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Optics Letters

Squeezed-light generation with a mode-locked Q-switched laser and detection by using a matched local oscillator

Orhan Aytür, Prem Kumar

Published Apr 1, 1992• 43 citations
Publisher

Abstract

We report pulsed squeezed-light generation by means of an optical parametric downconverter that is pumped by the second harmonic of a mode-locked Q-switched laser. Using the fundamental beam of the laser as a local oscillator, we observe 2-dB squeezing for a parametric gain of 2.0. This local oscillator, however, is nonoptimal because of its spatiotemporal mode mismatch with the squeezed mode generated by the downconverter. We describe an experiment in which a matched local oscillator is generated with the use of an optical parametric amplifier that is pumped by the same laser as is the downconverter. In this case, 2-dB squeezing is observed for a parametric gain of 1.5. The present experimental setup is limited by the uncontrollable phase fluctuations that prohibit us from making squeezing measurements at higher parametric gains.

DOI
10.1364/ol.17.000529

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Acta Physica Sinica•Jan 1, 2013•3 citations
We report pulsed squeezed-light generation by means of an optical parametric downconverter that is pumped by the second harmonic of a mode-locked Q-switched laser. Using the fundamental beam of the laser as a local oscillator, we observe 2-dB squeezing for a parametric gain of 2.0. This local oscillator, however, is nonoptimal because of its spatiotemporal mode mismatch with the squeezed mode generated by the downconverter. We describe an experiment in which a matched local oscillator is generated with the use of an optical parametric amplifier that is pumped by the same laser as is the downconverter. In this case, 2-dB squeezing is observed for a parametric gain of 1.5. The present experimental setup is limited by the uncontrollable phase fluctuations that prohibit us from making squeezing measurements at higher parametric gains.
Squeezed light with partial coherence is generated via optical parametric amplification (OPA) in a KTiOPO4 crystal that is pumped by the second harmonic of a Q-switched multimode Nd:YAG laser.1 More than 1 dB of squeezing is observed when a proper mode of the downconverted light is homodyned with the 380-ns multilongitudinal-mode local oscillator (LO) pulse. In such a system, large OPA gain is easily obtained in a single-crystal signal-pass setup. The detection of squeezed light is, however, not straightforward. In the usual implementation of a balanced homodyne detection scheme,2 the vacuum-noise level, as measured on a radio frequency spectrum analyzer, is determined by the average LO power. If the LO is derived from a Q-switched laser, as is the case in our experiment, the associated peak power can easily saturate the detectors and the subsequent electronics. To overcome this limitation, we have implemented a hybrid frequency/time domain measurement scheme in which the vacuum noise level is determined by the peak (instead of the average) LO power. The LO average power requirement is thus relaxed and the detector saturation problem avoided.
We report generating squeezed light via parametric down conversion of a Q-switched and frequency-doubled multi-longitudinal-mode Nd-doped yttrium-aluminum-garnet laser. A local oscillator with appropriate temporal incoherence is needed to homodyne detect the generated squeezed light. As a first approximation, we derive the local-oscillator beam from the same multimode laser whose harmonic is used to pump the parametric down-conversion process. 0.08\ifmmode\pm\else\textpm\fi{}0.2 dB of squeezing is routinely observed.
Pulsed squeezed light and intensity-correlated twin beams are generated by means of a traveling-wave optical parametric amplifier (OPA) consisting of a type-II phase-matched KTiOPO4 crystal that is pumped by a Q-switched and frequency-doubled Nd:YAG laser. Q switching of the laser results in a high peak pump intensity and a large peak parametric gain. Squeezed light is generated by amplifying the vacuum input field to the OPA, and it is detected by a balanced homodyne configuration that uses the fundamental beam of the laser as a local oscillator.1 Twin beams are generated by supplying a small input signal to the OPA. The amplified signal and idler beams are direct-detected individually and yield quantum-noise reduction when the two photocurrents are subtracted.
A local oscillator (LO) which can correctly decode the spatiotemporally distorted quadrature-squeezed light generated by means of single-pass traveling-wave optical parametric amplification is experimentally demonstrated. Such a matched LO is automatically produced in our squeezed-light generation scheme. With the matched LO 5.8 \ifmmode\pm\else\textpm\fi{} 0.2 dB [(74 \ifmmode\pm\else\textpm\fi{} 1)%] of quadrature squeezing is observed which, to the best of the authors' knowledge, is the highest observed in any traveling-wave squeezing experiment to date.
We demonstrate experimentally the short pulse amplitude squeezed light from a singly resonant synchronously pumped optical parametric oscillator (SPOPO). The SPOPO operates in the frequency degenerate case and below threshold, with using a periodically poled potassium titanyl phosphate crystal. The pump laser is the second harmonic of a ultrashort mode-locked femtosecond pulse at 850 nm. The reduction of quantum noise of 2.58 dB is obtained experimentally. The squeezing extent is deduced to be 4.48 dB.