LNA Laser Research Articles

Femtosecond Self-Mode-Locked La1-xMgNdxAl11O19 Laser Pumped by a Laser Diode

A laser-diode-pumped self-mode-locked La1-xMgNdxAl11O19 laser has been demonstrated. Transform-limited pulses of 631 fs duration have been generated from the laser, which corresponds to a spectral width of 2.03 nm. The time-bandwidth product and average output power were 0.34 and 11 mW, respectively. Characteristic parameters of the LNA laser, such as the stability, the strength of the self-mode-locking, and the change of beam spot size with intracavity normalized power have been calculated and optimized. The theoretical simulation results are in good agreement with the experiments.

Study of the metastable helium spin polarization in an optically pumped afterglow

A very efficient technique of optical pumping is applied in order to polarize 2 3S 1 metastable 4He atoms within an afterglow by means of a high power LNA laser. An almost complete atom polarization is achieved. This allows the production of an electron beam of appreciable intensity with high polarization well suited to perform a polarized electron source for linear cw accelerators.

Laser frequency stabilization using Zeeman effect

We describe a new and easy to handle method to stabilize the laser frequency on an atomic transition. This method, based on Zeeman effect, involves the circular dichroism of an atomic vapour submitted to a magnetic field. It is applied to the frequency stabilization of a single frequency LNA laser on (2 (2 3S1-2 3P0) helium transition.

Continuous wave, Q-switched and mode-locked operation of a laser-pumped Nd:LNA laser

A linear cavity Nd:LNA laser pumped by a Ti:sapphire laser was investigated in a continuous wave (CW), Q-switched and mode-locked regime. A parallel study using a Nd:YAG crystal was also conducted using the same optics and intercavity elements. The slope efficiencies obtained with a 5% output coupler in CW operation are 41 and 55% for Nd:LNA ( lambda approximately 1.054 nm) and Nd:YAG ( lambda approximately 1.065 nm), respectively. Mode locking was achieved with a 360-MHz intracavity phase modulator and led to a relative improvement of the Nd:LNA versus the Nd:YAG device. In the Q-switched mode with an intracavity acoustooptic modulator, the performance of the two lasers is almost identical. With 300 mW of absorbed pump power at lambda approximately 800 nm, peak powers approximately 130 W were achieved in a 65-ns pulse with a 5% output coupler.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A dense polarized 3He target based on compression of optically pumped gas

3He-gas is spin polarized by the method of optical pumping of metastables and metastability exchange in a low pressure gas discharge. At a pressure of p ≈ 1.5 Torr a volume of 1 l is polarized within about 30 s to a degree of 50% with 300 mW of incident light from an argon-ion laser pumped LNA laser, tuned to the λ = 1.083 μm resonance line. The polarized gas is compressed by a Toepler pump into a target cell of 120 cm 3 volume. In a first attempt a steady state polarization of 30% has been achieved in the target at a pressure of 685 Torr. The paper analyses the essential parameters governing this technique and pilotes its experimental realization.

Accurate optical measurement of nuclear polarization in optically pumped 3He gas

Large nuclear polarizations M (over 80 %) can now be achieved in gaseous 3He by optical pumping. The gas is excited by an RF discharge and is oriented using a high power LNA laser which is lamp pumped and tuned to the 2 3S-2 3P transition at 1.08 μm. In this paper we describe an experiment in which we measure M with high absolute precision. Our method is based on a change as a function of M in the ratio of σ or π polarized light absorbed from a weak probe beam by the 2 3S metastable atoms. The probe was delivered by a diode pumped LNA laser and propagated perpendicular to the direction of the magnetization. Simultaneous measurement of M was made by monitoring the degree of circular polarization $\cal{P}$ of the optical line at 668 nm emitted by the discharge. Our measurements show a linear relationship between M and $\cal{P}$ for all accessible M values and for a wide range of experimental conditions (sample pressure, magnetic field, RF discharge level, etc.). This provides a second method of measurement of the 3He nuclear polarization which is simple to operate and is calibrated and is calibrated over a pressure range of 0.15 to 6.5 torr.

A frequency-stabilized LNA laser at $1.083~\mu$m : application to the manipulation of helium 4 atoms

We describe a single mode LNA ring laser, which emits 60 mW at 1.083 ~m. Thanks to a high frequency F-M- saturated absorption technique, this laser is directly locked to an atomic line in a ~He discharge cell. The residual frequency jitter is 130kHz. We then present two examples of laser manipulation of helium 4 atoms in the 2~Sj metastable state, using this laser a density increase of the atomic beam by a factor of 8, with one-dimensional optical molasses, and a selective deflection of the metastable helium beam using a laser beam with curved wavefronts.

A high power lamp-pumped LNA laser with thermally tuned etalon

This report describes arc-lamp pumped, tunable, continuous-wave LNA laser with improved output efficiency, suitable for optical pumping of helium. Using thermal tuning of intracavity etalons instead of angle tuning reduces losses caused by walk-off effects and provides continuous frequency scanning without a significant decrease in laser power. We obtain an output power of 4 W in a linewidth of 2.5 GHz with the laser wavelength tuned to the 1.083 μm absorption line of metastable helium. This result represents a fourfold gain in efficiency compared with conventional tuning by tilting. The laser provides efficient polarization of helium by optical pumping in various applications, such as nuclear spin polarization of 3He and spin-polarized electron sources.

