Development of a Tunable Frequency Shift Filter Using a Praseodymium Doped Y2SiO5-Crystal

In this thesis, a tunable frequency shift filter (FSF) with a 1 ~ 2 MHz passband created in a praseodymium doped Y2SiO5-crystal using a special hole burning technique is developed and tested. The FSF is able to shift the frequency of its passband and the light passing through the passband by applying an external electric field, where the frequency shift is proportional to the applied field. Since most of the current frequency shift techniques require the light to be sent in at certain angles (a specific special mode) to the shifter, the $2\pi$ acceptance angle for light of this FSF makes it unique and work more efficiently and less restrictively. The FSF can also slow down the group velocity of the light pulse passing through its passband at the order of 10^4 to 10^5. The result of the experimental test of the FSF is quite good. For the FSF with a 1 ~ 2 MHz passband, the light is slowed down to c/10^4 ~ c/10^5. For a 1 MHz FSF, the frequency shift of -4 ~ 4 MHz for both the passband and the light pulse is achieved. The switch-on time for the FSF is around 200 ns limited by the rise time of the electric field.When you look upon the sky enjoying the beautiful aurora in north of Sweden, are you curious what is happening over there? When you go through the security check and have you luggage scanned, do you wonder how the image is shown? It is all about the light-matter interaction! When light meets matter, happens the story. Different stories happen for different matters, and people are using these stories for different purposes. The story (interaction) happening in this project is between light and rare earth ions that doped in a crystal. When light passes through the crystal, it will be absorbed (the story will happen) if the frequency of the light coincides with the transition of the rare earth ion (if the light meets the right matter). A bandpass filter will absorb all light within a certain frequency range except for light having the same frequency as its passband. So light with the frequency different from the passband will be filtered out when passing through the filter. This project is about to create a special spectral filter with praseodymium doped Y2SiO5-crystal using the hole burning technique. How is that? Simply speaking, the light with the frequency equal to the passband is pre-sent into the crystal to interact with the 'right ions'. After the interaction, all the 'right ions' will be burnt away, so when the light having the same frequency as the passband comes, there will be no 'right ions' for it to interact with, thus no absorption will happen. Why do we create such a filter and what is interesting for this filter? Well, with this filter, we could slow down the speed of the light passing in the passband for the order of 10^4 to 10^5! Moreover, by applying an external electric field, the frequency of the passband and the light passing in the passband could be shifted with the frequency shift proportional to the magnitude of the electric field

Development of optical diagnostics of plasma-related phenomena and applications

Optical diagnostics techniques based on coded imaging were developed and applied for plasma-related phenomena and applications. The signal of interest is first encoded with a sinusoid pattern either by structured laser illumination or implement of a diffractive optical element, such as a grating, along the optical path of the signal. The coded signal will then be extracted from the raw data by a lock-in based algorithm, such as frequency recognition algorithm for multipleexposures (FRAME). Two types of non-thermal plasma sources, i.e., gliding arc discharges and nanosecond pulsed discharges, were investigated. Volumetric information of molecular distributions around a gliding arc was captured using laser-induced fluorescence with structured illumination and FRAME. Laser scattering imaging during the formation of a nanosecond pulsed discharge on a at methane-air flame was extracted from luminous plasma emission using structured laser illumination. Furthermore, a technique named periodic shadowing was applied for streak camera measurements, where both higher temporal contrast and effective dynamic range were achieved. The gliding arc plasma discharge was also applied in an industrial prototype burner as plasma-assisted combustion has been proven to be a promising technique to increase energy efficiency as well as reduce environmentally harmful emission. With the help of 0.1% additional energy, the lean blow-out limit of a hundred kilowatt burner was extended from a global equivalence ratio of 0.47 to 0.45

Single-shot 3D imaging of hydroxyl radicals in the vicinity of a gliding arc discharge

