Laser and Photonics
bulletLaser Diode and DPSS Laser system
bulletHigh Power Tunable External Cavity Diode Lasers
bulletNd:YAG Laser Systems
bulletSpectral Products & CVI Laser
bulletExcimer Lasers
bulletSynrad Lasers
Calibration and Measuring Instruments
bulletGauge Calibration Instruments
Flatness and Roughness Interferometer
bulletCorning Tropel Interferometer system
bulletMask Aligner & Spin Coater equipment
Imaging and Spectroscopy system
bulletPCO Imaging High Performance Camera system
bulletCustomer Laser Spectroscopy and High Resolution Imaging System
Industrial and Manufacturing

Filters and Filter Wheels article


  When used in conjunction with appropriate detectors, filters form basic wavelength selective detection systems. A filter spectrometer has the advantages of simplicity, high signal to noise ratio, low cost and high throughput. A rotatable filter wheel allows multiple filters to be mounted and sequentially selected into the light path.

A filter-based spectrophotometer


  The combination of filters in the light path, that have characteristic transmission curves, generates variable pass bands. When equipped with stepping motors and computer interfaces, the filter wheels can be automated to perform programmed sequences. Applications of filter wheels have been found in atomic spectrometry, environmental monitoring, illuminators, laser spectroscopy, and so on.


  • Center Wavelength:
       The arithmetic mean of the pass band expressed in nanometers.
  • Percent Transmission:
       The amount of power received by the detector compared to the total power available. The traditional formula is %T = I/I0 x (100), where I0, is the incident power and I is the transmitted power.
  • Half Bandwidth:
       The width of the pass band in nanometers at the half-power points of the pass band. It is often expressed as full width at half maximum (FWHM).
  • Out-of-Band Rejection (Blocking):
       The amount of energy, outside the filter pass band, reaching the detector. It is often expressed as an absolute level, such as 10-4, meaning there are no transmission peaks outside the pass band exceeding 0.0001 T or 0.01%T. The rejection range in nanometers must accompany this specification.
  • Band Pass Shape:
       Pass band shapes can vary from triangular to nearly square. The number of cavities involved determines the overall shape.

Diagram for filter characteristics


Spectral Products & CVI Laser