Enhanced sensitivity in detection of Kerr rotation by double modulation and time averaging based on Allan variance

Joshua, Arjun and Venkataraman, V (2009) Enhanced sensitivity in detection of Kerr rotation by double modulation and time averaging based on Allan variance. In: Review Of Scientific Instruments, 80 (2).

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Abstract

Experiments in spintronics necessarily involve the detection of spin polarization. The sensitivity of this detection becomes an important factor to consider when extending the low temperature studies on semiconductor spintronic devices to room temperature, where the spin signal is weaker. In pump-probe experiments, which optically inject and detect spins, the sensitivity is often improved by using a photoelastic modulator (PEM) for lock-in detection. However, spurious signals can arise if diode lasers are used as optical sources in such experiments, along with a PEM. In this work, we eliminated the spurious electromagnetic coupling of the PEM onto the probe diode laser, by the double modulation technique. We also developed a test for spurious modulated interference in the pump-probe signal, due to the PEM. Besides, an order of magnitude enhancement in the sensitivity of detection of spin polarization by Kerr rotation, to 3x10(-8) rad was obtained by using the concept of Allan variance to optimally average the time series data over a period of 416 s. With these improvements, we are able to experimentally demonstrate at room temperature, photoinduced steady-state spin polarization in bulk GaAs. Thus, the advances reported here facilitate the use of diode lasers with a PEM for sensitive pump-probe experiments. They also constitute a step toward detection of spin-injection in Si at room temperature.

Item Type:	Journal Article
Publication:	Review Of Scientific Instruments
Publisher:	American Institute of Physics
Additional Information:	Copyright of this article belongs to American Institute of Physics.
Keywords:	gallium arsenide;III-V semiconductors;optical Kerr effect;optical modulation;optical rotation;photoelasticity;remote sensing by laser beam;semiconductor lasers;spin polarised transport.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	01 May 2009 03:25
Last Modified:	19 Sep 2010 05:29
URI:	http://eprints.iisc.ac.in/id/eprint/19556

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