Femtosecond pulse laser second harmonic generation on semiconductor electrodes

✍ Scribed by W. Kautek; N. Sorg; J. Krüger

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 545 KB
• Volume: 39
• Category: Article
• ISSN: 0013-4686
• DOI: 10.1016/0013-4686(94)e0043-y

✦ Synopsis

Laser pulses of _ 300 fs duration (300 x lo-Is s) were apphed for second harmomc generatIon (SHG) at & electrodes, for the first tme The frequency doublmg by reflection at surfaces of centrosymmettrc materials like d 1s generated only at the surface due to the breakmg of the crystal symmetry This method 1s particularly Interesting because even buned sobd state interfaces am be studled SHG as a non-hear optical effect needs high dlumma~on power densities This has restncted tts use mamly to metal electrodes Our recent studies wtth ns laser pulses showed that even semiconductor electrodes can be probed wrth SHG If the duratton of the hght pulses IS shorter than any electron transfer reactlon A further advantage of fs pulses IS the fact that dlummatlon fluenccs well below the damage threshold, but stdl with suflkent power denaty, can be chosen In contrast, the use of ns pulses requned an operauon near the damage threshold SI electrodes m contact unth aqueous electrolytes are normally covered by an oxide layer of LO, wth a translhon layer of non-stotchlometnc suboxide SIO, (1 < x < 2) The extenston of tins layer as well as its growth mechanrsm and structure are still under discussIon Surface SHG pronuses to provide drrect mslght mto 011s buned Interface since the SH signal IS generated exactly there An oxide covered 4(111) surface yields an azunuthal SHG dependence as expected from the (1 ll)C,, symmetry Removal of the oxide causes a drop m SH mtenslty ~th a subsequent nse ascnbable to changes of the static electnc field m the transrtlon layer At an oxide covered S~(lll) electrode the SH signal can be modulated by an externally apphed potentml