Laser Cooler Research Articles

Phonon‐Assisted Anti‐Stokes Fluorescence of an Yb3+‐Doped Oxide Glass: Phononics and Spectroscopic Analysis of Its Prospects as Solid‐State Laser Cooler

Phonon‐assisted anti‐Stokes fluorescence is observed in an Yb3+ doped, 30 mol% BaO containing tellurite glass for the first time. Absorption, excitation, and the anti‐Stokes fluorescence spectra of the glass show a phonon progression of 150 cm−1. The phonon is identified as the combined vibrational mode of rocking of the nonbridging oxygen atoms of both TeO3− and its dimer Te2O52− units and the bending of the Te–O–Te linkage of the Te2O52− units of the glass structure. These units are known to exist in plenty in such BaO–TeO2 glasses with high BaO content. Association of the phonon modes with the absorption and anti‐Stokes fluorescence spectra of Yb3+ of the glass, strongly suggests that the phonon is coupled both with the 2F7/2(1) ground and the 2F5/2(5) excited states of the ion; and the observed anti‐Stokes fluorescence originates through annihilation of the excited state manifolds of this coupled phonon. Phononics and spectroscopic analysis of the anti‐Stokes fluorescence process suggest that the material should be prospective for use as solid‐state laser cooler.

Impacts of laser cooling for low earth orbit observation satellites: An analysis in terms of size, weight and power

Laser cooling in solids is a breakthrough technology allowing vibration-free cooling down to a temperature of 100 K in a miniaturized way. It appears as a promising technology to improve future observation satellites performances e.g. in SWIR and NIR domains.In this paper, integration of a laser cooler onboard an observation satellite is studied for the first time. Our study focuses on size, weight and power (SWaP) criteria, at both satellite payload and platform levels. Its goal is to assess the interest of using an optical cryocooler over a mechanical cryocooler for low earth orbit (LEO) infrared observation missions.A preliminary space-borne laser cooler (LC) architecture is proposed. It is composed of two parts. The first part is the cooling head, based on state-of-the-art cooling crystals 10%Yb:YLF and an astigmatic multipass cavity. The second part is the cryocooler opto-electronics, based on redundant laser diodes and fiber coupled to the cooling head. The cooling power is estimated for a small focal plane, taking into account the thermal load of an infrared detector and the parasitic heat fluxes inside the cryostat. The required optical and electrical powers of the laser cooler are then estimated considering the crystal efficiency, the thermal link losses and the opto-electronics efficiency.Assuming a 5-year long LEO microsatellite mission, the sizing of the electrical power systems (PCDU, solar array, batteries) and thermal control systems (heatpipes, radiators) is performed. An additional mass margin is added to take mechanical support structures into account. At the end, payload and platform masses and volumes are summed respectively to obtain a SWaP balance at satellite level, representative of the overall impact of a laser cooler. The study is repeated for the case of a Miniature Pulse Tube Cooler (MPTC) architecture under the same mission and platform assumptions. Finally, the two architectures are compared. It is shown that even if the power requirement of a laser cooler is high, the reduction of mass and internal volume makes it possible for small satellite payloads.

Accumulating laser-coolable ions in a linear Paul trap for ultrahigh-density beam dynamics experiment

An ion plasma confined in a linear Paul trap (LPT) exhibits the dynamic behavior physically equivalent to that of a charged-particle beam in an alternating-gradient (AG) transport channel. The Simulator of Particle Orbit Dynamics (S-POD) is a compact apparatus designed on the basis of this fact for diverse beam-physics experiments. We have so far employed Ar+ ions that can readily be produced from neutral Ar gas atoms through the electron bombardment process. A space-charge-induced tune shift of up to about 20% of the bare tune can be achieved in Ar+ plasmas. We are now preparing for future S-POD experiment to explore even higher beam-density regions. For this purpose, a large number of Ca+ ions need to be stored in the LPT. Since S-POD is equipped with a powerful laser cooler for Ca+, the use of this ion species vastly expands the density range we can survey. The production of an intense bunch of Ca+ ions is, however, not so easy because of some technical reasons. By optimizing the operating condition of a multi-sectioned LPT, we succeeded in increasing the number of accumulated Ca+ ions to the level comparable to Ar+ ion plasmas. This paper reports on updated results of the experiment.

Phonon-Assisted Anti-Stokes Lasing in ZnTe Nanoribbons.

Phonon-assisted anti-Stokes emission and its stimulated emission in polar semiconductor ZnTe are demonstrated via the annihilation of phonons as a result of strong exciton-phonon coupling. The findings are not only important for developing high-power radiation-balanced lasers, but are also promising for manufacturing ultraefficient solid-state laser coolers.

Design and fabrication of a linear Paul trap for the study of space-charge-dominated beams

The collective motion of a single-species plasma in a radio-frequency quadrupole trap is physically almost equivalent to that of a charged-particle beam propagating through a periodic magnetic lattice. This fact suggests that one can experimentally study the behavior of space-charge-dominated beams by using a compact table-top device. At Hiroshima University, a Paul trap system dedicated to beam-physics purposes has been designed and is now under construction. Controllable, pulsed radio-frequency voltages, instead of ordinary sinusoidal voltages, are applied to the trap electrodes such that collective beam dynamics in various lattice structures can be explored. The system is equipped with a laser cooler that enables us to adjust the tune depression of a Ca+ plasma. In this paper, the basic design concept of the trap and the detailed system configuration are presented.

Ultra-low Emittance Beam Generator Using Coulomb Crystals

Ultra-low Emittance Beam Generator Using Coulomb Crystals

Distributed laser refrigeration

A 250-mum-diameter fiber of ytterbium-doped ZBLAN (fluorine combined with Zr, Ba, La, Al, and Na) has been cooled from room temperature. We coupled 1.0 W of laser light from a 1013-nm diode laser into the fiber. We measured the temperature of the fiber by using both fluorescence techniques and a microthermocouple. These microthermocouple measurements show that the cooled fiber can be used to refrigerate materials brought into contact with it. This, in conjunction with the use of a diode laser as the light source, demonstrates that practical solid-state laser coolers can be realized.