Second order nonlinear mediums, like lithium niobate and KTP, have been extensively studied for various applications, such as single photon detection and terahertz generation. In this dissertation, several novel applications in second order nonlinear crystals have been studied in depth, as follows:
1) Highly efficient single-photon level detection at 1.57&mgr;m. There exists an absorption peak for carbon dioxide at 1.57 &mgr;m, which is extremely desirable for NASA ASCENDS program, due to the fact that it can monitor CO2 concentration in the outer space. Commercially available detectors at IR wavelengths suffer from high dark counts up to 105 /s, as well as low quantum detection efficiencies, usually with values between 10% and 15%. In contrast, single-photon counting in near-IR (600–800nm) can be performed efficiently with silicon APDs. Single photon counting modules with dark counts lower than 25/s and detection efficiency in the range 50% to 70% are commercially available. We took advantage of silicon APDs, implemented efficient conversion from 1.57&mgr;m to visible with more than 60% of internal quantum conversion efficiency and demonstrated almost noise-free measurement. As a result, our detection system has reached an ultralow noise level of 25 s-1 and a detectable photon rate of 81 s-1 for communication band.
2) Non-destructive method for evaluating domain errors in PPLN waveguide using surface-emitting geometry (SHG). Periodically-poled lithium niobate (PPLN) waveguide is an efficient nonlinear structure for generation of tunable coherent radiation based on optical parametric oscillators and single-photon detection based on frequency up-conversion. In order to achieve efficient conversion, quasi-phase-matching (QPM) must be satisfied. However, imperfections of periodic domains due to fabrication errors such as linear taper of domain period, duty cycle error, and randomness of domain period significantly affect the performance of the PPLN waveguide. We developed a fast and non-destructive method to statistically evaluate the domain quality of PPLN. The resolution can reach 0.5nm.
3) Anti-Stokes enhancement observation in lithium niobate waveguide. Anti-Stokes signals are much weaker than Stokes counterparts due to significantly reduced phonon occupation numbers. We now measure the forward- and backward- propagating anti-stokes photons from waveguide and observed enhancement factor at least one order of magnitude higher than in the bulk. The required pump power was reduced five orders of magnitude to only a few microwatts. Under two propagation configuration, we observed different layouts of anti-stokes peaks for lithium niobate.
4) Terahertz generation through difference frequency generation of two close wavelength IR beam in Gallium Phosphide (GaP) stacks. By stacking alternatively rotated GaP plates, we reached maximum terahertz photon conversion efficiency of 40%. The corresponding peak power generated inside the four GaP plates approaches 4kW. As the number of plates is increased from four to five, the THz output power is significantly decreased, due to back parametric conversion.
|Advisor:||Ding, Yujie J.|
|Commitee:||Bartoli, Filbert J., Kumar, Sushil, Tansu, Nelson, Vavylonis, Dimitrios|
|School Location:||United States -- Pennsylvania|
|Source:||DAI-B 76/11(E), Dissertation Abstracts International|
|Keywords:||Nonlinear optics, Raman scattering, Single photon detection, Sum frequency generation, Terahertz generation|
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