Chemical processing by plasma is utilized in many applications. Plasma-related studies, however, are challenging to carry out due to plasmas' transient and unpredictable behavior, excessive luminosity emission, 3D complexity and aggressive chemistry and physiochemical interactions that are easily affected by external probing. Laser-induced fluorescence is a robust technique for non-intrusive investigations of plasma-produced species. The hydroxyl radical (OH) is an interesting molecule to target, as it is easily produced by plasmas in humid air. In this letter, we present 3D distributions of ground state OH radicals in the vicinity of a glow-type gliding arc plasma. Such radical distributions, with minimal plasma emission, are captured instantaneously in one single camera acquisition by combining structured laser illumination and a lock-in based imaging analysis method called FRAME. The orientation of the plasma discharge can be reconstructed from the 3D data matrix, which can then be used to calculate 2D distributions of ground state OH radicals in a plane perpendicular to the orientation of the plasma channel. Our results indicate that OH distributions around a gliding arc are strongly affected by gas dynamics. We believe that the ability to instantaneously capture 3D transient molecular distributions in a plasma discharge, with minimal plasma emission interference, will have a strong impact on the plasma community for in-situ investigations of plasma-induced chemistry and physics

Improved temporal contrast of streak camera measurements with periodic shadowing

Periodic shadowing, a concept used in spectroscopy for stray light reduction, has been implemented to improve the temporal contrast of streak camera imaging. The capabilities of this technique are first proven by imaging elastically scattered picosecond laser pulses and are further applied to fluorescence lifetime imaging, where more accurate descriptions of fluorescence decay curves were observed. This all-optical approach can be adapted to various streak camera imaging systems, resulting in a robust technique to minimize space-charge induced temporal dispersion in streak cameras while maintaining temporal coverage and spatial information

Slow-light-based optical frequency shifter

We demonstrate experimentally and theoretically a controllable way of shifting the frequency of an optical pulse by using a combination of spectral hole burning, slow light effect, and linear Stark effect in a rare-earth-ion-doped crystal. We claim that the solid angle of acceptance of a frequency shift structure can be close to 2π, which means that the frequency shifter could work not only for optical pulses propagating in a specific spatial mode but also for randomly scattered light. As the frequency shift is controlled solely by an external electric field, it works also for weak coherent light fields and can be used, for example, as a frequency shifter for quantum memory devices in quantum communication

Effect of a single nanosecond pulsed discharge on a flat methane–air flame

Successful implementation of plasma-assisted combustion in applied thermal processes heavily relies on how the plasma can be formed as it interacts with the reactive flow and what the effects are of such a plasma on the combustion process. The current study is an experimental investigation of a plasma-assisted lifted flat methane–air flame by a nanosecond pulsed discharge at atmospheric pressure. The nanosecond pulsed discharge, with a pulse duration of 4 ns and an amplitude of 30 kV to 50 kV, is used to stimulate the flame with a repetition rate of 1 Hz. The flame/plasma interactions are investigated with electrical and optical/laser diagnostics to study plasma-formation and its effect on the temperatures and formaldehyde formation. The flame speed seems to be accelerated for tens of milliseconds after the plasma stimulation, without noticeable gas temperature increase at the flame front and in the post-flame region. Formaldehyde is formed in the unburnt region while there is a slight increase in formaldehyde signal in the preheat zone. These results show that a volumetric effect of plasma-assisted combustion can be achieved with a short nanosecond plasma from a single excitation

Experimental Investigation of Plasma Discharge Effect on Swirl Flames at a Scaled Siemens Dry Low Emission Burner

The effect of a Rotating Gliding Arc (RGA) plasma discharge on the flame in a scaled Siemens Dry Low Emission (DLE), SGT-750, burner was experimentally investigated under atmospheric combustion conditions. The central pilot section of the burner, named RPL (rich pilot lean), was redesigned with an integrated high voltage electrode to generate an RGA. The exhaust gas was sampled and analysed in terms of CO and NOx emissions, and the CO emission data show that the RGA extends the lean blow-out limit (LBO). High-speed OH chemiluminescence imaging was employed to understand the transient behaviour of the flame in both conditions with and without RGA and also to study the process of flame re-stabilization by the assistance of the RGA. A flame kernel, initiated around the RGA channel, was observed to play an important role in the re-stabilizing process of the flame. Although the NOx emission for the flame with RGA was found to be higher than that without RGA, it was still less than what previous data show for operating conditions with the RPL flame