Neutral density filters solve the most ordinary problem in an optical laboratory or instrument: too much light. Detectors saturate, cameras overexpose, and laser measurements peg their ranges. An ND filter attenuates the whole working band by a specified factor — expressed as optical density — while ideally changing nothing else, so the system behaves exactly as before, only dimmer. In laser and instrument service, which is the context of this page, ND filters set exposure and measurement ranges and protect sensors during alignment.
The manufacturer's documented range includes a combined laser infrared optical colour glass bandpass / ND filter listing, and the filter group lists neutral density filters as a family in their own right. Absorptive glass ND and reflective coated ND behave differently under power — absorptive glass takes the energy into the glass, coated ND reflects it away — and the quotation conversation covers which construction suits your power level and band.
Specifying an ND Filter
- Optical density — the attenuation factor required; densities add when filters are stacked.
- Working band — neutrality is always specified over a band, never over all wavelengths at once.
- Construction — absorptive colour glass or reflective coating, matched to the power the filter must handle.
- Size and mounting — free aperture, or a mounted format for a filter wheel or holder.
ND filters pair with the rest of the instrument filter set — an attenuation step can sit in front of a bandpass-selected channel. This page addresses optical attenuation for lasers and instruments; photographic ND filters for cameras are a consumer variant of the same physics with different housings. Minimums and pricing are confirmed per specification in the written quotation.
Frequently Asked Questions
What does optical density mean?
It is the logarithmic measure of attenuation: each density unit reduces transmission by a factor of ten. Stacked filters add their densities.
Absorptive or reflective ND for a laser?
Reflective (coated) ND is generally preferred at higher powers because it reflects the rejected energy instead of absorbing it as heat. State the power in the enquiry.
Can ND filters be combined with bandpass filters?
Yes — attenuation and wavelength selection are independent jobs, and the two filter types can be combined in one instrument path.
Stacking, Calibration and Set Behaviour
ND filters are used in sets as well as singly, and set behaviour deserves a note. Densities add when filters stack, so a small set of density values covers a wide attenuation range in steps. Two cautions apply. First, stacked absorptive filters multiply their imperfections as well as their densities. Second, in laser service the first filter in the stack takes the full incident power, so the set should be arranged with the most robust construction facing the beam and the power stated in the enquiry so the construction can be chosen accordingly. For instruments, the cleaner pattern is to fix the attenuation into the design — one specified density, calibrated into the measurement chain — rather than leaving operators to improvise stacks. State whether the filter serves a bench, a prototype or a shipped instrument, and the quotation will aim at the right pattern.
Request a Quotation
Tell us the component, material, dimensions and coating you need. Pricing and lead time for your specification are confirmed in the written quotation.