Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Schematic diagram of excited-state absorption (w’ > w1, w0). E0, E1, and E2 represent ground state, intermediate, and excited state, respectively. When one ion or electron in the E0 state absorbs one photon, it is first excited to the E1 state; after sequentially absorbing the second photon, it can jump to the excited state E2 and emit higher energy photons when coming back to the ground state.
