zero order performance waveplate. The zero order waveplates offer substantially lower dependence on temperature and wavelength. Zero order waveplates are constructed with a precision air gap and are AR coated for maximum transmission making them ideal for high power laser applications. Multi-order waveplates are also offered for applications less sensitive to temperature and wavelength changes.