Optical Pulse Shaping For Chirped Pulse Interferometry And Bio-Imaging

Bio-imaging;Non-linear optics;Chirped Pulse Interferomtry;Onion;Physics

Schreiter, Kurt

University of Waterloo

关键词: Bio-imaging;    Non-linear optics;    Chirped Pulse Interferomtry;    Onion;    Physics;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/6238/1/Schreiter_Kurt.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Biomedical imaging requires high resolution to see the fine features of a sample andfast acquisition to observe live cells that move. Optical coherence tomography (OCT) isa powerful technique which uses optical interference for non-invasive high resolution 3Dimaging in biological samples.The resolution of OCT is determined by the length over which the light used will in-terfere. Unfortunately, dispersion hurts the imaging resolution by broadening interferencefeatures. A technique called quantum-OCT (QOCT)[1] is immune to dispersion but re-quires entangled photon pairs. The need for entanglement drastically reduces the numberof photons available for imaging, making QOCT too slow to be practical. Chirped-pulseinterferometry (CPI) is also immune to dispersion. A chirped pulse is one where the fre-quency, or colour, of the light changes from red to blue from one end of the pulse to theother. CPI relies on frequency correlations created by applying different chirps to two sep-arate pulses. This method had the disadvantage of being limited to a single predeterminedchirp rate, and discarded 50% of the power. However CPI has better resolution than OCT,automatic dispersion cancellation, and 10,000,000 times the signal strength of QOCT [13].A new, much more flexible and efficient method of CPI will be demonstrated by creatingthe frequency correlations entirely in a single pulse. This new method is referred to as non-linear chirped pulse interferometry (NL-CPI).The non-linear chirp required in NCPI is very difficult to produce using only conven-tional optics. In this thesis we document the construction and characterization of a newmethod of creating the desired chirp using a programmable pulse-shaper (PS). We build aPPS and then demonstrated its functionality by compressing a 105nm FWHM bandwidthpulse to under 17f s, near its transform limited time duration. We also show that thevalues given to the PPS for dispersion are accurate by calculating and then compensatingthe dispersion caused by various optical elements in the CPI interferometer.Conventional OCT systems are immune to dispersion common to both arms of theinterferometer. Non-linear interferometers experience broadening due to this dispersion,making them more difficult to use with fibre based interferometers common in conventionalOCT. We show that NL-CPI can compensate for dispersion common to both arms of theinterferometer, making NL-CPI more appealing as a replacement for conventional OCT.In this thesis we experimentally implement and demonstrate a prototype setup usingnon-linear CPI for dispersion-cancelled imaging of a mirror, with a resolution comparableto conventional OCT systems. We then use the system to produce 2-D cross sectionalimages of a biological sample, an onion. Q-OCT has previously been used to image anonion[16], but required treating the onion with gold nano particles to achieve a usefulsignal. The onion we used had no special treatment. In addition our axial scanning rateis also 10000 times faster than Q-OCT.