No abstract

Li, Guzun, and Xiao Reply: The conclusion (no improvement in signal-to-noise ratio in our experiment [1]) made by Ralph [2] was based on Eqs. (1) and (2) in the Comment. As indicated by the Comment, these equations were derived for a system of intracavity second harmonic generation (SHG) with a cw pumping beam, which is very different from our experimental situation. Our experiment was done in a single-pass type-I phase-matched SHG with femtosecond pulses (the frequency width of the laser pulses is much broader than the phase-matching width of the nonlinear crystal). The Comment uses a cavity with cw input and assumes that "this does not change the physics of the setup, provided we consider only frequencies well within the cavity linewidth." However, this is definitely not suitable to our experimental situation in which 100 fs pulses (frequency spectral width about 10 nm, which is much, much larger than any reasonable cavity linewidth), were used. We have checked the model used in Ref. [3] [which gives Eq. (1) and (2) of the Comment] and the existing theoretical treatments of the traveling-wave SHG. We conclude that the theoretical model used in the Comment can not be directly applied to our experimental situation. For example, the theoretical calculation on which the Comment was based cannot explain the classical SHG efficiency curve and squeezing behaviors in our experimental situation [4].The main argument of the Comment is that the weak blue signal amplitude (classically averaged component) should be reduced by the SHG process as the system reduces the quantum fluctuations in the generated blue LO field. The Comment claimed that its Eq. (1) is based on Refs. [2][3][4]. However, the published Refs.[2] and [3] in the Comment discuss how the pump noises (in fundamental field) transfer to the harmonic field and assume a vacuum input at the harmonic frequency. They did not discuss how the classical component transfers, as in the case of our experiment. So, the argument of the Comment is based solely on an unpublished Ph.D thesis [3] that treats the classical component in the same way as the quantum noise components. To our knowledge, so far there is no experimental evidence showing that the classical sideband component in blue field is reduced by the SHG process.We disagree with the Comment on treating the classical component in the same way as the quantum noise components and believe that Eq. (2) in the Comment is oversimplified. We do not believe that the weak input blue signal light (at 17.5 MHz from the second harmonic frequency) participates in the nonlinear process in the crystal (at least not in the same level we are considering here). If the input blue signal participates in the nonlinear interaction, accord-

Articles you may be interested inHigh sensitivity and multifunctional micro-Hall sensors fabricated using InAlSb/InAsSb/InAlSb heterostructures J. Appl. Phys. 105, 07E909 (2009); 10.1063/1.3074513 Detection of magnetically labeled DNA using pseudomorphic AlGaAs ∕ InGaAs ∕ GaAs heterostructure micro-Hall biosensors J. Appl. Phys. 99, 08P103 (2006); 10.1063/1.2162041 Doped-channel micro-Hall devices: Size and geometry effects J. Appl. Phys. 98, 094503 (2005); 10.1063/1.2128472Second-generation quantum-well sensors for room-temperature scanning Hall probe microscopy Micro-Hall devices based on modulation-doped Al 0.12 In 0.88 Sb/ InSb heterostructures are fabricated and studied in terms of sensitivity and noise. Extremely high supply-current-related magnetic sensitivities of 1800 V A −1 T −1 at 77 K and 1220 V A −1 T −1 at 300 K are reported and observed to be independent of the bias current. The detection limit of the devices studied at low and room temperature are at nanotesla values throughout the broad frequency range from 20 Hz to 20 kHz. The low detection limit of 28 nT at 300 K and 18 nT at 77 K were found at high frequencies where the Johnson noise is dominant. A measured detection limit per unit device width of 630 pT mm Hz −1/2 is reported indicating the potential for picotesla detectivity.

Crossed transitions between the wetting layer valence band and the quantum dot (QD) electron states are revealed in the photoluminescence from self-assembled In0.4Ga0.6As∕GaAs QDs. The strength of these transitions becomes comparable with the excitonic transitions for below-GaAs barrier excitation and decreases significantly with below wetting layer excitation. The observed peculiar QD photoluminescence dependences on temperature and excitation density are due partly to interdot carrier transfer through the continuum states related to the wetting layer morphology and to phonon-assisted processes.

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 KNbO 3 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. [S0031-9007(99)09410-7]