Hipke, Arthur (2016): Dualfrequencycomb twophoton spectroscopy. Dissertation, LMU München: Fakultät für Physik 

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Abstract
This thesis reports on experimental demonstrations of a novel direct frequencycomb spectroscopic technique for the measurement of one and twophoton excitation spectra. An opticalfrequencycomb generator emits a multitude of highly coherent laser modes whose oscillation frequencies are evenly spaced and uniquely determined by only two measurable and adjustable radiofrequency parameters and the integervalued mode number. Direct frequencycomb spectroscopy can traditionally be performed by scanning the comb lines of the frequency comb across the transitions of interest and measuring a signal that is proportional to the excitation by all comb lines in concert. Since the modes that contribute to the excitation cannot be singled out, transition frequencies can only be measured modulo the combline spacing with this scheme. The so arising limitations are overcome by the technique presented here, where the first frequency comb is spatially overlapped with a second frequency comb. Both combs of this socalled dualcomb setup are ideally identical except for having different carrierenvelope frequencies and slightly different repetition rates. The interference between the two combs leads to beat notes between adjacent comb lines, forming pairs (with one line from each comb) with an effectively modulated excitation amplitudes. Consequently the probability of excitation by any given combline pair is also modulated at the respective beatnote frequency. These beatnote frequencies are spaced by the repetitionrate difference and uniquely encode for individual combline pairs, thus enabling the identification of the comb lines causing an observed excitation. In a first demonstration, Dopplerlimited onephoton excitation spectra of the transitions 5S_{1/2}5P_{3/2} (at 384 Thz/780 nm), 5P_{3/2}5D_{3/2}, and 5P_{3/2}5D_{5/2} (both at 386 Thz/776 nm), and twophoton spectra of the 5S_{1/2}5D_{5/2} (at 2x385 Thz/2x778 nm) transition, agreeing well with simulated spectra, are simultaneously measured for both stable Rb isotopes. Within an 18s measurement time, a spectral range of more than 10 THz (20 nm) is covered at a signaltonoise ratio (SNR) of up to 550. To my knowledge, this is the first demonstration of both dualcombbased twophoton spectroscopy and fluorescencebased dualcomb spectroscopy. In a followup experiment probing the same sample and twophoton transitions, the Dopplerresolution limit is overcome by implementation of an antiresonant ring configuration. Cancellation of the firstorder Doppler effect makes it possible to resolve 33 hyperfine twophoton transitions. The highly resolved (1 MHz point spacing), narrow transitionlinewidth (5 MHz), accurate (systematic uncertainty of ~340 kHz), highSNR (10^4) spectra are shown to be consistent with basic simulationbased predictions. As the spectral span is, in principle, only limited by the bandwidths of the excitation sources, the acquisition of Dopplerfree twophoton spectra spanning 10s of THz appears to be in reach. To my knowledge, this is the first demonstration of Dopplerfree Fouriertransform spectroscopy. Lastly, the possibility of extending the technique's scope to applications in the field of biochemistry, such as twophoton microscopy, are explored. To that end, first highspeed, lowresolution (>>1 GHz) experiments are carried out identifying combstabilization requirements and measurement constraints due to the limited dynamic range of the presented highly multiplexed spectroscopic technique.
Dokumententyp:  Dissertation (Dissertation, LMU München) 

Keywords:  Direct FrequencyComb Spectroscopy, FourierTransform Spectroscopy, DopplerFree Spectroscopy, TwoPhoton Spectroscopy, DualComb Spectroscopy 
Themengebiete:  500 Naturwissenschaften und Mathematik
500 Naturwissenschaften und Mathematik > 530 Physik 
Fakultäten:  Fakultät für Physik 
Sprache der Dissertation:  Englisch 
Datum der mündlichen Prüfung:  8. April 2016 
1. Berichterstatter/in:  Hänsch, Theodor W. 
URN des Dokumentes:  urn:nbn:de:bvb:19193602 
MD5 Prüfsumme der PDFDatei:  d26c294f42b310efe55d0da4b0160c22 
Signatur der gedruckten Ausgabe:  0001/UMC 23727 
ID Code:  19360 
Eingestellt am:  21. Apr. 2016 12:57 
Letzte Änderungen:  21. Apr. 2016 12:57 