ABSTRACT
We report on a displacement metrology setup that provides sub-pm resolution in air. The setup is based on a Fabry-Perot cavity. However, unlike current Fabry-Perot cavity based displacement setups we incorporate a novel fs-laser based arbitrary wavelength synthesizer that provides efficient suppression of atmospheric disturbances while providing very wide and precise tuning of the output wavelength. The wavelength synthesizer provides sub-10 attometer wavelength resolution. The setup provides subpm length stability for integration times of up to one minute and sub-10 pm for up to half an hour without airtight enclosure of the Fabry-Perot cavities.
ABSTRACT
We present an arbitrary optical single-frequency generator based on a femtosecond optical frequency comb. The functions of this device are comparable to those of a radio-frequency synthesizer. However, this device operates at hundreds of terahertz. The absolute frequency accuracy of this synthesizer is approximately 1 kHz at a 282 THz carrier frequency. The stability is approximately 2 x 10(-14) at 100 s, and the tuning speed exceeds 30 GHz/s. This source demonstrates the integration of a phase-locked optical comb into a versatile and easy-to-use system for the generation of tunable, absolute optical frequencies. By using downconversion, one could generate tunable terahertz frequencies that are phase locked to a microwave reference, such as a Cs atomic clock, and high-precision interferometry could benefit greatly from the stability and accuracy of this widely tunable source.
ABSTRACT
A new spatial light modulator that uses electroabsorption induced by the Franz-Keldysh effect in a GaAs single crystal is proposed. The device has the same structure as the Pockels readout optical modulator, is driven by a high ac voltage, and is operated in the superprime mode. Its high-frame-rate (over 500-Hz) operation, high contrast ratio (350:1), and large gamma characteristics (2.47) were experimentally confirmed in the transmission mode, although its operating-wavelength (readout) region is restricted to a narrow band near the band gap. In the reflection mode, however, this device has a high contrast ratio and large gamma characteristic (approximately 5), offering the possibility of its use as a nonlinear device.
ABSTRACT
A new spatial light modulator that uses the electroabsorption and the electro-optic effects in a GaAs single crystal is proposed. The device has the same structure as a Pockels readout optical modulator and can be operated at a frame rate higher than 500 Hz. When the electroabsorption and the electro-optic effects are combined, the dynamic range (contrast ratio) becomes larger than that which results when either effect is used singly. It was experimentally confirmed that the modulator has a high contrast ratio (greater than 2000:1), high sensitivity, and consequently large gamma characteristics.
ABSTRACT
The contrast ratio of an optically addressed spatial light modulator that uses electroabsorption in a GaAs single crystal is discussed experimentally and theoretically. The modulator has the same structure as a Pockels readout optical modulator. The contrast ratio depends strongly on the change in the absorption coefficient and on the thickness of the GaAs crystal. From the experimental results and from theoretical investigations of the Franz-Keldysh effect, the change in the absorption coefficient is estimated by use of the quadratic equation of an applied electric field that is not excessively strong. Under this condition, an optimum thickness of the GaAs crystal plate that will yield the maximum contrast ratio can be determined.
