Tunable diode laser frequency stabilization and its applications in temperature measurement

Sammanfattning: The frequency of two external cavity diode lasers tuned to the two transitions at 410 nm and 451 nm of indium are stabilized in this thesis. A hollow cathode lamp of indium atoms is used as a low pressure source of indium atoms in the locking process. Two frequency stabilization methods, wavelength modulation spectroscopy (WMS) and polarization spectroscopy (PS), are used in the thesis for the laser locking. In both methods a computer generated sweeping current is sent to a diode laser to produce a wavelength scan around a resonant transition of indium. The laser passes through the lamp and recorded on a photodiode. The recorded signal will be transferred to a computer program. The program, in the case of wavelength modulation spectroscopy locking technique, reduces the scanning range in order to lock the laser to the transitions of indium atoms. The polarization spectroscopy locking program sets the diode laser frequency to the specified transition of indium atoms to lock the laser. The frequency stabilized lasers are used to conduct temperature measurements in an indium seeded flame with two-line atomic fluorescence. A flow of nitrogen gas seeds trimethylindium molecules to the flame and the exothermic combustion processes in the flame breaks the trimethylindium molecule bonds to produce free indium atoms. Two line atomic fluorescence thermometry technique is used to measure the temperature of the flame. A thin sheet of a stabilized diode laser is used to excite indium atoms. Frequency stabilization of the two lasers was done within 250 MHz for WMS and 110 MHz for PS allowing for high precision temperature measurements. The preliminary temperature measurements showed great potential for future measurements in combustion environments.