Raman converter for efficient generation of NIR laser radiation
Zusammenfassung der Projektergebnisse
We have investigated 15 crystalline Raman-active materials with respect to their potential of producing new laser wavelengths in the near infrared spectral region suitable for CO2 detection. Among these, we found several candidates which – depending on the pump laser operating around 1 µm wavelength – are appropriate for the development of Raman converters emitting in the spectral range from 1569.9 nm to 1612.9 nm. In case of pumping with a Nd:YAG laser at 1064.15 nm, barium nitrate was determined to be the most feasible option to meet the requirements of the NIR laser source primarily due to its Raman-shift of 1047.4 cm^-1 and its high Raman gain coefficient. Various barium nitrate Raman laser configurations have been studied in detail aiming at high conversion efficiency from the pump to the third Stokes order at 1599 nm which is complicated by strong thermal lensing of the Raman crystal. This phenomenon was extensively analyzed by means of a probe-beam technique and theoretically modeled by numerical simulations. Based on this analysis, a Raman laser pumped by a high power Nd:YAG laser was developed which incorporates compensation of the thermally induced defocusing effect and thus allows for up to 5.5 W output power at the required wavelength. A different Nd:YAG laser was employed to achieve spectral narrowing of the Raman laser radiation. Injection-seeding of the pump as well as of the Raman laser employing narrow bandwidth diode lasers provides frequency-stable output with less than 500 MHz linewidth. Further reduction of the linewidth as well as the frequency fluctuations could be the subject of further investigations and is planned to be realized by an improved injection-seeding concept involving Raman ring resonators. The potential of the Raman converter has been demonstrated by CO2 absorption measurements under laboratory conditions. For this purpose, a detection scheme - developed at the DLR - has been implemented to investigate the absorption characteristics of CO2 in the spectral region around 1599 nm. This was accomplished by tunable diode laser absorption spectroscopy which convincingly verified the line parameters provided by HITRAN database. Finally, the output radiation of the barium nitrate Raman laser was used to detect CO2 in a range of 50 m. CO2 absorption measurements with longer path lengths and the determination of the spectral purity of the Raman converter are planned to be performed in a future project which aims at the investigation of the spectral and spatial coherence properties of SRS devices. Apart from CO2 detection, the multitude of analyzed Raman materials offers the opportunity to adapt the developed Raman converter scheme in order to detect other atmospheric gases like nitrogen monoxide (NO) around 1369 nm or nitrous oxide (N2O) around 1284 nm. In case of 1064 nm pumping, the latter wavelength matches the second Stokes order in the recently investigated Gd0.5Lu0.5VO4 crystal. To conclude, the scientific findings of the present project can be used for the development of high power laser sources emitting at specific wavelengths which are not attainable with conventional laser crystals.
Projektbezogene Publikationen (Auswahl)
- Laser Physics Letters 5 (12), 845-868 (2008)
A. A. Kaminskii, L. Bohatý, P. Becker, J. Liebertz, P. Held, H. J. Eichler, H. Rhee and J. Hanuza
- Applied Physics B 99 (1), 127-134 (2010)
V. A. Lisinetskii, T. Riesbeck, H. Rhee, H. J. Eichler and V. A. Orlovich
- Laser Physics Letters 7 (5), 367-377 (2010)
P. Becker, L. Bohatý, J. Liebertz, H. Kleebe, M. Müller, H. J. Eichler, H. Rhee, J. Hanuza and A. A. Kaminskii
- Laser Physics Letters 7 (7), 528-543 (2010)
A. A. Kaminskii, L. Bohatý, P. Becker, J. Liebertz, H. J. Eichler, H. Rhee and J. Hanuza
- Proceedings of SPIE 7751, 77510Y (2010)
O. Lux, H. Rhee, H. J. Eichler and R. V. Chulkov
- Optics Letters 36 (9), 1644-1646 (2011)
H. Rhee, O. Lux, S. Meister, U. Woggon, A. A. Kaminskii and H. J. Eichler
- Proceedings of SPIE 8182, 818206 (2011)
A. Fix, C. Büdenbender, M. Wirth, M. Quatrevalet, A. Amediek, C. Kiemle and G. Ehret
- Applied Physics B 106, 867-875 (2012)
R. V. Chulkov, V. A. Lisinetskii, O. Lux, H. Rhee, S. Schrader, H. J. Eichler and V. A. Orlovich
- CLEO-QELS-Fundamental Science, JW2A.23 (2012)
O. Lux, H. Rhee and H. J. Eichler
