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Optics Letters

Quantum-noise measurements in high-efficiency single-pass second-harmonic generation with femtosecond pulses

Yongqing Li, Dorel Guzun, Min Xiao

Published Jul 15, 1999• 10 citations
Publisher

Abstract

The quantum-noise properties of single-pass second-harmonic blue-light generation with femtosecond pulses have been measured. A conversion efficiency of as much as 63.5% of second-harmonic generation at 428.8 nm was observed in a KNbO(3) crystal with femtosecond (130-fs) pulses with wavelengths centered at 857.6 nm. The quantum noise on the generated blue light was measured to be 1.0 dB (1.4 dB of squeezing inferred) below the shot-noise limit. The noise reduction was found to be sensitive to the average power and the center wavelength of the input fundamental pulses under the condition of strong pump depletion.

DOI
10.1364/ol.24.000987

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Physical Review Letters•Jun 28, 1999•50 citations
The quantum-noise properties of single-pass second-harmonic blue-light generation with femtosecond pulses have been measured. A conversion efficiency of as much as 63.5% of second-harmonic generation at 428.8 nm was observed in a KNbO(3) crystal with femtosecond (130-fs) pulses with wavelengths centered at 857.6 nm. The quantum noise on the generated blue light was measured to be 1.0 dB (1.4 dB of squeezing inferred) below the shot-noise limit. The noise reduction was found to be sensitive to the average power and the center wavelength of the input fundamental pulses under the condition of strong pump depletion.
Summary form only given. Reports quantum noise measurements in a high-efficiency single-pass sum-frequency generation (SFG) system with a mode-locked femtosecond pulse laser in a noncritical type-I phase-matched KNbO/sub 3/ crystal. The conversion efficiency from fundamental pulses (with a center wavelength at 857.7 nm and a broad spectral linewidth >12 nm) to blue light pulses (with a wavelength at 428.8 nm and a narrow spectral linewidth <9.5 nm) can be greater than 60%. Since the phase-matching width of the KNbO/sub 3/ crystal is only about 0.7 nm, the main mechanism for the blue light generation is the SFG from the pairs of frequency components of the fundamental pulses. The quantum noise on the blue light was observed to be 1.0 dB (1.4 dB inferred) below the shot-noise limit in certain condition. To our knowledge, this is the first quantum noise measurement done in strong pump-depletion region.
We report an experimental demonstration of highly efficient single-pass second-harmonic generation from 859 nm to 429.5 nm with picosecond pulses in a thick KNbO3 crystal. Both the conversion-efficiency and quantum-noise properties of the generated blue pulses are measured at various pump intensities under a strong focusing condition. We find that the variation of the conversion efficiency of the picosecond second-harmonic generation is an oscillatory function of the input pump intensity (with a maximum efficiency of 56.5%) and is sensitive to the position of the input beam focus in the crystal. The quantum noise on the blue beam can be reduced below the shot-noise limit by 20% at low input power.
We present a new heterodyne technique for detecting weak signals beyond the standard shot-noise limited by employing amplitude-squeezed light as the local oscillator (LO) field. The amplitude-squeezed LO field at 428.8 nm is generated from a highly efficient (up to 60% conversion efficiency) single-pass second-harmonic generation in a nonlinear crystal (KNbO3) pumped by femtosecond (130 fs) pulses at 857.7 nm. The weak signal field is introduced from the entrance port of the crystal to combine with the generated squeezed LO field. An enhancement of 0.7 dB (1.4 dB inferred) in signal-to-noise ratio beyond the shot-noise limit is directly observed for this new heterodyne detection scheme. Practical applications of proposed technique in laser radar systems are discussed.
A new scheme is described for the generation of pulsed squeezed light by use of femtosecond pulses that have been parametrically deamplified through a single pass in a thin (100-microm) potassium niobate crystal with a significant deamplification of approximately -3 dB. The quantum noise of each pulse is registered in the time domain by single-shot homodyne detection operated with femtosecond pulses; the best squeezed quadrature variance was 1.87 dB below the shot-noise level. Such a scheme provides a basic resource for time-resolved quantum communication protocols.
A new scheme is described for pulsed squeezed light generation using femtosecond pulses parametrically deamplified through a single pass in a thin (0.1mm) potassium niobate KNbO3 crystal, with a significant deamplification of about -3dB. The quantum noise of each individual pulse is registered in the time domain using a single-shot homodyne detection operated with femtosecond pulses and the best squeezed quadrature variance was measured to be 1.87 dB below the shot noise level. Such a scheme provides the basic ressource for time-resolved quantum communication protocols.
We experimentally demonstrate a novel sub-shot-noise-limited heterodyne detection scheme to measure a weak optical signal field by employing amplitude-squeezed light as the local oscillator (LO) field. The amplitude-squeezed LO field at 428.8 nm is generated from a high efficiency single-pass second-harmonic generation in a KNbO3{\mathrm{KNbO}}_{3}KNbO3​ crystal pumped by femtosecond (130 fs) pulses at 857.6 nm, and the signal field is combined with the generated squeezed LO field through the crystal. An enhancement of 0.7 dB (1.4 dB inferred) in signal-to-noise ratio beyond the shot-noise limit is directly observed.