Tunable la­sers

Our wor­king group has been dea­ling with the de­ve­lop­ment, mo­di­fi­ca­ti­on and cha­rac­te­riza­t­i­on of tunable laser sour­ces for se­ver­al years. Most of these con­sist of a laser diode as ac­tive me­di­um and an ex­ter­nal re­so­na­tor. Lat­ter one re­sults from a se­pa­ra­te ex­ter­nal mir­ror and the non-coated backsi­de of the laser diode, whe­re­as the front side of the laser diode is an­ti-re­flec­tion-coated. The most used geo­me­try in our group is the FTE­CAL geo­me­try (Fou­rier-Trans­form Ex­ter­nal Ca­vi­ty Laser), where the dif­fe­rent wa­ve­lengths of the emit­ted light are spa­ti­al­ly se­pa­ra­ted and reach the ex­ter­nal mir­ror at dif­fe­rent points. The spa­ti­al se­pa­ra­ti­on is ac­com­plis­hed by put­ting a dif­frac­tion gra­ting in the op­ti­cal path. With a lens, the first or mi­nus-first order of the dif­frac­ted light is di­rec­ted to the ex­ter­nal end mir­ror in that way, that the laser light is im­pin­ging as a ho­ri­zon­tal­ly se­pa­ra­ted spec­tral con­ti­nu­um, and re­flec­ted di­rect­ly in its­elf. By use of a nar­row slit-aper­tu­re it is now pos­si­ble to select the wa­ve­length for which re­flec­tion is gua­ran­teed. Thus, only for this wa­ve­length the re­so­na­tor exists.

Fig. 1: Sketch of the FTE­CAL-geo­me­try with pulse compressor

The sket­ched FTE­CAL-geo­me­try is used for dif­fe­rent ap­p­li­ca­ti­ons: For ex­amp­le for the ge­ne­ra­ti­on of tera­hertz-ra­dia­ti­on. In this case, la­sing is en­su­red for two dif­fe­rent wa­ve­lengths by using two slit-aper­tu­res. In a non­line­ar me­di­um, these two wa­ve­lengths can ge­ne­ra­te the dif­fe­rence-fre­quen­cy, which is in the tera­hertz-ran­ge. Ano­ther field of ap­p­li­ca­ti­on is me­di­cal ima­ging: tunable laser sour­ces are of in­te­rest for ap­p­li­ca­ti­ons like OCT (Op­ti­cal Co­he­rence To­mo­gra­phy) and TGHI (Time Gated Ho­lo­gra­phic Ima­ging), for in­stan­ce.


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)rub.de
RUB campus map & travel instructions

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)rub.de

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