KEYWORDS: Tunable lasers, Diodes, Signal to noise ratio, Laser amplifiers, High power lasers, Continuous wave operation, Laser development, Fiber lasers
Our work demonstrated a tunable Polarization Maintaining (PM) thulium-doped fiber two stages amplifier system spanning the 1820–1880nm range with a fiber-coupled output power as high as 30W CW. In addition, the high-power booster stage is made using double clad fibers pumped with 793nm laser diodes wich contrasts with the usual core-pumping using Erbium-Ytterbium laser sources emitting around 1570nm. To the best of our knowledge, this marks the first reported demonstration of a 30W level all-fiber PM TDFA Master Oscillator Power Amplifier (MOPA) operating within the 1820–1880nm wavelength regime. The significance of this achievement extends to a wide array of applications, including but not limited to quantum computing.
High power amplification of an electro-optic frequency comb to 200W is achieved, featuring sub 500 fs pulses over a widely tunable repetition rate in the 1-18 GHz range. The final amplification stage of the monolithic set-up includes a full-silica large-mode-area microstructured polarization-maintaining ytterbium-doped fiber with a mode field diameter of 24 µm and M2 -parameter values below 1.1. Pulse durations as low as 192 fs were recorded from output pickoff compression.
We present here the development of ultra-low NA large mode area neodymium doped alumino-phospho-silica fibers with different clad-to-core ratios for high power laser emission around 910nm. This ratio is determinant in the competition between the 3-level transition at 910nm and 4-level transition of neodymium at 1060nm. The study shows that the 30/130µm (core/cladding) fiber was the most efficient, with a record output power of 83W at 910nm, yielding a 47% slope efficiency and a good beam quality (M²~1.5). Parasitic power at 1060nm was kept lower than 1W and no sign of roll-off was observed at maximum pump power.
We present in this work, the development of a nanosecond pulsed Master-Oscillator Power-Amplifier (MOPA) laser system near 905 nm based on the 3-level transition of Neodymium using a novel low NA polarization-maintaining Nd-doped silica fiber with a 30µm core and 130µm cladding. The MOPA delivered up to 24 W of average power (0.6 mJ energy per pulse) with good beam quality (M²~1.4). Cascaded LBO and BBO crystals are used respectively for second-harmonic generation and fourth-harmonic generation, giving respectively average output powers of 4.9W at 452nm (conversion efficiency of 20%) and 550mW at 226nm (conversion efficiency of 10%).
We investigate femtosecond pulse generation from a CW Laser diode by optical gating with a Mach-Zehnder electro-optic modulator. 45 ps pulses are amplified to ten’s of watt peak power and propagated through a standard polarization maintaining fiber to reach enough spectral broadening by self-phase-modulation. Pulses are then compressed down to about 500 femtoseconds with a grating compressor. We analyse the measured spectral broadening with respect to pulse repetition rate and average power and do some comparison with numerical simulations. This approach paves the way to versatile ultrashort pulse Lasers that could be easily synchronized.
A single-frequency blue laser at 461 nm is generated by frequency doubling an amplified diode laser operating at 922 nm via a LBO crystal placed in an ultra-compact resonant linear cavity. The best optical conversion efficiency achieved by the setup is 87% which gives more than 1 W of power in the blue. The frequency-converted beam is characterized in terms of long-term power stability, residual intensity noise, hysteresis induced by the input power stability, and geometrical shape. The generated 461 nm radiation can be used to obtain a magneto-optical trap on strontium 5s21S0 – 5p1 P1 transition.
This paper, “Un projet d'horloge atomique spatiale utlilsant le refroidissement des atomes par faisceaux laser: PHARAO," was presented as part of International Conference on Space Optics—ICSO 1997, held in Toulouse, France.
We have developed a Watt-level single-frequency tunable fiber laser in the 915-937 nm spectral window. The laser is based on a neodymium-doped fiber master oscillator power amplifier architecture, with two amplification stages using a 20 mW extended cavity diode laser as seed. The system output power is higher than 2 W from 921 to 933 nm, with a stability better than 1.4% and a low relative intensity noise.
High power single frequency lasers are very attractive for a wide range of applications such as nonlinear conversion, gravitational wave sensing or atom trapping. Power scaling in single frequency regime is a challenging domain of research. In fact, nonlinear effect as stimulated Brillouin scattering (SBS) is the primary power limitation in single frequency amplifiers. To mitigate SBS, different well-known techniques has been improved. These techniques allow generation of several hundred of watts [1]. Large mode area (LMA) fibers, transverse acoustically tailored fibers [2], coherent beam combining and also tapered fiber [3] seem to be serious candidates to continue the power scaling. We have demonstrated the generation of stable 200W output power with nearly diffraction limited output, and narrow linewidth (Δν<30kHz) by using a tapered Yb-doped fiber which allow an adiabatic transition from a small purely single mode input to a large core output.
