Sentence:  It can be readily derived from Eqs. 6.26 and 6.32 that the field generated by these incident evanescent waves inside the slab do SIC not decay away <WSD>exponentially</WSD> from the upper interface, but increases <WSD>exponentially</WSD> as "y" decreases. 
Meaning of the word marked with <WSD> tags:  In an exponential manner.