The energy levels of an optically active quantum system can be shifted via the AC Stark effect by applying a strong, far-detuned laser. In addition to achieving a spin-selective AC Stark shift larger than 20 GHz, we observe a small Overhauser shift of approximately 1 GHz in a single negatively charged InGaAs quantum dot. We attribute this small shift to dynamic nuclear polarization via electron spin pumping induced by the high power, although far-detuned AC Stark laser. Low power scans reveal two regimes: high power where the frequency shift is linear in AC Stark laser power, and low power where the behavior is non-linear. Linewidth analysis provides a method to quantify the effect of the AC Stark laser on the nuclear spin environment, which in turn affects the quantum dot transitions.
We have developed two single-chip CCD sensor architectures for high-speed, 3-channel color imaging. Both are line-scan sensors for Time Delay and Integration (TDI) imaging. One architecture achieves a sub-microsecond TDI register shift time by contacting metal to poly-Si gates through the imaging regions. The other has no metal in the imaging regions and requires a longer shift time. Both sensors are capable of 40 MHz data rate per channel. Line rates for 2048-pixel devices of 16.5 and 18.5 kHz (shift times of 7.5 and 0.7 microsecond(s) /stage) are achieved.
We have developed a linescan sensor suited for high image quality, high-resolution, high-speed imaging. The 6k-pixel sensor has: four corner outputs each operating at 40 MHz for high scanning speed; 7 micrometers pixels for shorter sensor length and simpler optical design; an exposure control and antiblooming structure that does not produce imaging artifacts; 9.5 (mu) V/e charge conversion efficiency at the output for enhanced sensitivity and dynamic range under light-starved conditions; optimized pinned photodiodes for low image lag (< 350 electrons) and enhanced UV response (> 40% QE at 250 nm); 100% fill factor down to the deep UV; a pixel storage structure that suppresses photosite-to- shift-register optical crosstalk; highly linear output structures and amplifiers (< 1% non-linearity); matched 5- V 2-phase clocks that can be driven with off-the-shelf CMOS drivers; output waveform shape that allows 40-MHz CDS; and photoresponse non-uniformity that is < +/- 2% of the signal.
Today's imaging systems utilize fast operation to increase their throughput. At high line rates the illumination required to collect a reasonable image becomes prohibitive. Time delay and integration (TDI) offers greatly enhanced responsivity to allow faster operation in terms of line rates. This combination of sensitivity and speed is unmatched in other sensor architectures. The standard multi- stage source follower output amplifier usually involves a trade off between speed and sensitivity through sizing of the first FET. We present a high bandwidth and sensitivity, scalable architecture for readout of TDI sensors. A key component of this architecture is the minimization of output amplifier load and parasitic capacitance. The methodologies used in the design and modeling of the output structure will be presented. This basic model has been confirmed over a range of device dimensions. A 4096 element, multi-tap TDI image sensor incorporating this architecture has been fabricated using a standard CCD process. Discrete and in- camera measurements will be presented demonstrating operation at > 100 kHz line rates and with > 300 V/((mu) J/cm2) peak responsivity. Methods of controlling and reducing the stray loading on the sensor output will also be discussed.
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