E = e − − i ω ω t ∑ ∑ l , m l ( l + 1 ) [ a E ( l , m ) E l , m ( E ) + a M ( l , m ) E l , m ( M ) ] B = e − − i ω ω t ∑ ∑ l , m l ( l + 1 ) [ a E ( l , m ) B l , m ( E ) + a M ( l , m ) B l , m ( M ) ] ,