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Quantum Electronics and Laser Science Conference

Quantum-noise measurements in high efficiency single-pass sum-frequency generation with femtosecond pulses

Yongqing Li, Dorel Guzun, Min Xiao

Published Jan 20, 2003• 0 citations
Publisher

Abstract

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.

DOI
10.1109/qels.1999.807113

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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.
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.
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.
Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ±\pm± 50 nm for the generation of bright squeezed light at 472~nm ±\pm± 4~nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2\pm0.2±0.2)~dB 1064 nm vacuum squeezed state is converted to a 1.6($\pm0.2) dBtunablebrightbluesqueezedstate.Wefurthermoredemonstratesimultaneousfrequency−andspatial−modeconversionofthe1064−nmvacuumsqueezedstate,andmeasure1.1(0.2)~dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1(0.2) dBtunablebrightbluesqueezedstate.Wefurthermoredemonstratesimultaneousfrequency−andspatial−modeconversionofthe1064−nmvacuumsqueezedstate,andmeasure1.1(\pm0.2) dBand0.4(0.2)~dB and 0.4(0.2) dBand0.4(\pm0.2) dBofsqueezingintheTEM0.2)~dB of squeezing in the TEM0.2) dBofsqueezingintheTEM_{01}$ and TEM02_{02}02​ modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.
Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ± 50 nm for the generation of bright squeezed light at 472 nm ± 4 nm, currently limited by the phase-matching of the used nonlinear crystal. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2) dB 1064 nm vacuum squeezed state is converted to a 1.6(±0.2) dB tunable bright blue squeezed state. We furthermore demonstrate simultaneous frequency- and spatial-mode conversion of the 1064-nm vacuum squeezed state, and measure 1.1(±0.2) dB and 0.4(±0.2) dB of squeezing in the TEM01 and TEM02 modes, respectively. With further development, we foresee that the source may find use within fields such as sensing, metrology, spectroscopy, and imaging.
Quantum frequency conversion, the process of shifting the frequency of an optical quantum state while preserving quantum coherence, can be used to produce non-classical light at otherwise unapproachable wavelengths. We present experimental results based on highly efficient sum-frequency generation (SFG) between a vacuum squeezed state at 1064 nm and a tunable pump source at 850 nm ± 50 nm for the generation of bright squeezed light at 472 nm ± 4 nm. We demonstrate that the SFG process conserves part of the quantum coherence as a 4.2(±0.2) dB 1064 nm vacuum squeezed state is converted to a 1.6(±0.2) dB tunable bright blue squeezed state.
We propose non-phase-matched sum frequency generation (SFG) as a method for characterizing broadband multimode light. Both the central wavelength and the bandwidth are in this case not limited by the phase matching condition. As an example, we consider bright squeezed vacuum (BSV) generated through high-gain parametric down conversion (PDC). In the spectrum of SFG from BSV, we observe the coherent peak and the incoherent background. We show that the ratio of their widths is equal to the number of frequency modes in BSV, which in the case of low-gain PDC gives the degree of frequency entanglement for photon pairs. By generating the sum frequency in the near-surface region of a nonlinear crystal, we increase the SFG efficiency and get rid of the modulation caused by chromatic dispersion, known as Maker fringes. This allows one to use non-phasematched SFG as a wavelength-independent autocorrelator. Furthermore, we demonstrate efficient non-phase-matched three- and four-frequency summation of broadband multimode light, hardly possible under phase matching. We show that the latter contains the coherent peak while the former does not.