Spectrogon designs and manufactures optical interference filters employing state of the art deposition technology and the most advanced design criteria available.

Custom sizing

All filters in this catalogue are manufactured to a standard size of 25.4 mm diameter. Most of these filters are suitable for dicing and/ or turning down (of the diameter). If smaller sizes are required, SPECTROGON´s custom sizing service is available at a modest surcharge. Please contact our sales engineers for further assistance.

Spectral Scans

All filters are shipped with an individual spectral scan or, in the case of multiple similar filters in the shipment, one scan per lot. The spectral scans are taken at room temperature and at normal angle of incidence showing the relevant wavelength region of the filter. Special spectral scans (other than at normal angle of incidence, extended curves of blocking and bandpass regions, and other than room temperature) can be supplied for an additional cost.

Effects of varying angles of incident beams

The filter wavelengths in this catalogue are listed at normal angle of incidence. If filters are intended to be used at other than normal angle of incidence, the filter´s spectral characteristics have to be considered in order to achieve the intended spectral function. All interference filters will shift to shorter wavelength as the angle of incidence of a collimated beam deviates from the normal. This effect may, to some extent, be used to tune a filter to a desired shorter wavelength. The angle effects can be approximately calculated by the following formula:

	(1.1)

• Definition of Common Terms

Typical values for the effective index for an infrared filter are in the region 1.5-2.8.

At high angles of incidence, 30°or more, transmission will decrease and a distortion of the filter bandpass shape will eventually occur.

Fig. 1 Wavelength shift as a function of angle of incidence (example)

Fig. 2 Wavelength shift as a function of angle of incidence

Effects of varying temperature

Interference filters will shift to longer wavelength with increasing temperature/ shorter wavelength with decreasing temperature. This wavelength shift is caused by thermal expansion/contraction of the coating materials. The shift is often expressed in nm/§C and is normally extremely small (0.01-0.2 nm/°C). The temperature effect can be approximately calculated by the following formula:

	(1.2)

Fig. 3 Wavelength shift as a function of temperature

Definition of Common Terms

Cleaning and handling of filters

SPECTROGON's filters are designed and manufactured to withstand the most stringent environmental conditions. However, all optical components deserve special consideration in handling, caring and storage. All SPECTROGON filters are inspected prior to shipment and packaged in special protective containers. No extra cleaning should be necessary upon receipt.

All unnecessary handling of filters should be avoided to reduce the possibility of damage. The filters should be handled by the edges. Try to avoid handling the filter surfaces. Preferably, all work with the filters should be done in a clean environment, eg. laminar flow cabinet or similar. Ideally, normal clean room procedures should be applied.

If a filter surface is dirty or stained, it can possibly be cleaned. In most normal cases filters may be cleaned with a solution of lukewarm water and mild detergent, providing the substrate and/or the coating is not water soluble, according to the following procedure:

1. Wet a lens cleaning tissue with water/mild detergent solution and wipe the filter surface gently until the surface is clean.
2. Rinse off with distilled water and immediately wipe dry with a lens cleaning tissue.

If the filter is left to dry in air permanent drying stains may appear.

Impurities that are not cleaned with the water/mild detergent method or if the substrate/coating is soluble in water, isopropyl alcohol or acetone cleaning can be used.

1. Wet a lens cleaning tissue with the solvent and trail wipe the surface several times until the surface is clean.
2. Thereafter, immediately wipe dry with a dry lens cleaning tissue.

If in doubt, contact one of our SPECTROGON sales engineers by e-mail on sales.se@spectrogon.com