We evaluate a dual-frequency and dual-polarization optically-pumped semiconductor laser emitting at 852 nm as a new laser source for compact atomic clocks based on the coherent population trapping (CPT) technique. The frequency difference between the laser modes is tunable to 9.2 GHz corresponding to the ground state hyperfine-split of Cs. Impact of the laser noise has been investigated. Laser relative intensity noise is limited by the pump-𝑅𝐼𝑁 transfer to a level of - 110 dB/Hz. Laser frequency noise shows excess mechanical and technical noise resulting in a laser linewidth of 1 MHz at 1 s in lock operation. The noise performance and spectral properties of the laser are already adequate to realize CPT experiments and should result in Allan standard-deviation of the clock below 1 × 10-12 at 1 second.
Coherent population trapping (CPT) is an interesting technique for the development of compact atomic frequency references. We describe an innovating laser source for the production of the two cross-polarized coherent laser fields which are necessary in CPT-based atomic clocks. It relies on the dual-frequency and dual-polarization operation of an optically-pumped vertical external-cavity semiconductor laser. This particular laser emission is induced by intracavity birefringent components which produce a controllable phase anisotropy within the laser cavity and force emission on two cross-polarized longitudinal modes. The laser emission is tuned at the Cs D2 line (λ = 852.14 nm), and the frequency difference Δν between the two laser modes is tunable in the microwave range. The laser line wavelength is stabilized onto an atomic hyperfine transition, and concurrently the frequency difference is locked to an ultra-low noise RF oscillator at 9.2 GHz. The high spectral purity of the optically-carried microwave signal resulting from the beatnote of the two cross-polarized laser lines is assessed through its narrow spectral linewidth (<30 Hz) as well as its low phase noise (≤ -100 dBrad2/Hz). The performance of this laser source is already adequate for the interrogation of atoms in a CPT atomic clock, and should result in an estimated relative stability of 3.10-13τ-1/2 – one order of magnitude better than commercial atomic clocks.
We investigate, both experimentally and theoretically, the spectral behavior of the intensity noises as well as the phase noise of the radio frequency (RF) beatnote generated by optical mixing of two orthogonally polarized modes of a dual-frequency VECSEL. To be more speci c, we measure the relative intensity noises (RINs) and the correlation between the intensity noises of the two laser modes for di erent nonlinear coupling strengths between them within frequencies 10 kHz to 50 MHz. Moreover for these frequencies, we explore the spectral behavior of the phase noise of the RF beatnote generated by optical mixing of two laser modes and the dependence of this RF phase noise spectrum on the strength of non-linear coupling between the laser modes. The theoretical model considers pump intensity uctuations as the only source of noise within the considered frequency range. The pump uctuations, entering into the two spatially separated laser modes on the active medium, are measured to be white noises of identical amplitudes, partially correlated, and in phase. To model the RF phase noise, we take into account two di erent physical mechanisms: (i) the coupling of intensity noise with phase noise due to large Henry factor of the semiconductor gain medium and (ii) the thermal uctuations of the refractive index of the semiconductor active medium induced by pump intensity uctuations. For all the results, theory shows very good agreement with the experiment.
We present the stabilization of the beatnote of an Er,Yb:glass Dual Frequency Laser at 1.53 μm with optical fiber delay
lines. Instead of standard optoelectronics oscillators, this architecture does not need RF filter and offers a wide tunability
from 2.5 to 5.5 GHz. Thank to a fine analysis of the laser RIN to phase noise conversion in the photodiodes, the expected
RF-amplifiers noise limit is reached with a phase noise power spectral density of -25 dBc/Hz at 10 Hz (respectively -110
dBc/Hz at 10 kHz) from the carrier over the whole tuning range. Implementation of a double fiber coil architecture
improves the oscillator spectral purity: the phase noise reaches a level of -35 dBc/Hz at 10 Hz (respectively -112 dBc/Hz
respectively 10 kHz) from the carrier.
We present here a widely tunable opto-electronic oscillator (OEO) based on an Er,Yb:glass Dual Frequency Laser (DFL)
at 1.53 μm. The beatnote is stabilized with an optical fiber delay line. Compared to classical optoelectronic oscillators,
this architecture does not need RF filter and offers a wide tunability. We measured a reduction of 67 dB of the phase
noise power spectral density (PSD) at 10 Hz of the carrier optical fiber leading to a level of -27 dBc/Hz with only 100 m
optical fiber. Moreover, the scheme offers a microwave signal tunability from 2.5 to 5.5 GHz limited by the RF
components.
We report on a wideband lidar-radar architecture in which range resolution is independent of pulse duration thanks to the
use of a widely tunable intensity-modulated laser combined with a radar-like signal processing. We use a dual frequency
laser which provides a modulated beam with a modulation frequency tunable over 1 GHz. A stepped-frequency
waveform is obtained and 30 cm range resolution is demonstrated. Field experiments have been conducted on mobile
targets, which assess the ability of this setup to measure simultaneously the range and the velocity. A velocity resolution
of 1.70 m/s is demonstrated.
We report on a wideband lidar-radar architecture in which range resolution is independent of pulse duration thanks to the
use of a widely tunable intensity-modulated laser combined with a radar-like signal processing. As a source, we use a
dual-frequency laser which provides a 100 % depth intensity modulated beam at GHz frequencies. The frequency is
electrically adjustable over 1 GHz and is stabilized with a fiber-loop based frequency discriminator. With this setup, we
generated a 1 GHz bandwidth stepped-frequency waveform. A range resolution of 22 cm is demonstrated.
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