Room-temperature Cr Research Articles

Femtosecond Cr2+-Based Lasers

We review a novel class of femtosecond Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -doped ZnSe and ZnS lasers, which operates in a very important for applications wavelength range between 2 and 3.5 μm and which generates ultrashort optical pulses that are only five optical cycles in duration. Room-temperature Cr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> -lasers provide tens of Watts average power, >70% slope efficiency, ultrabroad tunability (~1400 nm between 2 and 3.4 μm) in the continuous wave regime and GW-level peak powers in the amplified femtosecond regime. Different mode-locking techniques from Kerr-lens to graphene saturable absorbers have been demonstrated, and dispersion compensation methods from bulk materials to chirped mirrors allowed the realization of self-starting few-optical cycle oscillators and the demonstration of a number of applications in spectroscopy and nonlinear optics. The Watt level few-optical cycle Cr:ZnS oscillator <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> operating at 2.4 μm is distinguished by extremely short pulse duration of only 41 fs, hundreds of kilowatt peak powers, and tens of nanojoule pulse energies. Using the direct diode-pumping or fiber laser pump sources such a laser can be made reliable and compact, which paves the way to industrial realisation and applications in environmental analysis, oil and gas sensing, hazardous gas detection, breath analysis, fine material processing of semiconductors, composite materials, and glasses.

Broadly tunable continuous-wave diode-pumped Cr4+:YAG laser

Abstract We describe a widely tunable, continuous-wave, room temperature Cr 4+ :YAG laser with direct pumping by two high brightness 4 W InGaAs laser diodes. In a tunable configuration, the output wavelength covered a span of 197 nm (1356–1553 nm) and provided a maximum power of 195 mW. A maximum non-tunable output power of 260 mW was obtained with a 0.6% transmission output coupler (OC) and 6.6 W of incident pump power. Pumping at two different wavelengths, 911 and 968 nm, was investigated.

Broadly tunable compact continuous-wave Cr^2+:ZnS laser

We report the development of a continuous-wave, room-temperature Cr(2+) ZnS laser that is compact and tunable over 700 nm. The laser is pumped by a diode-pumped Er-fiber laser and generates 0.7 W of linearly polarized radiation at 2.35microm , at up to 40% slope efficiency. Cr(2+) ZnS directly diode-pumped at 1.6microm yields polarized radiation that is tunable over 400 nm at up to 25 mW of output power. A comparison of Cr(2+) ZnS with Cr ZnSe (70 mW, 350 nm) in a similar setup is given. As opposed to Cr ZnSe, the Cr ZnS laser is intrinsically polarized. Finally, we observe sensitization of the output radiation by a few milliwatts of the visible (470-500-nm) and near-infrared (740-770-nm) radiation.

Optimization of power performance in room-temperature continuous-wave Cr 4+:YAG lasers

Experimental and numerical studies were carried out to investigate the power performance and the role of thermal loading in room-temperature Cr 4+:YAG lasers. The numerical model accounts for thermal loading effects due to the temperature dependence of the fluorescence lifetime. Experimental pump absorption, laser threshold, and laser efficiency data were first analyzed to determine the absorption, emission, and excited-state absorption cross-sections. Best-fit cross-section values were then used to perform numerical optimization studies. Results showed that a 2-cm-long crystal with a total unsaturated pump absorption of 64% at 1064 nm, should produce the maximum output power from the laser. Furthermore, the optimum output coupling of the resonator was determined to be 1.7%.

Threshold optimization of all-solid-state Cr:forsterite lasers

The pumping threshold of a Cr:forsterite laser is lowered by optimizing a double-pass pumping in a sufficiently short crystal. This solution for the first time allows nearly room-temperature Cr:forsterite cw operation with a threshold as low as 330-mW at 1064 nm and permits the laser to be pumped with a single transverse mode vanadate minilaser delivering only 900 mW.

