Optics for the Visible Spectrum
Wavelength range: 400 – 700nm
The visible wavelength region of the electromagnetic spectrum is a relatively narrow band (for our purposes covering a wavelength range of 400 – 700 nanometers) defined by the sensitivity of the human eye. Nineteenth-century demand for visual instrumentation including microscopes and telescopes formed the foundation of the optics industry and led to the development of optical component manufacturing techniques still in widespread use today. It should not surprise us therefore that many optical systems utilize the visible portion of the spectrum.
Instruments such as sighting systems and cameras rely on the faithful reproduction of color through broadband white light imaging. The important field of analytical instrumentation uses spectroscopic techniques to determine the presence of various substances by examination of their visible spectra. Reprographic equipment, which has revolutionized the printing industry, uses visible optics predominantly in the green region but the use of shorter blue wavelengths provides finer resolution. Barcode scanning uses red light to read the UPS labels printed on product packaging. Alignment of machinery and precise measurement of a position are other applications which use red light.
Development of the laser, initially demonstrated in a ruby crystal producing a red output at 694.3 nm, has created numerous applications using visible range optics. Visible laser sources include argon ion, copper vapor, helium-neon, ruby, alexandrite, semiconductor diode lasers and the second harmonics of Nd: YAG and Nd: YLF. Broadband visible sources include tungsten-halogen incandescent lamps and xenon arc lamps. Narrowband incoherent sources such as mercury vapor lamps, sodium lamps, and other spectral lamps are also in common use.
There are many glass types, which can be used to manufacture visible optics. These glasses are defined according to their refractive index and dispersion. They may be selected by an optical designer, for use in complex systems, which minimize the effects of optical aberrations. An optical glass, which has become dominant for use throughout the visible spectrum, is Schott BK7. The properties of this glass make it ideal for use in mirrors, windows, prisms and simple lenses. Also, frequently used in synthetic fused silica, which has a good combination of optical, thermal and hardness characteristics. Certain types of crystal are used in the manufacture of optics. Calcite and quartz have a strong degree of bi-refringence making them useful in the manufacture of optics to control the state of polarization. Since the transmission of most visible range optical materials extends partly into the UV and through the near infra-red, many of these optics may also be used in other parts of the spectrum.
Coatings, which are designed to suit the index of the substrate material, can be applied to modify the transmittance, reflectance, wavelength selectivity and polarization of light incident on the coating. This provides a vast array of optical components, which may be used to modify the nature of light in a controlled manner.
Lambda has considerable experience in the design, manufacture, and coating of visible range optics.
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