This is the HO-WCB-40-3, a 40 mm diameter Circular Flat Window made from N-BK7 glass, a popular material in the optical industry due to its excellent optical properties. The window has a thickness of 8mm, making it suitable for applications that require a substantial optical path length while maintaining a compact form factor.
The window is uncoated, meaning it does not have any anti-reflective or other surface coatings. This can be beneficial in applications where the natural properties of the glass are desired, or where cost considerations are a factor. However, it's important to note that uncoated windows can have higher reflectivity, which may need to be considered in the overall system design.
This item is offered by Holmarc Opto-Mechatronics, a reputable vendor known for their high-quality optical components. The product page on their website (https://www.holmarc.com/windows_circular.php) indicates that it is in stock, providing assurance of quick delivery.