Thomas Badr

Efficient cw operation of diode-pumped Nd:YLF lasers at 1312.0 and 1322.6 nm for a silver atom optical clock

Abstract We describe the efficient cw operation of two Nd:YLF lasers at 1312.0 and 1322.6 nm for the development of a silver atom optical clock. For a simple linear cavity laser configuration investigated at these wavelengths, we have obtained an output power of 3.6 W at 1312.0 nm for 13.8 W of absorbed pump power ( λ =806 nm) and 4.8 W output at 1322.6 nm with 16.3 W pump. At 1312.0 nm, using a twisted-mode cavity, a single-frequency output power of 750 mW has been obtained. Single-frequency operation (450 mW) at 1322.6 nm was achieved using an intra-cavity solid etalon.

Watt-level single-frequency tunable Nd:YLF/periodically poled KTiOPO 4 red laser

Intracavity second-harmonic generation of a diode-pumped Nd:YLiF(4) ring laser oscillating on the sigma-polarized (4)F(3/2) - (4)I(13/2) transition (lambda(omega) ~ 1314 nm) with a temperature-tuned periodically poled KTiOPO(4) (ppKTP) crystal is reported, yielding up to 0.92 W tunable (lambda(2omega) = 656-658 nm) single-frequency output. Evidence of self-mode-locking via cascading nonlinearities is observed when the ppKTP is strongly phase mismatched.

Transportable distance measurement system based on superheterodyne interferometry using two phase-locked frequency-doubled Nd:YAG lasers.

We describe a transportable distance measurement system based on synthetic wavelength interferometry. Two frequency-doubled Nd:yttrium aluminum garnet lasers at 532 nm are used to generate a synthetic wavelength of approximately 2.5 cm. A nonpolarizing interferometric system has been set up to eliminate polarization cross-talk issue. A superheterodyne detection was performed to measure the synthetic phase and to determine absolute distances. The capability to achieve fringe interpolation of 2pi/5600 has been demonstrated and an agreement in distance measurement at the 4 microm level has been achieved, compared to an optical interferometric 3 m long displacement bench.

Tunable Single-Frequency Nd:YVO

A record of 680-mW single-frequency red emission at 671.1 nm is demonstrated using a Nd:YVO4 ring laser intracavity frequency-doubled by a type-I critically phase-matched BiB3O6 crystal. Single-frequency tuning over ??red ~ 1.25 nm can be achieved with a thin etalon with reflectivity of 40%. At 1342.5 nm and with a T = 2% transmission output coupler, the laser provides an optimal 1.55 W of single-frequency power.

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This paper describes a transportable distance measurement system based on synthetic wavelength interferometry using two frequency-doubled Nd:YAG lasers. A non-polarizing system has been setup to eliminate polarization cross-talk issue. A partly software-implemented superheterodyne detection was performed to measure the synthetic phase. A fringe interpolation of 2π/5600 is demonstrated and an accuracy of ∼4 µm is achieved over 3 m.

BiB/

This paper describes a transportable distance measurement system based on synthetic wavelength interferometry using two frequency-doubled Nd:YAG lasers. To eliminate polarization crosstalk issue, a different system has been set up from those usually described in the literature. Indeed, we propose a system where the different beams are spatially separated instead of being polarization-separated. Furthermore, the superheterodyne detection is partly software-implemented to measure the synthetic phase, enabling an angular resolution of ~ 2π/5600 in the fringe pattern. A first assessment of the system has consisted in an indoor comparison on a 3-m-long displacement bench, successfully resulting in ~ 4 μm accuracy. Then, the system has been further modified for an indoor comparison over 25 m. Recent measurements are given, limited by now by the pitch angle of the displacement bench used for the comparison.

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This paper describes our project of an optical refractometer. The targeted accuracy for air index measurement is below 10−8. It is based on an optical resonator whose mechanical distortion as a function of pressure will be calibrated using helium gas.

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Using a Nd:YVO<inf>4</inf> ring laser and a type-I critically phase-matched BiBO crystal, a record 620 mW single-frequency red laser at 671.2nm is demonstrated. The laser is tunable over Δλ∼1.2nm around 671 nm.

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Recently, a continuous-wave (cw) diode-pumped intra-cavity frequency-doubled Nd:YLF ring laser oscillating on the σ-polarized transition (λ<inf>ω</inf>=1314nm) and employing a temperature-tuned periodically-poled KTP (ppKTP) nonlinear crystal has been reported to generate up to 0.92W single-frequency red output power [1]. When the ppKTP was strongly phase-mismatched, evidence of passive cascaded Kerr-lens mode locking (KLM) was inferred from a broad phase-coherent spectrum analyzed by a confocal Fabry-Perot interferometer. In this work, we demonstrate indeed that complex cascaded second-order nonlinear processes occurring inside the ppKTP crystal are responsible of the KLM operation of a π-polarized (λ<inf>ω</inf>=1321nm) Nd:YLF/ppKTP ring laser (Fig.1), over the full range of the ppKTP temperature tuning (15°C≪T≪75°C). While the ppKTP phase-matching temperature for the gain center wavelength occurs at T∼25–30°C (with a FWHM temperature bandwidth ΔT<inf>PM</inf>=10°C and spectral bandwidth Δλ<inf>PM</inf>=0.8nm for L=10mm), significant broadband (Δλ<inf>2ω</inf>≤1nm) red average power (≪100mW) is measured from intra-cavity SHG over the above full temperature variation. The preliminary analysis of the laser emission versus the ppKTP temperature or versus the intra-cavity power demonstrates unambiguously the tendency to cascaded KLM effects, which threshold occurs at about 5W of diode pump power. Mid-IR spectra recorded with an optical spectrum analyzer (OSA) reveal emission bandwidths greater than BW=3nm (Fig. 2) under the pulsing temporal regime, in correlation with a broadband background transmission from the scanning Fabry-Perot interferometer. Time traces recorded with a 10-GHz bandwidth InGaAs photodetector yield a periodic train of bi-colour sub-300ps pulses (instrumentation-limited) at the laser free-spectral range (c/L<inf>cav</inf>∼420 MHz or τ<inf>rep</inf>∼2.41ns). Further analysis of the pulsing features is under way. While passive KLM mode-locking due to pure cascaded second-order nonlinear effects was first reported in a GdVO<inf>4</inf>/ppKTP standing-wave cavity operating close to its stability region [2], our unidirectional ring laser operates well within the cavity stability range and is rather designed for cw operation. Such a mode-locked behaviour is never observed with a much broader spectral phase-matching bandwidth SHG crystals such as BiBO (Δλ<inf>PM</inf>=3.9nm) or LBO (Δλ<inf>PM</inf>=47nm).

Ring Laser at 671 nm

We report on the performance (watt‐level red output at ∼657 nm, long‐term passive single‐frequency operation and wavelength tuning over ∼4 nm) of an all solid‐state continuous‐wave Nd:YLiF4 (Nd:YLF) ring laser operating on the 4F3/2–4l13/2 σ‐polarized transition (λω = 1314 nm) and intra‐cavity frequency‐doubled by a temperature‐tuned periodically‐poled KTiOPO4 (ppKTP) crystal. Evidence of self‐mode‐locking via cascading second‐order nonlinearities is observed when the ppKTP is strongly phase‐mismatched on the Kerr‐lens focusing nonlinearity side. This red laser source is well suited for calcium and silver atom spectroscopy and cooling.