Optical glass is a type of glass with distinctive design and process features to have precise optical properties. For example, some exceptional features include refractive index, dispersion, transmission, and homogeneity.
Therefore, many applications rely on the manipulation of light and therefore take advantage of optical glass in some form. Spectroscopy, laser tuning and calibration, quantum computing, magnetometer cells, and atomic clocks are just a few. Here, we will explore what optical glass is and why it is important. We will also learn what it is for, its benefits, and the components that require it.
The Optical Glass Difference
Shop NowOptical glass is specifically designed for use in optical applications. Simply put, the basic element of an optical system is light. Therefore, the traditional practical applications of optics are found in a variety of technologies and everyday objects. These include mirrors, lenses, telescopes, microscopes, lasers, and fiber optics.
However, many modern optical systems find applications in sensing, recording, storage, and transmission of data. These applications stimulate the development of new optical devices, components, materials, and applied technologies.
For this reason, optical glass with its high-purity materials and incredibly low levels of contaminates, is extremely transparent to light. It is also very resistant to scratching and breaking, which makes it ideal for use in high-precision optical instruments.
Unique Defining Parameters
Traditional glass is a non-crystalline solid material that is made of silica (SiO2) and other additives. These can include metal oxides, borates, or phosphates. As such, it can be shaped into various forms by melting, blowing, molding, or drawing. It can also be modified by coating, etching, or doping to change its surface or internal properties.
Optical glass takes full advantage of these characteristics. It is defined by its optical parameters, such as:
- Refractive index (n): The ratio of the speed of light in a vacuum to the speed of light in the glass at a given wavelength. The refractive index determines how much the light bends when it passes through the glass.
- Abbe number (V): A measure of the dispersion or variation of the refractive index with wavelength. The Abbe number quantifies the amount of chromatic aberration or color distortion caused by the glass.
- Transmission (T): The percentage of light that passes through the glass without being absorbed or reflected. The transmission depends on the wavelength of the light and the thickness and purity of the glass.
- Homogeneity (H): The degree of uniformity of the refractive index throughout the glass. Homogeneity affects the image quality and resolution of the optical system.
Common Classifications
Optical glass is usually classified into diverse types or families based on its refractive index and Abbe number. Some common types of optical glass are:
- BK7: A borosilicate crown glass with n = 1.5168 and V = 64.17. It is one of the most widely used optical glasses for general-purpose applications.
- F2: A flint glass with n = 1.6200 and V = 36.37. It has high dispersion and low transmission in the ultraviolet range.
- SF10: A dense flint glass with n = 1.7280 and V = 28.46. It has a very high refractive index and a very low Abbe number.
- LAFN7: A lanthanum flint glass with n = 1.7495 and V = 34.95. It has a high refractive index and low dispersion due to the addition of lanthanum oxide.
- N-LASF45: A lead lanthanum flint glass with n = 1.8040 and V = 35.06. It has an extremely high refractive index. It also has an exceptionally low transmission in the visible range due to the addition of lead oxide.
Thermal Properties
Shop NowOptical glass can also be categorized by its thermal properties, such as:
- Coefficient of thermal expansion (CTE): The rate of change of the volume or length of the glass with temperature. CTE affects the stability and alignment of the optical system under varying temperatures.
- Transformation temperature (Tg): The temperature at which the glass changes from a rigid solid to a viscous liquid. The Tg determines the processing temperature and annealing conditions of the glass.
- Softening temperature (Ts): The temperature at which the glass becomes soft enough to deform under its own weight. The Ts determines the molding temperature and shape retention of the glass.
Some examples of optical glasses with different thermal properties are:
- N-BK7HT: High homogeneity version of BK7 with CTE = 7.1 x 10^-6 K^-1^ , Tg = 557 °C and Ts = 719 °C.
- N-FK51A: Low dispersion flint glass with CTE = 5.9 x 10^-6 K^-1^ , Tg = 472 °C and Ts = 593 °C.
- N-LASF44: A lead lanthanum flint glass with CTE = 10.8 x 10^-6 K^-1^ , Tg = 557 °C and Ts = 732 °C.
Why Is Optical Glass Important?
