Low Pump Threshold Research Articles

Continuous laser emission from sodium atoms by collision assisted two-step excitation

Continuous laser oscillation on different lines in the spectral range of 1.85 to 3.41 μm, corresponding to transitions between higher lying atomic sodium levels, has been obtained by optical excitation of sodium vapor with Rhodamine 6G dye-laser radiation, tuned either around the 3p−4d resonance (∼ 568 nm) or the 3p−5s resonance (∼ 615 nm). The pump mechanism consists of an atomic two-step excitation as well as an excitation of diatomic sodium molecules and subsequent molecular-atomic collisional energy transfer. Laser operation with low threshold pump power (<10 mW) and large pump laser detuning (500 GHz) has been observed.

Laser beam power fade induced by system and atmospheric effects

This manuscript provides a comprehensive review of the characteristics of Cr4+-doped solid-state lasers which produce broadly tunable coherent radiation in the near-infrared region of the electromagnetic spectrum between 1.13 and 1.63 μm. Cr4+-doped gain media have several favorable characteristics including broad absorption bands that overlap with the operating wavelengths of several commercial pump lasers, a 4-level energy structure that allows continuous-wave as well as pulsed operation with low threshold pump powers, and the presence of broad amplification bands for the generation of ultrashort optical pulses. In addition, non-linear frequency conversion schemes can be readily employed to construct broadly tunable coherent visible sources based on Cr4+-doped gain media. These favorable features make Cr4+-doped lasers potentially important in many applications in optical communications, eye-safe imaging, medicine, and spectroscopy.After a description of the basic physical mechanisms that lead to broad emission in tunable solid-state lasers in general and Cr4+-doped gain media in particular, the manuscript provides a detailed description of the operational characteristics of Cr4+-doped lasers, including rate-equation analysis of power performance, role of thermal effects, and different mode-locking techniques for the generation of ultrashort optical pulses. Later sections focus on the work performed in the development and characterization of specific examples of Cr4+-doped lasers. Particular attention is given to Cr4+:forsterite and Cr4+:YAG laser systems due to their superior power performance. Gain-switched, continuous-wave, and mode-locked operations of these lasers are described with a particular emphasis on recent developments. Studies carried out with other Cr4+-doped lasers such as Cr4+:Y2SiO5, Cr4+-doped oxyapatite, Cr4+-doped garnets, and Cr4+:Ca2GeO4 are also described. Finally, use of non-linear conversion schemes in the generation of visible radiation with Cr4+-doped lasers is discussed. In particular, experiments that have been performed with pulsed and continuous-wave Cr4+:forsterite lasers to generate broadly tunable radiation in the 565–685 nm range of the electromagnetic spectrum are reviewed.

Optically pumped cw molecular bismuth laser

Continuous laser oscillation of diatomic bismuth molecules was observed. The gaseous Bi2 was optically pumped on individual vibrational-rotational lines of the A–X band system by several single mode lines of a stabilized Ar+ laser. More than 150 Bi2 laser transitions are observed in the wavelength range between 590 and 790 nm and assigned to the A–X system. Laser power conversion efficiencies of up to 15% for broadband laser emission and up to 2.5% for single frequency laser emission were observed. Maximum Bi2 laser power was 150 and 25 mW, respectively. Low pump thresholds of the order of 40 mW are observed for single mode pumping of the strongest lasing transitions. Gain was determined from maximum output coupling to g≊0.02 cm−1. Using the optically pumped cw Bi2 laser as its own probe we measure the hyperfine structure of the Bi2(A–X) v′ = 17−v\ = 40 P(256) transition.

Optically pumped continuous wave submillimeter emissions from H 13COOH: Measurements and assignments

Twenty-one emissions were obtained from the H 13COOH laser optically pumped by a CO 2 laser. Some of them are very powerful and are observed with a low-threshold pumping. They increase the number of strong lines available with submillimeter lasers. A study of the emission spectrum based on the results obtained from the assignment of the 12C isotopic species allowed us to assign most of the observed emissions, and a set of parameters for the ν 6 excited state of this molecule is derived from this study. The results obtained were checked by RF spectroscopy inside the cavity of a CO 2 laser.

Phosphate and borate crystals for high optical gain

We report on crystal growth, spectroscopic and laser properties of stoichiometric rare earth phosphate and borate laser crystals such as NdP 5O 14, NdLiP 4O 12, and NdAl 3(BO 3) 4. The lasers can be operated at 1.06 and 1.3 μm wavelength and exhibit high gains (⩽ 1.7 per optical wavelength) and low pump thresholds (< mW). The borates combine high optical gain, nonlinear optical properties and Cr 3+ activation. We describe the crystal structure of the borates (C2 and C2/c polymorphy) and its connection to nonlinear properties (acentric C2 space group) as well as spectroscopic properties (three different Nd 3+ sites).

Laser action in para-quaterphenyl vapor pumped by XeCI* laser radiation

A new approach is proposed to the search for active media involving a theoretical study of the spectral, luminescence, and lasing properties of organic molecules. Laser action was obtained in gas-phase paraquaterphenyl (λ1=361.5 nm) with a low threshold pumping level (1.1 MW/cm2). The lasing capacity of some substituted forms of para-quaterphenyl is predicted.

New 17–21-μm laser lines in C_2D_2 using a continuously tunable CO_2 laser pump

The generation of new 17–21-μm laser lines in C2D2 (dideuteroacetylene) by using a continuously tunable CO2 laser pump is reported. Several of the transitions have been found to exhibit a low pump threshold and high efficiency.

The growth of laser quality NdP 5O 14 crystals

Neodymium pentaphosphate, NdP 5O 14, is the first successful result of a new approach in the synthesis of laser materials. Instead of doping the active ions as impurities into host materials, the actice ions are allowed to form specific stoichiometric compounds of their own. NdP 5O 14 is such a compound. It combines five desirable properties: high chemical and mechanical stability, low pump threshold, high optical gain, and small volume. We describe the growth of single crystals from polyphosphoric acid solution, and give initial results on ‘crystal engineering’ studies which yield decisive improvements of quality and laser properties of the crystals.

Resonantly pumped tunable stimulated recombination radiation in InSb

Magnetic-field tunable stimulated recombination radiation was observed in InSb at 20°K. By pumping resonantly with 5.1 μm (1955 cm -1) radiation, i.e. hω p ⪆ E g, we observed considerable lower threshold pump power densities compared to those obtained with other excitation mechanisms. The observed tuning range is about 45 cm -1 for fields up to 45 kG.

Luminescence from ionized F-aggregate centers in alkali halide crystals

Color centers in alkali halide crystals can be applied as high-gain active materials in tunable solid state lasers. When cryogenically cooled and optically pumped, these laser crystals have low threshold pump powers, relatively high output powers, and are smoothly tunable over a large fraction of their broad emission bands. Using various color center types and host lattices, the combined tuning range of color center lasers covers presently the near-infrared region from about 0.8 to 4 μm. In single-mode cw operation color center lasers have extremely narrow spectral line-widths; in mode-locked operation they can provide pulses with ultranarrow temporal widths. These properties make them very attractive for spectroscopic studies requiring high spectral or temporal resolution. This paper reviews the optical properties of the main laser-active color center types, the techniques used for their production, and their laser characteristics. Furthermore, a brief summary is given on the application of color center lasers.