The NE2R04B is a Neutral Density Filter from Thorlabs, designed with a circular base shape and a diameter of 50.8 mm. This filter is made of n-bk7 schott material and has a thickness of 0.7 mm, making it a thin lens type. The filter features a front and back coating of tho ne04a, providing an optical density of 0.4 at a wavelength of 633 nm.
The catalog number for this item is NE2R04B, and it can be found on the Thorlabs website, where it is currently in stock. The link to the product page is provided for your convenience. This filter is sourced from Thorlabs, a reputable vendor known for its high-quality optical elements.