Optical glass is important because it enables the creation of optical devices and systems that manipulate light. These forms of light manipulation include:
- Focusing: Optical glass can make lenses that converge or diverge light rays to form images or beams.
- Reflecting: In this case, special glass mirrors bounce back light rays with the same angle and direction as incident rays.
- Refracting: Optical glass can be used to make prisms that bend or split light rays. As a result of prism properties, it does so by different angles depending on wavelength or polarization.
- Filtering: Filters of optical glass transmit or block light rays depending on their wavelength, intensity, or polarization.
- Amplifying: Lasers make use of optical glass to generate coherent and monochromatic light beams. As a result, these stimulate the emission of photons from the atoms or molecules in the glass.
- Modulating: Modulators of optical glass alter the amplitude, phase, frequency, or polarization of light beams. They do so by applying electric, magnetic, acoustic, or thermal fields to the glass.
Advantages Over Other Materials
Optical glass is also important because it has many advantages over other materials, such as:
- Versatility: Optical glass can be shaped into various forms and sizes by different methods. For example, these include melting, blowing, molding, drawing, grinding, polishing, coating, etching, or doping.
- Purity: Optical glass has extremely high material purity and low amounts of bubbles and inclusions. This improves its optical quality and performance.
- Homogeneity: Annealing achieves a precisely defined and uniform refractive index throughout the glass. This reduces optical aberrations and distortions.
- Transparency: Optical glass can have high light transmission over a wide range of wavelengths, from ultraviolet to infrared. Of course, this depends on its composition and coating.
- Durability: Optical glass can have high mechanical strength and resistance to thermal shock, chemical corrosion, and radiation damage. The amount depends on its additives and treatment.
Essential for Optical Instruments
Shop NowAs we have established, optical glass is specifically designed for use in optical applications. Due to its high-purity materials and exceptionally low levels of impurities, it is transparent to light. Plus, it is also very resistant to scratching and breaking, making it ideal for use in high-precision optical instruments.
You find this exceptional material in a wide variety of optical instruments for good reason. From spectroscopes to lasers, a variety of extreme applications such as gas sensing, quantum computing, atomic clocks, and more benefit.
In lasers, optical glass is used to form the laser cavities that allow them to generate coherent light. Whereas with gas sensing devices, optical glass forms the windows and filters that allow gases to be detected. However, in quantum computing devices, optical glass is used to trap and control atoms and photons. While in atomic clocks, optical glass is used to form the cavities that keep time with extreme accuracy.
According to Popular Mechanics magazine: “The exquisitely precise timekeeping of atomic clocks is used for measuring time and distance for everything from our Global Positioning System (GPS), online communications across the world, fractions of a second in trading stocks, and timed races in the Olympics. But scientists have developed even more advanced atomic clocks that could reveal more about the mysterious parts of the universe—like dark matter—than we have ever seen.”
A Deeper Dive Into Uses of Optical Glass
Optical glass serves a variety of applications that involve the manipulation of light for scientific, industrial, medical, or artistic purposes. Some examples of these applications are:
Laser Spectroscopy
Optical glass helps make components such as lenses, prisms, mirrors, filters, and gratings to generate, direct, analyze, and measure the spectra of light emitted or absorbed by atoms or molecules. Laser spectroscopy aids in the study of the structure and dynamics of matter. It does so by identifying chemical elements and compounds, detecting trace gases and pollutants, measuring temperature and pressure, and performing imaging and sensing.
Laser Locking
Optical glass makes up many diverse components such as reference cells, vapor cells, alkali vapor cells, and rubidium cells. These often help stabilize the frequency and wavelength of lasers by locking them to a specific atomic transition. Laser locking improves the accuracy and precision of lasers for applications such as metrology, communication, navigation, and synchronization.
Laser Tuning
Optical glass is used to make components such as etalons, acousto-optic modulators and electro-optic modulators that are used to adjust the frequency and wavelength of lasers by changing the optical path length or refractive index of the glass. Laser tuning is used for changing the output characteristics of lasers for applications such as spectroscopy, microscopy, surgery and entertainment.