Photonic synthesis of radio frequency waveforms revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. In this contribution, we will present a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. We will show the generation of the purest microwave signal with a fractional frequency stability below 6.5×10-16 at 1 s and a timing noise floor below 41 zs Hz-1/2 (phase noise below -173 dBc Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurements methods developed here can benefit the characterization of a broad range of signals.
Residual timing noise from two synchronized diode pumped solid-state ytterbium-doped ultrafast laser oscillators is investigated. The lasers are passively mode-locked with a SESAM, which allows self-starting and stable laser operation coupled to a robust and cost-efficient design. A balanced optical cross-correlator is used to synchronize the laser repetition rates and to characterize their residual timing noise. The timing jitter measurement resolution is 8as and is limited by the cross-correlator photocurrent shot-noise. The integrated residual timing jitter is estimated to 73 as from 10 kHz to 31 MHz offset frequency. The timing jitter performance is limited by intracavity amplitude-noise-to-timing-noise conversion, mostly attributed to the SESAM. The timing jitter amounts to 4:5 fs when integrated from 10 Hz to 31 MHz because of excess technical noise contribution. This performance already makes the tested laser oscillator suitable for challenging time-resolved experiments setups.
Lasers with sub-hertz line-width and fractional frequency instability around 1×10-15 for 0.1 s to 10 s averaging time are currently realized by locking onto an ultra-stable Fabry-Perot cavity using the Pound-Drever-Hall method. This powerful method requires tight alignment of free space optical components, precise polarization adjustment and spatial mode matching. To circumvent these issues, we use an all-fiber Michelson interferometer with a long fiber spool as a frequency reference and a heterodyne detection technique with a fibered acousto optical modulator (AOM)1. At low Fourier frequencies, the frequency noise of our system is mainly limited by mechanical vibrations, an issue that has already been explored in the field of optoelectronic oscillators.2,3,4
We have demonstrated the feasibility of a free-space ultra-stable optical link on a 3 meters test bench, operating at 100 MHz. With this type of link, it is possible to transfer a 100 MHz signal with a relative frequency stability of a few 10−14 at one second integration time, 10−16 at one day and a phase stability of a few picoseconds per day in presence of moderate mechanical vibrations and thermal fluctuations.
The comparisons of modern clocks of distant (<100 km) Time and Frequency laboratories have a strong scientific interest. In this context we study a low noise frequency distribution via optical fibres. Some preliminary tests have been realized and the results are encouraging. We expect to transfer ultra stable oscillators with a relative frequency stability of a few 10−14 at one second integration time, 10−16 at one day.
R. Nyman, G. Varoquaux, J.-F. Clement, P. Bouyer, G. Santarelli, F. Pereira Dos Santos, A. Clairon, A. Landragin, D. Chambon, F. Lienhart, S. Boussen, A. Bresson
We present our the construction of an atom interferometer for inertial sensing in microgravity, as part of the I.C.E. (Interferometrie Coherente pour l’Espace) collaboration. On-board laser systems have been developed based on fibre-optic components, which are insensitive to mechanical vibrations and acoustic noise, have sub-MHz linewidth, and remain frequency stabilised for weeks at a time. A compact, transportable vacuum system has been built, and used for laser cooling and magneto-optical trapping. We will use a mixture of quantum degenerate gases, bosonic 87Rb and fermionic 40K, in order to find the optimal conditions for precision and sensitivity of inertial measurements. Microgravity will be realised in parabolic flights lasting up to 20s in an Airbus.
We report the main characteristics and performances of the first – to our knowledge – prototype of an ultra-stable cavity designed and produced by industry with the aim of space missions. The cavity is a 100 mm long cylinder rigidly held at its midplane by an engineered mechanical interface providing an efficient decoupling from thermal and vibration perturbations. The spacer is made from Ultra-Low Expansion (ULE) glass and mirrors substrate from fused silica to reduce the thermal noise limit to 4x10-16. Finite element modeling was performed in order to minimize thermal and vibration sensitivities while getting a high fundamental resonance frequency. The system was designed to be transportable, acceleration tolerant (up to several g) and temperature range compliant [-33°C; +73°C]. The axial vibration sensitivity was evaluated at 4x10-11 /(ms-2), while the transverse one is < 1x10-11 /(ms-2). The fractional frequency instability is < 1x10-15 from 0.1 to few seconds and reaches 5-6x10-16 at 1s.
