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

## TL;DR

This paper introduces a low-cost method for creating customizable neutral density filters using common dyes, suitable for various optical applications.

## Contribution

The novel contribution is a customizable and affordable method for producing neutral density filters using common dyes.

## Key findings

- An example ND solution from in-house materials matches commercial filters with absorption levels of 2.04–2.16 (0.7–0.9%T).
- The method is generalizable to other dye sets and application requirements.
- The solution is compatible with various optical systems like OPO lasers and fluorescence setups.

## Abstract

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.