Laser Calibration
Reference cells, vapor cells, alkali vapor cells, and cesium cells of optical glass help calibrate the frequency and wavelength of lasers by comparing them with a known atomic standard. Laser calibration ensures the reliability and consistency of lasers for applications such as metrology, communication, navigation, and synchronization.
Gas Sensing
Optical glass comprises components such as laser cells, vapor cells, alkali vapor cells, and reference cells. These detect and measure the concentration and pressure of gases by analyzing the absorption or emission spectra of light passing through the gas-filled glass. Gas sensing monitors the quality and safety of air, water, and soil, detecting leaks and explosions, controlling combustion processes, and measuring biological functions.
Quantum Computing
Components such as quantum dots, photonic crystals, and optical cavities come from optical glass. These elements help manipulate quantum states of light for performing quantum information processing. Quantum computing helps solve complex problems that are beyond the capabilities of classical computers, such as cryptography, optimization, simulation, and machine learning.
Magneto-Optical Traps
Optical glass can be used to create highly divergent conical MOT trapping beams by using millimeter ball lenses. These lenses are contained within a metal cube and create a large trapping volume with low laser power requirements. Optical glass also makes the glass cell that contains the MOT and the magnetic trap. The glass cell has a clear optical access region. Plus, it is often surrounded by coils that generate the required magnetic field. Optical glass is important for MOTs because it allows for precise manipulation and observation of cold, neutral atoms that can be used for experiments in quantum physics.
A Look At Optical Glass Components
Shop NowLet’s take a closer look at a few of the components manufactured by Precision Glassblowing and how we optimize and take advantage of these unique properties.
The purity level of the natural elements used in manufacturing all vapor cells is greater than 99% and is then distilled to an even higher purity during the filling process. Upon request, Precision Glassblowing offers gases like Helium, Neon, Argon, Krypton, Xenon, Nitrogen, and Ethane as well as paraffin coating and OTS coating (additional charges may apply).
All vapor cells are helium leak checked and then baked under vacuum to the 10-8 Torr range for a minimum of 24 hours before they are filled with the selected element.
If ordering multiple cells, please contact customer service for discounts.
Laser Cells
Laser cells are vessels that contain a gas or vapor critical to the performance of a laser. The walls of laser cells are typically made of optical glass to allow the laser light to pass through them without being absorbed or scattered.
Reference Cells
Reference cells are vessels that contain a gas or vapor that is used to calibrate other optical instruments. Of course, reference cells also allow the light from the instrument to pass through them without being absorbed or scattered due to the use of this uniquely refined glass. Precision Glassblowing specializes in a variety of vapor cells.
More about Vapor Cells
Vapor cells are vessels that contain the vapor of an alkali metal, such as rubidium or cesium. These cells are in atomic clocks and other devices that require high-precision measurements of time. Walls of optical glass allow the light from an atomic clock to pass through them without being absorbed or scattered. Some examples include:
Rubidium Cells – Rubidium cells are vessels that contain the vapor of rubidium.
Cesium Cells – Cesium cells are vessels that contain the vapor of cesium.
Potassium Cells – Potassium cells are vessels that contain vapor of potassium and are also present in atomic clocks.
Sodium Cells – Sodium cells are vessels that contain vapor of sodium. These are in pacemakers and other devices that require high-precision measurements of time. Like their counterparts, the walls of sodium cells are of optical glass.
The Future of Optical Glass
Shop NowThe demand for optical glass continues to grow as new, progressive instruments emerge. Innovative applications, such as quantum computing and atomic clocks, are already increasing the demand for optical glass exponentially.
Precision Glassblowing has been manufacturing scientific glassware since 1982. From our humble beginnings, we grew to a staff of 35 glassblowers with a combined professional glassblowing experience exceeding 400 years. Honesty, integrity, and great customer service are the foundations of our company.
In 2009, following their merger, Technical Glass Inc., pioneers in the development of glass cells for cold atom physics, and Precision Glassblowing, set about opening their Optical Division. Tech Glass brought years of research and development to complement Precision’s production capabilities. Together, as one company, we continue to explore and expand the boundaries of scientific glass.
For questions or quotes contact Jay: Meikrantz@