We report a high performance, fully monolithic 40 μm core, Yb-doped photonic crystal fiber amplifier module. The developed fused combiner allows us to couple 6 pumps of 50 W at 976 nm and 5 W of signal at 1064 nm in the PCF amplifier. We then produced up to 210 W of average power at 1064 nm which is the highest power ever delivered by a fully monolithic PCF amplifier. The module is entirely thermally controlled in a rugged package, and has run more than 25 days at > 100W average power with an excellent peak to peak power stability < 1%.
Olivier Lopez, Nicola Chiodo, Fabio Stefani, Fabrice Wiotte, Nicolas Quintin, Anthony Bercy, Christian Chardonnet, Giorgio Santarelli, Paul-Eric Pottie, Anne Amy-Klein
The transfer of ultra-stable frequencies between distant laboratories is required by many applications in time and frequency metrology, fundamental physics, particle accelerators and astrophysics. Optical fiber links have been intensively studied for a decade and brought the potential to transfer frequency with a very high accuracy and stability thanks to an active compensation of the propagation noise. We are currently developing an optical metrological network using the fibers of the French National Research and Education Network. Using the so-called dark-channel approach, the ultrastable signal is copropagating with data traffic using wavelength division multiplexing. Due to significant reflections and losses along the fibers, which cannot be compensated with amplifiers, we have developed some repeater stations for the metrological signal. These remotely-operated stations amplify the ultrastable signal and compensate the propagation noise. The link is thus composed of a few cascaded spans. It gives the possibility to increase the noise correction bandwidth, which is proportional to the inverse of the fiber length for each span. These stations are a key element for the deployment of a reliable and large scale metrological network. We report here on the implementation of a two-spans cascaded link of 740 km reaching a relative stability of a few 10-20 after 103 s averaging time. Extension to longer links and alternative transfer methods will be discussed.
Experiments of transmission of sub-Hz cavity-stabilized 1542 nm laser frequency using a pair of 43 km dark fibers in
urban environment are reported on successively 86 km and 172 km, with fractional frequency instability in the 10-19
range. A new approach is then introduced consisting in using part of an optical telecommunications network carrying
simultaneously data traffic using a DWDM scheme to multiplex the metrological signal. This method is experimentally
implemented using 22 km of fiber linking Université Paris 13 to its internet access point without degradation of the link
instability. We finally present a project of large scale link between Paris and the German border using RENATER
network which could constitute the first step of the building of a European optical network for ultrastable frequency dissemination and comparison.
KEYWORDS: Clocks, Time metrology, Cesium, Space operations, Laser metrology, Picosecond phenomena, Frequency metrology, Microwave radiation, Data communications, Power supplies
The ACES (as Atomic Clock Ensemble in Space) mission, managed by the European Space Agency, has three
main objectives. The first one deals with the operation and study of the laser cooled cesium clock PHARAO
(as Projet d'Horloge Atomique à Refroidissement d'Atomes en Orbite) to reach a frequency accuracy of 10-16
in space. The second one is to perform fundamental metrology by comparing the clock signal with ground based
clocks via a two way time transfer link. The third one is to perform fundamental physics tests such as a new
measurement of the red shift at 2 parts per million and a search for variations of fundamental physical constants.
The expected time transfer resolution is 0.3 ps at 300 seconds and 7 ps per day. An H-maser developed by the
Observatoire Cantonal de Neuchatel is the second ACES clock and will be used as a stable frequency reference
for mid term duration. We give an overview of the ACES mission and its operation and present the first results
obtained with the engineering model of the laser cooled cesium clock PHARAO. This model is first developed to
validate the flight model design.
We report on the evaluation of an optical lattice clock using fermionic 87Sr. The measured frequency of the
1S0 → 3P0 clock transition is 429 228 004 229 873.7Hz with a fractional acuracy of 2.6 × 10-15. This evaluation
is performed on mF = ±9/2 spin-polarized atoms. This technique also enables to evaluate the value of the
differential Landé factor, 110.6Hz/G. by probing symmetrical σ-transitions.
The use of diode lasers to cool and trap Cesium atoms in a low Cs pressure cell allows the construction of a relatively simple and reliable atomic fountain frequency standard. Here we discuss the design and the potentialities of the Cs clock frequency standards being built at L.P.T.F..
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