Tunable diode-laser-pumped solid state LNA laser for helium spectroscopic experiments

We have designed, built, and tested a compact, integrated, single-mode solid state LNA laser pumped by a semiconductor laser array for exciting the He resonance line at lambda = 1.083 microm. The laser's three major components are mounted on a single aluminum base, and the diode laser and its beam shaping optics are mounted on a separate stage. This compact and stable structure provides good frequency stability and nearly pure TEM(00) transverse mode operation. The laser can be tuned around the metastable He resonance transition in a single longitudinal mode with linewidth congruent with 5 MHz using a solid, 60% coated intracavity 0.25-mm thick etalon. Saturated absorption signals on this transition have been used to measure the stability and tuning range. We have measured the properties for several crystals and calculated the expected performance characteristics to compare with the measured ones.

4He optical pumping with polarization modulated light

In optical pumping experiments using a laser, beam polarization can be changed easily with the help of an electro-optic device. High frequency modulation of a LNA laser beam polarization has been used to pump 4He (2 3S 1) metastable atoms. New resonances, never observed before, have been studied theoretically and experimentally, and application to high sensitivity magnetometers is suggested.

A HIGH POWER LNA LASER FOR APPLICATION TO A NEW POLARIZED ELECTRON SOURCE

The recent development of high energy electron accelerators has generated a renewed interest in high current, high polarization electron sources. We have investigated several modifications to a method based on a pumped helium afterglow from which we expect improvements over the performances. These ones include the development of a high power, tunable LNA laser and the application of a new optical pumping scheme to the metastable helium atoms.

4He optical pumping with intensity modulated laser light

4He (2 3S1) metastable atoms are optically pumped with intensity modulated light. The use of a single mode diode-pumped LNA laser as the pumping source, allows the study of resonance signals predicted by the optical pumping theory but not yet observed. Resonances are detected on the transmitted pumping beam at the modulation frequency and its harmonics. Application of this method to high sensitivity magnetometers is suggested.

Frequency-stabilized LNA laser for application in He(23S) optical pumping

A single-mode, standing-wave lanthanum neodymium magnesium hexaaluminate laser is described that is suitable for application in He(23S) optical pumping. The laser is frequency stabilized by reference to an external temperature-controlled Fabry–Perot étalon using simple control circuitry. Tests show that the laser can provide stable, efficient optical pumping of a collimated beam of He(23S) atoms resulting in polarizations approaching 100%.

Improved source of polarized electrons based on a flowing helium afterglow

The performance of the Rice source of spin polarized electrons, which is based on an optically pumped flowing helium afterglow, has been substantially improved. He(23S) metastable atoms contained in the afterglow are optically pumped using 1.08 μm 23S1↔23P1 radiation from an LNA laser. Spin conservation in subsequent chemi-ionization reactions with CO2 results in the production of free polarized electrons that are extracted from the afterglow. At low currents, ≲1 μA, polarizations of 80%–90% are achieved. This decreases to ∼75% at 10 μA and to ∼50% near 100 μA. The polarization can be simply reversed (P→−P). The energy spread in the extracted beam is &amp;lt;0.4 eV, and the beam emittance is &amp;lt;4 mrad cm−1 at 270 eV. This source is suitable for use in a wide variety of applications, and is particularly attractive for use with the new generation of high-duty factor electron accelerators that are currently being developed.

Direct laser measurement of the Lamb shift of 23S-2(3)P transitions in helium.

For the first time, Lamb shifts of the 2 $^{3}S_{1}$-2 $^{3}\mathrm{P}_{0}$,1,2 transitions in helium have been measured directly with an LNA laser. The absolute wavelengths have been measured to a precision of 1 part in ${10}^{8}$, or ${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The Lamb shifts have been determined to 6 parts in ${10}^{4}$. Our results agree well with previous, indirect measurements, but represent a fivefold improvement in precision. The experimental results are compared with recent precision calculations. The obtained experimental Lamb shifts are 1 order of magnitude more precise than current theory.

UN laser solide accordable pompe par diode

In early papers we described the first end diode pumped LNA (La x Nd 1− x MgAl 11O 19) laser. We report larger performances of the continuous emitted laser power and the very interesting new possibility of tuning the emitted wavelength from 1.046 μm to 1.090 μm without extinction and with a slope efficiency of about 25%.

Nd:LNA laser optical pumping of 4He: Application to space magnetometers

We have observed Hanle signals and n=0, p=1 parametric resonances of 23S1 metastable helium atoms in a discharge cell by optically pumping the helium atoms with a tunable Nd:LNA laser. These resonances were used to construct a sensitive magnetometer for the measurement of very small magnetic fields. Since magnetometer sensitivity is proportional to the slope of the parametric resonance signal (signal amplitude divided by linewidth), the slopes for single-line laser pumping were compared with similar quantities obtained from conventional helium lamp pumping. Laser pumping yielded 45 times greater slopes with comparable power requirements, thus establishing the potential for developing ultrasensitive resonance magnetometers using single-line laser pumping.

Diode pumping of LNA lasers for helium optical pumping

Neodymium-doped LNA laser crystals (La x Nd 1- x MgAl 11O 19) have been pumped by laser diode arrays emitting around 800 nm. With longitudinal pumping using two 200 mW diode arrays focussed on the crystal end, 10 mW of power was obtained at 1.054 μm. With the insertion of a Lyot filter and a thin etalon, tuning across the 1.082 μm band was possible. Tuning the LNA laser output to the resonance transition of helium-4 (2 3S 1-2 3P 1) at 1.083 μm enabled us to optically pump the metastable helium atoms in a discharge cell and record magnetic resonance signals. Transverse pumping of the LNA crystals by a high-power, quasi-cw array was also successfully demonstrated.