We are using mul­ti­ple tech­ni­ques to in­ves­ti­ga­te the op­ti­cal gain, as the com­mon me­thod of Hakki and Paoli, a self de­ve­lo­ped trans­mis­si­on me­thod or the all op­ti­cal stri­pe length me­thod. This enables us to in­ves­ti­ga­te dif­fe­rent type of sam­ples from fully de­ve­lo­ped and pro­ces­sed laser de­vices to un­pro­ces­sed pho­to­lu­mi­nescence sam­ples from early sta­tes of ma­te­ri­al de­ve­lop­ment. We are able to ob­tain tem­pe­ra­tu­re und po­la­riza­t­i­on de­pen­dent gain spec­tra in pul­sed and con­ti­n­uous wave ope­ra­ti­on in order to get de­tai­led in­for­ma­ti­on about the re­le­vant gain me­cha­nism and the un­der­ly­ing tran­si­ti­on and en­er­gy sta­tes.

Mo­re­over ex­pe­ri­men­tal gain re­sults me­a­su­red in our group, can be com­pa­red with cal­cu­la­ti­on based on a microsco­pic ma­ny-bo­dy theo­ry, ob­tained by the groups of S.W. Koch, Uni­ver­si­ty of Mar­burg and J. Mo­lo­ney, Uni­ver­si­ty of Ari­zo­na, Tuc­son, USA. Such com­pa­ri­sons lead to fur­ther in­sights into the gain me­cha­nism and allow di­rect de­ve­lop­ment and op­ti­mi­sa­ti­on of the laser ma­te­ri­al. Our work is pri­ma­ry fo­cu­sed on the op­ti­cal gain and the gain me­cha­nism of new ma­te­ri­al sys­tems as the me­tas­ta­ble GaIn­NAs sys­tem or quan­tum dot sys­tems.