Optimal frequency band interval to increase optical temporal coherence of thermal light

An optimal bandwidth interval is proposed for increasing the optical temporal coherence of thermal light. The choice of this most intensely emitted frequency interval is based on solving the problem of optimizing the emission spectrum of a black body. The calculated frequency interval is also the narrowest band for the coherence filter for a given value of the total transmitted energy. As a result, the interval found can be used to achieve the highest possible coherent properties at a given level of total energy that has passed. The achieved coherence length values for such optimized bandpass filters are calculated analytically. Some practical applications of the obtained results are discussed.