Optimum crystal parameters for room-temperature Cr 4+:forsterite lasers: experiment and theory

Room-temperature Cr 4+:forsterite lasers experience deterioration in continuous-wave power performance due to thermal loading caused by the temperature-dependent fluorescence lifetime and the low heat conductivity of the host. The study presented in this paper uses a numerical model to analyze the experimental threshold and efficiency data of Cr 4+:forsterite lasers by accounting for pump-induced thermal gradients, the temperature dependence of the fluorescence lifetime, absorption saturation at the pump wavelength, and excited-state absorption at the lasing wavelength. Very good agreement was obtained between theoretically predicted trends and the experimental data. The best-fit values of the stimulated emission cross-section and the excited-state absorption cross-section were determined to be 1.16×10 −19 cm 2 and 0.18×10 −19 cm 2, respectively. Optimization studies further predict that at an incident pump power of 8 W, a 2-cm-long Cr 4+:forsterite crystal with a differential absorption coefficient of 0.31 cm −1 should produce the highest continuous-wave output around room temperature.

Directly diode-pumped tunable continuous-wave room-temperature Cr^4+:YAG laser

We report what is to our knowledge the first directly diode-pumped tunable (over 120 nm) continuous-wave Cr(4+): YAG laser, operating near 1.5 microm . At room temperature the laser delivered as much as 200 mW of power at 4 W of absorbed pump power. We also report observation of slow laser output degradation and bleaching in highly concentrated crystals, which we suggest is due to a photorefractive phenomenon.

Efficient, kHz repetition rate, gain-switched Cr:forsterite laser

We have developed a gain-switched room-temperature Cr:forsterite laser operating at repetition rates of between 1 and 34 kHz, and pumped by a continuous wave, Q-switched Nd:YAG laser. With optimised output coupling, an output pulse energy of 52 μJ was measured at 1.5 kHz repetition rate, corresponding to 11% efficiency and 13% slope efficiency. Threshold pulse energy was 53 μJ. Output power of 370 mW was obtained at 10 kHz repetition rate and 4.4 W pump power. Water cooling was not required for repetition rates up to 10 kHz. In a tunable, folded resonator, the Cr:forsterite wavelength tuned between 1173 and 1338 nm. This laser operated with maximum pulse energy of 34 μJ, efficiency of 13%, and power of 307 mW. The laser output was close to diffraction-limited with M2 of 1.2.

Corrections to "Experimental and numerical investigation of thermal effects in end-pumped Cr4+:forsterite lasers near room temperature"

In the above-named article, which investigated the effects of thermal loading in room-temperature Cr4+:forsterite lasers, a scaling error was made in the best-fit and optimization calculations. In the comparison of theory with experiment (Fig. 8), the correct best-fit balue of the stimulated emission cross section should have been 0.98 x 10-19cm2. In addition, the correct optimum value of the small-signal absorption coefficient, which minimizes the incident threshold pump power (see Fig. 10), should be 0.34 cm-1, corresponding to a total unsaturated pump absorption of 49% for a 2-cm-long crystal. The theoretically predicted trends were not affected by the corrections.

Cr 4+ -doped tunable solid-state lasers in the near infrared

The spectroscopic characteristics, different modes of operation, and applications of the recently developed Cr4+-doped laser systems which operate in the near-infrared wavelength regime are discussed. In particular, a detailed account is given of the developments that have taken place in system optimization and ultrashort optical pulse generation in Cr4+:forsterite and Cr4+:YAG lasers producing coherent light outputs around 1.3 and 1.5 e m, respectively. Thermal loading which has limited the production of high-output powers in Cr4 +:forsterite is further addressed and the results of a recent experimental study aimed at minimizing thermal loading in room-temperature Cr4 +:forsterite lasers are presented. In these experiments, a Nd:YAG-pumped Cr4 +:forsterite crystal with a differential absorption coefficient of 0.57 cm−1, produced as high as 900 mW of output power at 15°Cin a resonator with an output coupler of 4.7% transmission. To the author’s knowledge, this represents the highest power performance reported to date from a room-temperature Cr4 +:forsterite laser and increases the prospects of obtaining high, continuous-wave output powers from these systems.

