Op­ti­cal gain due to in­ver­si­on in an ac­tive me­di­um is the basic re­qui­re­ment for the ope­ra­ti­on of usual se­mi­con­duc­tor la­sers. The­re­fo­re a de­tai­led know­ledge of the gain of a ac­tive se­mi­con­duc­tor me­di­um is in­dis­pensa­ble for de­ve­lo­ping se­mi­con­duc­tor la­sers. Mo­re­over, in­sights into the gain me­cha­nism allow fur­ther im­pro­ve­ments of laser de­vices which can­not be ob­tained by usual in­ves­ti­ga­ti­on of the pho­to­lu­mi­nescence alone. On the one hand a low thres­hold cur­rent re­qui­res a large gain, on the other hand an as broad as pos­si­ble gain spec­tra is im­portant for a large tem­pe­ra­tu­re ope­ra­ti­on range, es­pe­ci­al­ly for ver­ti­cal-ca­vi­ty sur­face-emit­ting la­sers (VC­SELs). Fi­nal­ly a high dif­fe­ren­ti­al gain is cru­ci­al for fast laser dy­na­mics. De­pen­ding on the ap­p­li­ca­ti­on, the gain of the ac­tive ma­te­ri­al has to be op­ti­mi­sed for op­ti­mum per­for­mance.

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.


  • M.R. Hof­mann et al., Emis­si­on dy­na­mics and op­ti­cal gain of 1.3µm (GaIn)(NAs)?GaAs la­sers, IEEE J. Quan­tum Elec­tron. 38, 213 (2002).
  • J Hader et al., Quan­ti­ta­ti­ve pre­dic­tion of se­mi­con­duc­tor laser cha­rac­te­ris­tics based on low in­ten­si­ty photo lu­mi­nescence me­a­su­re­ments, IEEE Pho­ton. Tech­nol. 14, 762 (2002).
  • N.C. Ger­hardt et al., Li­ne­width en­han­ce­ment fac­tor and op­ti­cal gain in (GaIn)(NAs)?GaAs la­sers, Appl. Phys. Lett. 84, 1 (2004).
  • N.C. Ger­hardt et al., Ex­pe­ri­men­tal ana­ly­sis of the op­ti­cal gain and li­ne­width en­han­ce­ment fac­tor of GaIn­NAs/GaAs la­sers, J. Phys.: Con­dens. Mat­ter 16, 1 (2004).


Postal Address

Ruhr-University Bochum
Faculty of Electrical Engineering
and Information Technology
Photonics and Terahertz Technology
Postbox ID 16
Universitätsstraße 150
D-44801 Bochum


Room: ID 04/327
Te­l.: (+49) (0) 234 32 - 23051
Fax: (+49) (0) 234 32 - 14167
E-Mail: ptt+office(at)
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Chair Holder

Prof. Dr.-Ing. Martin Hofmann
Building: ID 04/329
Te­l.: (+49) (0) 234 32 - 22259
Fax: (+49) (0) 234 32 - 14167
E-Mail: martin.hofmann(at)

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