Generation of Low-Cost User-Customizable Neutral Density Filters and the Involvement of Undergraduate Researchers

In research and teaching laboratories, optical attenuation
of a
light source is often required on short notice, yet access to suitable
filters may be limited, resulting in delays or increased expense.
For monochromatic applications, attenuation can be achieved using
individual solutions of absorptive dyes. However, broadband or spectral
work typically necessitates a suite of neutral density (ND) filters
covering the desired wavelength range and attenuation levels. This
work presents a low-cost, customizable approach for formulating liquid
ND filters from common laboratory dyes. Two scenarios are considered:
laboratories sourcing dyes for purchase and those leveraging existing
dye inventories. An example ND solution prepared from in-house materials
rivals commercial ND filters: from 425 to 575 nm, abs. range 2.04–2.16
(0.7–0.9%T), absavg = 2.09 (0.8%T), and s.d.abs = 0.03. This stock solution can be diluted as needed and
is compatible with a range of optical systems (e.g., OPO lasers, fluorescence
setups). The formulation strategy is generalizable to other dye sets
and application requirements.