Tunable Laser Applications Research Articles

New Cr 4+ activated compounds in tetrahedral sites for tunable laser applications

The three new Cr 4+ doped matrices studied in this work exhibit only tetrahedrally coordinated lattice sites for the small cations and therefore will not incorporate Cr 3+ ions. The Cr 4+ doped compounds SrGa 4O 7 and Sr(Ga, Al) 2O 4 exhibit broad band IR fluorescence. But it appears difficult to combine easy crystal growth and good optical properties. If Cr 4+:SrGa 4O 7 can be grown by Czochralski method, its fluorescence lifetime is very short (1 μs at 100 K). On the contrary for Cr 4+:Sr(Ga, Al) 2O 4, the 100 K fluorescence lifetime can reach 35 μs (and 10 μs at 300 K), but the hexagonal-monoclinic structural transition prevents to grow good quality single crystals. Cr 4+:Li 2MgSiO 4 is a remarkable compound. At 300 K it exhibits broad and intensive fluorescence peaking at ∼ 1.2 μm. The fluorescence lifetime exceeds 100 μs at 300 K and 400 μs at ∼ 50 K. This is the highest value reported so far, to our knowledge, for a Cr 4+ activated material. The very long fluorescence lifetime and its temperature dependence are explained by the thermalization of the Cr 4+ 3T 2 and 1E levels, the 1E level being the lowest one. Crystal growth of Cr 4+:Li 2MgSO 4 using the flux method is in progress.

Application of tunable excimer lasers to combustion diagnostics: a review

Tunable excimer lasers are being used to produce species-, space-, and time-resolved images of complex gaseous media. These media may be analyzed for composition, density, temperature, or flow velocities. The techniques are, in general, highly selective, sensitive, and nonintrusive and are being made possible by recent technological developments in these UV lasers and in intensified cameras, imaging spectrographs, and fast digital image processing. We describe the needs for laser diagnostics in combustion, the physical mechanisms, the relevant spectroscopy, typical experimental setups, and equipment considerations. Precision and accuracy are discussed on the basis of some simple, but realistic, calculations intended to guide the experimentalist in design considerations and to reveal potential sources of errors in the often difficult conversion of raw data to values for such quantitative parameters as densities or temperatures. Finally we present an overview of previous results, select some examples that show the power of tunable excimer laser diagnostics in combustion, and present some suggestions for future directions.

Tunable Solid-state Laser. Application of Tunable Solid-State Lasers to Biophotonics Information Sensing.

Recent interest in biomedical imagings using lasers has been spurred by the need of nonionizing medical imaging diagnostics. Tunable solid-state lasers are well suited for spectroscopic measurements and imaging of biological tissues, which are expected to provide functional information of the samples. This paper summarizes our recent development of a laser-diode pumped, single-frequency CW Cr: LiSAF laser which has been demonstrated to be tunable over a wide range of 150 nm near the wavelength of 875 nm. By reviewing our recent progresss of optical imaging and computed tomography of tissues and tissue-like phantoms, we show some of the potential applications of the tunable solid-state lasers.

Long periodic superstructure Bragg gratings in opticalfibres

A 40 mm long optical fibre grating superstructure is written by translating an ultraviolet writing beam along a fibre and phase-mask assembly while its intensity is periodically varied. The grating reflects at multiple wavelengths, equally spaced by 0.13 nm, over a range of more than 1.0 nm. This grating structure has applications in signal processing and tunable fibre lasers.< >

Agile solid state dye lasers

Different organic dye molecules were incorporated in solid gels by the sol gel process with a view to develop tunable solid state laser applications. We studied the laser efficiency of these materials by using a nanosecond frequency doubled Nd:YAG as the pump laser. Slope efficiency up to 30% with 3 mJ output energy and half energy lifetime of 40,000 shots were thus obtained. This large lifetime was observed with the perylene red molecules despite of a lower slope efficiency (19%). Tunability over 50 nm was obtained with the perylene or pyrromethene dyes and 75 nm in the case of the xanthylium dye

Tunable diode-laser measurement of carbon monoxide concentration and temperature in a laminar methane–air diffusion flame

The application of tunable diode lasers for in situ diagnostics in laminar hydrocarbon diffusion flames is demonstrated. By the use of both direct-absorption and wavelength-modulation (second-derivative) techniques, carbon monoxide concentrations and the local flame temperature are determined for a laminar methane-air diffusion flame supported on a Wolfhard-Parker slot burner. In both cases the results are found to be in excellent agreement with prior measurements of these quantities using bothrobe and optical techniques.

Mode competition and switching in three section DBR tunable lasers

Mode competition in three section DBR tunable lasers is studied with a simple Fabry-Perot like description. The problem is analysed from the point of view of tunable laser applications in multicarrier communication systems. The maximum power for single mode operation and the switching between adjacent modes are discussed.

