ENHANCED DETECTION OF UV-INDUCED FREE-CARRIERS BY MULTIPLE PROBE BEAM PASSES INSIDE A CO-DOPED GAGG CRYSTAL

In this work, we have investigated the advantages of increasing the 1064nm CW¹ probe interaction length in a Gd₃Al₂Ga₃O₁₂ (GAGG:Ce,Mg) crystal by multiple internal reflections off two gold-coated parallel faces with entry/exit 0.75mm windows (Fig. 1). Modelling of such geometry enabled a more comprehensive experimental approach in terms of achieved results and time consumption by acquiring incidence angles of interest. Signal enhancement thus is achieved by maximizing free carrier absorption of the probe beam through increasing the path travelled inside the sample. A 266nm pulsed pump of 4.2μJ inducing 1.6 × 10¹⁵ cm^-3 free carriers – two orders of magnitude lower than the previous results – in a cubic GAGG sample (5 × 5 × 5mm³) yielded a 1% signal change using an InGaAs detector. Higher energy pulses of 0.29mJ showed a signal change up to 65%.