Modular Multi-Port Integrating Spheres

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4P4 Sphere Major Design Features

Features

• Ø100 mm Inner Diameter in Modular, Cuboctahedral Housing
• Pre-Configured and Custom-Configured Integrating Spheres
• 3 or 4 Modular Faces with Interchangeable Port Inserts
  • Inserts Offered Are Ø14 mm Dual Ports, Ø1" Port, Ø2" Port, or Port Plug
• Up to 8 Ø5 mm Ports with SM1 Threading
  • Directly Connect Our SM1 Photodiodes (See Table to the Right)
  • Mount Fiber-Coupled Light Sources using SM1 Fiber Adapters
• Durable, White, Highly Reflective Sphere Material
• Operating Range: 250 - 2500 nm (Unless Limited by the Detector)
• Universal 8-32 / M4 Tap on Side Panels for Rail System (Included with Stock Items) or Mounting to Ø1" Posts

Thorlabs' Modular Integrating Spheres each provide a durable, highly reflective surface to optimally diffuse light. The sphere is constructed inside a cuboctahedral (fourteen-sided) housing that can be configured for a wide variety of applications. Each of the eight triangular faces can support a Ø5 mm port with SM1 internal threads, enabling easy mounting of our mounted photodiodes or fiber-coupled components such as LEDs or spectrometers (SM1 adapters may be needed). Either three or four of the square faces can be configured with inserts selected by the user as described in the Modularity section below. The two faces that are not modular provide a universal 8-32 / M4 tapped hole, allowing mounting to the 25 mm rail system stand (included with stock items) or a Ø1" post. These integrating spheres are available from stock as one of two pre-set configurations or ordered as a custom configuration using the tool below.

The spheres are manufactured from PTFE-based bulk material that has high reflectance in the 250 - 2500 nm wavelength range (see Specs tab) and is resistant to heat, humidity, and high levels of radiation. This reflective surface is designed to have specific roughness and diffusive reflection properties and should not be cleaned using solvents, as this could damage the inner surface. We only recommend using compressed air for cleaning the inner surfaces of the integrating spheres.

Integrating spheres enable high sensitivity measurements of optical signals in a variety of setups. An integrating sphere causes the incoming radiation to undergo multiple reflections over the sphere surface, which diffuses and depolarizes the light beam. This makes it the ideal instrument for many applications such as laser power, flux, reflectance and radiance measurements, as well as creating a uniform light source for camera calibration.

Modularity
These integrating spheres come with either three or four modular faces. Each modular face accepts one of four interchangeable Port Inserts, available below with a variety of port sizes, SM threading options, and tapped holes for cage system compatibility. Spheres available from stock are pre-configured for common applications and include a preset selection of port inserts and two fixed Ø5 mm ports. Custom-configured spheres allow the user to choose the inserts and up to eight fixed Ø5 mm ports.

Any of the inserts in the modular faces can be swapped for other interchangeable port inserts, including additional inserts sold separately below. The inserts are each fastened by two M3 screws; to exchange the included inserts with other inserts, loosen the screws using a 2 mm (5/64") hex key or balldriver. Custom inserts may be available for applications not served by the inserts available from stock. Contact Tech Support for more information.

Calibration
Thorlabs can calibrate integrating spheres with user-selected sensors upon request and provide the pertinent NIST- and/or PTB-traceable certificates of calibration. Contact Tech Support for more information.

Ultraviolet and Blue Fluorescence Emitted by Integrating Spheres

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Typical yields at each wavelength are around four orders of magnitude lower than the excitation wavelength. [4]

The spectral fluorescence yield relates the intensity of the fluorescence emitted within the integrating sphere with the intensity of the excitation wavelength. The yield is calculated by dividing the wavelength-dependent, total fluorescence excited over the entire interior surface of the sphere by the intensity of the light excitation.

Data were kindly provided by Dr. Ping-Shine Shaw, Physics Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.

A material of choice for coating the light-diffusing cavities of integrating spheres is polytetrafluoroethylene (PTFE). This material, which is white in appearance, is favored for reasons including its high, flat reflectance over a wide range of wavelengths (see the Specs tab for details) and chemical inertness. However, it should be noted that integrating spheres coated with PTFE emit low levels of ultraviolet (UV) and blue fluorescence when irradiated by UV light. Spheres coated with barium sulfate, which is an alternative coating with lower reflectance, also fluoresce in this wavelength range. [1-3]

Hydrocarbons in the Coatings Fluoresce
It is not the PTFE or barium sulfate that fluoresces. The sources of the UV and blue fluorescence are hydrocarbons in the coating. Low levels of hydrocarbon impurities are present in the raw coating material, and pollution sources deposit additional hydrocarbon contaminants in the coating material of the integrating sphere during its use and storage. [1]

Fluorescence Wavelength Bands and Strength
Researchers at the National Institute of Standards and Technology (NIST) have investigated the fluorescence excited by illuminating PTFE-coated integrating spheres. The total fluorescence output by the integrating sphere was measured with respect to fluorescence wavelength and excitation wavelength. The maximum fluorescence was approximately four orders of magnitude lower than the intensity of the exciting radiation.

The UV and blue fluorescence from PTFE is primarily excited by incident wavelengths in a 200 nm to 300 nm absorption band. The fluorescence is emitted in the 250 nm to 400 nm wavelength range, as shown by the figure to the right. These data indicate that increasing the excitation wavelength decreases the fluorescence emitted at lower wavelengths and changes the shape of the fluorescence spectrum.

As the levels of hydrocarbon contaminants in the PTFE increase, fluorescence increases. A related effect is a decrease of the light output by the integrating sphere over the absorption band wavelengths, due to more light from this spectral region being absorbed. [1, 3]

Impact on Applications
The UV and blue fluorescence from the PTFE has negligible effect on many applications, since the intensity of the fluorescence is low and primarily excited by incident wavelengths <300 nm. Applications sensitive to this fluorescence include long-term measurements of UV radiation throughput, UV source calibration, establishing UV reflectance standards, and performing some UV remote sensing tasks. [1]

Minimizing Fluorescence Effects
Minimizing and stabilizing the fluorescence levels requires isolating the integrating sphere from all sources of hydrocarbons, including gasoline- and diesel-burning engine exhaust and organic solvents, such as naphthalene and toluene. It should be noted that, while hydrocarbon contamination can be minimized and reduced, it cannot be eliminated. [1]

Since the history of each integrating sphere's exposure to hydrocarbon contaminants is unique, it is not possible to predict the response of a particular sphere to incident radiation. When an application is negatively impacted by the fluorescence, calibration of the integrating sphere is recommended. In [4], the authors describe a calibration procedure that requires a light source with a well-known spectrum that extends across the wavelength region of interest, such as a deuterium lamp or synchrotron radiation, a monochromator, a detector, and the integrating sphere.

References
[1] Ping-Shine Shaw, Zhigang Li, Uwe Arp, and Keith R. Lykke, "Ultraviolet characterization of integrating spheres," Appl.Opt. 46, 5119-5128 (2007).
[2] Jan Valenta, "Photoluminescence of the integrating sphere walls, its influence on the absolute quantum yield measurements and correction methods," AIP Advances 8, 102123 (2018).
[3] Robert D. Saunders and William R. Ott, "Spectral irradiance measurements: effect of UV-produced fluorescence in integrating spheres," Appl. Opt. 15, 827-828 (1976).
[4] Ping-Shine Shaw, Uwe Arp, and Keith R. Lykke, "Measurement of the ultraviolet-induced fluorescence yield from integrating spheres," Metrologia 46, S191 - S196 (2009).