130 research outputs found
Experimental comparison of autodyne and heterodyne laser interferometry using a Nd:YVO4 microchip laser
Using a Nd:YVO4 microchip laser with a relaxation frequency in the megahertz
range, we have experimentally compared a heterodyne interferometer based on a
Michelson configuration with an autodyne interferometer based on the laser
optical feedback imaging (LOFI) method regarding their signal to noise ratios.
In the heterodyne configuration, the beating between the reference beam and the
signal beam is realized outside the laser cavity while in the autodyne
configuration, the wave beating takes place inside the laser cavity and the
relaxation oscillations of the laser intensity then play an important part. For
a given laser output power, object under investigation and detection noise
level, we have determined the amplification gain of the LOFI interferometer
compared to the heterodyne interferometer. LOFI interferometry is demonstrated
to show higher performances than heterodyne interferometry for a wide range of
laser power and detection level of noise. The experimental results are in good
agreement with the theoretical predictions
Sensitivity of synthetic aperture laser optical feedback imaging
In this paper we compare the sensitivity of two imaging configurations both
based on Laser Optical Feedback Imaging (LOFI). The first one is direct
imaging, which uses conventional optical focalisation on target and the second
one is made by Synthetic Aperture (SA) Laser, which uses numerical
focalisation. We show that SA configuration allows to obtain good resolutions
with high working distance and that the drawback of SA imagery is that it has a
worse photometric balance in comparison to conventional microscope. This
drawback is partially compensated by the important sensitivity of LOFI. Another
interest of SA relies on the capacity of getting a 3D information in a single
x-y scan
Nonlinear modification of the laser noise power spectrum induced by a frequency-shifted optical feedback
In this article, we study the non-linear coupling between the stationary
(i.e. the beating modulation signal) and transient (i.e. the laser quantum
noise) dynamics of a laser subjected to frequency shifted optical feedback. We
show how the noise power spectrum and more specifically the relaxation
oscillation frequency of the laser are modified under different optical
feedback condition. Specifically we study the influence of (i) the amount of
light returning to the laser cavity and (ii) the initial detuning between the
frequency shift and intrinsic relaxation frequency. The present work shows how
the relaxation frequency is related to the strength of the beating signal and
the shape of the noise power spectrum gives an image of the Transfer Modulation
Function (i.e. of the amplification gain) of the nonlinear-laser dynamics.The
theoretical predictions, confirmed by numerical resolutions, are in good
agreements with the experimental data.Comment: in Physical Review, American Physical Society (APS), 201
Deep and optically resolved imaging through scattering media by space-reversed propagation
We propose a novel technique of microscopy to overcome the effects of both
scattering and limitation of the accessible depth due to the objective working
distance. By combining Laser Optical Feedback Imaging (LOFI) with Acoustic
Photon Taging (APT) and Synthetic Aperture (SA) refocusing we demonstrate an
ultimate shot noise sensitivity at low power (required to preserve the tissues)
and a high resolution beyond the microscope working distance. More precisely,
with a laser power of 10mW, we obtain images with a micrometric resolution over
~8 transport mean free paths, corresponding to 1.3 times the microscope working
distance. Various applications such as biomedical diagnosis, research and
development of new drugs and therapies can benefit from our imaging setup
Limitations of synthetic aperture laser optical feedback imaging
In this paper we study the origin and the effect of amplitude and phase noise
on Laser Optical Feedback Imaging (LOFI) associated with Synthetic Aperture
(SA) imaging system. Amplitude noise corresponds to photon noise and acts as an
additive noise, it can be reduced by increasing the global measurement time.
Phase noise can be divided in three families: random, sinusoidal and drift
phase noise; we show that it acts as a multiplicative noise. We explain how we
can reduce phase noise by making oversampling or multiple measurements
depending on its type. This work can easily be extended to all SA systems
(Radar, Laser or Terahertz), especially when raw holograms are acquired point
by point
Coherent microscopy by laser optical feedback imaging (LOFI) technique
The application of the non conventional imaging technique LOFI (Laser Optical
Feedback Imaging) to coherent microscopy is presented. This simple and
efficient technique using frequency-shifted optical feedback needs the sample
to be scanned in order to obtain an image. The effects on magnitude and phase
signals such as vignetting and field curvature occasioned by the scanning with
galvanometric mirrors are discussed. A simple monitoring method based on phase
images is proposed to find the optimal position of the scanner. Finally, some
experimental results illustrating this technique are presented
Synthetic aperture laser optical feedback imaging using a translational scanning with galvanometric mirrors
In this paper we present an experimental setup based on Laser Optical
Feedback Imaging (LOFI) and on Synthetic Aperture (SA) with translational
scanning by galvanometric mirrors for the purpose of making deep and resolved
images through scattering media. We provide real 2D optical synthetic-aperture
image of a fixed scattering target with a moving aperture and an isotropic
resolution. We demonstrate theoretically and experimentally that we can keep
microscope resolution beyond the working distance. A photometric balance is
made and we show that the number of photons participating in the final image
decreases with the square of the reconstruction distance. This degradation is
partially compensated by the high sensitivity of LOFI
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