The following example shows Greek letters and mathematical symbols in the x and y axis titles.

; Define the data.
t = 0.1*FINDGEN(200)
y = SMOOTH(RANDOMU(seed,200), 5)

; Draw the plot
p = PLOT(t,y,'b', $  XTITLE='Gap Distance ($\AA$)',$
   YTITLE='Volts ($\mu$V)', $  FONT_SIZE = 20,$
   DIMENSION=[640,512], $  SYMBOL = 'circle',$
   SYM_FILLED = 1, \$
   SYM_FILL_COLOR = 'gold')


For complete information on using the syntax, see TEXT.