Determination of the optimum absorption coefficient in Cr^4+:forsterite lasers under thermal loading

We present the results of a novel experimental and numerical investigation aimed at minimizing thermal loading effects in room-temperature Cr(4+): forsterite lasers. In the model we numerically calculated the incident pump power required for oscillation threshold to be attained by taking into account pump absorption saturation, pump-induced thermal gradients inside the crystal, and the temperature dependence of the upper-state fluorescence lifetime. Excellent agreement was obtained between model predictions and experimental threshold data. We then used the model to calculate the optimum absorption coefficient that minimizes the incident threshold pump power. At a crystal boundary temperature of 15 degrees C the optimum value of the absorption coefficient was numerically determined to be 0.64 cm(-1) . Such optimization studies, which are readily applicable to other laser systems, should make a significant contribution to the improvement of the power performance of Cr(4+): forsterite lasers at room temperature.

Thin crystal, room-temperature Cr^4+:forsterite laser using near-infrared pumping

We describe a new design for chromium-doped forsterite lasers based on near-IR (700-800-nm) pumping of a thin (3-mm) crystal. In contrast with pumping at 1.06 microm, near-IR pumping permits the use of shorter crystal lengths, which enable one to develop compact and diode-pumped laser geometries. Near-IR pumping also results in an increased effective figure of merit and tuning performance. Using a Ti:Al(2)O(3) pump laser, we investigated cw laser characteristics over a range of pump wavelengths compatible with diode pumping. Room-temperature cw operation with a tuning range of 1175 to 1375 nm was achieved. Kerr-lens mode-locked operation of this laser was also demonstrated with pulse durations of ~50 fs.

FORMATION OF INTERFACES AND TEMPLATES IN THE Si(111)-Cr SYSTEM

The literature data and new data on investigation of the Si(111)-Cr system were systematized to the diagram of structural phase transitions. The ranges on this diagram give the formation conditions of various phases and reflect the mechanism of the Cr/Si (111) and CrSi 2/ Si (111) interface formation during room-temperature Cr deposition following annealing. The proofs of the multilayer surface phase formation and the data about transitions between the multilayer surface phases and bulk silicides during formation of the Cr/Si (111) and CrSi 2/ Si (111) interfaces were presented. The investigation of A- and B-type CrSi 2 templates formation was carried out. It was discovered that nucleation conditions and, in particular, the type of surface phases determine the azimuthal orientation of the epitaxial CrSi 2 islands relative to Si (111) under their nucleation. The A- and B-type CrSi 2 epitaxial films were grown by means of the template technique. The A-type CrSi 2 semiconductor film with low concentration and high mobility of holes was obtained.

Tunable room-temperature laser action of Cr4+-doped Y3ScxAl5?xO12

A new class of tunable room-temperature Cr4+ lasers is presented: Cr4+-doped Y3ScxAl5−xO12 garnets. With increasing scandium content the emission shifts to longer wavelengths due to the weakening of the crystal field. Free running laser wavelengths are 1440, 1498, 1548 and 1584 nm for x = 0, 0.5, 1.0 and 1.5, respectively. Continuous tunability is obtained from 1309 to 1628 nm.

Continuous-wave mode-locked Cr^4+:YAG laser

A cw room-temperature Cr(4+):YAG laser, tuning from 1.37 to 1.51 microm, is described. Mode locking of this novel laser is reported for what is to our knowledge the first time.

The reactive Cr/InP and Mn/InP interfaces

Soft x-ray photoemission spectroscopy studies were performed in ultrahigh vacuum on cleaved n-InP(110) with sequential room-temperature Cr and Mn depositions of up to 30 Å. The In 4d, P 2p, and Cr 3p or Mn 3p core levels were monitored as a function of coverage. Both systems exhibited strong metallic In-phase separation and surface segregation, formation of a metallic phosphide, and no evidence of island formation. Fermi level-pinning positions of 0.6 and 0.3 V below the CBM were estimated for the Cr and Mn systems, respectively, by deconvoluting the substrate from the interfacial components of the In core lines. These results are discussed in the context of different models of Schottky barrier formation.