What are the applications for square rounded corner windows?
Vacuum cavity observation windows, high ressure sensor protection windows, laser sealing windows, underwater optical equipment.

What is the refractive index of BK7 (K9)?

折射率  Refractive Index
	λ〔 nm〕
n2325.42	2325.42		1.489640
n1970.09	1970.09		1.495235
n1529.58	1529.58		1.501060
n1060.0	1060.0		1.506743
nt	1013.98		1.507356
ns	852.11		1.509828
nr	706.52		1.512901
nC	656.27		1.514326
nC '	643.85		1.514723
nHe-Ne	632.8		1.515092
nD	589.29		1.516728
nd	587.56		1.516800
ne	546.07		1.518721
nF	486.13		1.522376
nF '	479.99		1.522830
ng	435.83		1.526690
nh	404.66		1.530251
ni	365.01		1.536288
n313.18	313.18		1.548455
n302.15	302.15		1.552035

What are the advantages of square rounded corner windows?
1. Rounded corners eliminate stress concentrations at right angles, reducing the risk of window rupture during installation or under pressure (especially suitable for high pressure or vacuum environments).
2. The rounded corners allow for easy fitment of the O-ring to improve sealing performance (compared to right angled square windows that are prone to leakage due to minor misalignments).
3. Rounded corners prevent sharp edges from scratching sealing materials or mounting fixtures, extending service life.
4. Rounded corners reduce the diffraction effect of light beams at the edges, which is especially beneficial for high precision optical systems (e.g. interferometers, laser collimation).