“Fluorescence properties of Cr3+ in natural eosphorite crystals”

The fluorescence properties (excitation, emission and lifetime) of Cr3+ ions in natural Eosphorite crystals (AIPO4 (Mn,Fe) (OH)22H2O) have been systematically investigated in the temperature range 10 – 300 K. This ion shows the two emissions 2E → 4A2 and 4A2 → 4A2 typical of an intermediate crystal field material giving a spectroscopic parameters very similar to those reported for Alexandrite what makes this host a possible candidate for tunable laser applications.

Laser-excited luminescence in Ti-doped MgAl2O4 spinel

The photoluminescence (excitation, emission, and fluorescence decay time) spectra of spinel (Ti:MgAl2O4) excited by pulsed Nd:YAG and dye lasers have been systematically investigated. Excitation into the T2g→Eg crystal-field transition of Ti3+ produces a broad infrared emission band at 805 nm which could, in principle, be used for tunable laser applications. Two different Ti3+ centers with lifetimes of 4.2 and 41 μs contribute to this emission. At the same time this IR band can also be observed under high-intensity excitation in the ultraviolet region (266 nm) via a two-photon process.

Spectroscopy and applications of molecules in glasses

A variety of organic colorant species, showing strong absorption bands in the visible and high-yield broad-band luminescence can be incorporated at ambient temperature in the homogeneous precursor solution of sol-gel glasses which then vitrifies by moderate heating. The spectroscopic properties of such doped sol-gel glasses are reviewed, and their applications in tunable dye lasers, materials for non-linear optics, luminescent solar concentrators, and other devices are outlined.

Luminescence of Ce 3+-doped aluminoborates, M 3Al 6B 8O 24 (M = Mg, Ca, Sr, Ba)

Newer dielectric materials doped with appropriate impurities are often sought for tunable blue laser applications. Thus, the luminescence properties of Ce 3+ in the novel ternary borates, M 3Al 6B 8O 24 (M = Mg, Ca, Sr, Ba) have been investigated. The single excitation band centred around 310 nm and the broad emission band maximising around 400 nm are devoid of the characteristic Ce 3+ doublet and the vibrational fine structures, even at low temperatures. These luminescence features are due to the extensive crystal-field splitting of the 4f ground state. The large Stokes shift of ∼7000 cm −1 and the half-band-widths are influenced by M 2+ ions.

Flashlamp-pumped high-energy dye lasers.

Powerful and tunable lasers in the visible region are expected to be realized in the very near future, for the purpose of laser isotope separation and applications of tunable dye lasers, not only in our country but also in the United States and Europe. However, it is not so easy to realize both high power or energy and good tunability.In this paper, we wish to report an investigation of verious types of high-power tunable dye lasers which can be used as a pumping source for atomic uranium isotope enrichment, and high power techniques of dye laser apparatus, especially flashlamp-pumped high energy dye lasers developed in our laboratory.

Tunable lasers. Application to laser isotope separation. Selective photochemical reaction by tunable lasers.

General aspects and recent progress of laser isotope separation are introduced. From the veiwpoint of tunable laser application, emphasis is placed on the spectroscopic characteristics of isotope-selective photochemical reactions for both atomic (AVLIS) and molecular (MLIS) processes with examples of U, Pd, CHF3, and UF6. Potentials of newly developed lasers such as Ti: Al2O3 and FEL are also discussed.

Laser spectroscopy of desorbing molecules

In this article the application of tunable dye lasers to desorption phenomena is illuminated. These lasers provide radiation continuously tunable from 105 nm in the vacuum ultraviolet to about 10 μm in the mid-IR. By employing either laser induced fluorescence (LIF) or resonance enhanced multiphoton ionization (REMPI) spectroscopy almost all diatomic and many polyatomic molecules can be probed with the sensitivity required to detect desorbing molecules under UHV conditions. The spectral resolution of the lasers is sufficiently high that rotational state selectivity is achieved. Recent developments permit in addition the velocity distributions of molecules to be determined with internal quantum state resolution. Therefore very detailed information about the molecular dynamics has been obtained. In most experiments so far reactive recombinations off surfaces have been investigated. In this paper special emphasis will be given to the recombination of hydrogen on copper and palladium surfaces. For these systems very detailed data about the internal state populations at various surface temperatures have been obtained. The rotational cooling previously observed in molecular beam scattering has also been established for desorption. Strong vibrational excitation has been observed, which in the case of desorption from copper may be associated with the recombination dynamics, whereas for desorption of D2 from Pd(100) a molecular precursor state might be responsible. By measuring the velocity distribution in each quantum state, the complete energetics of the desorbing molecules has been determined. Some first experiments on laser induced desorption with state selective detection of the desorbing molecules will also be discussed. Finally, making use of the polarization analysis of the signal, alignment effects in the desorption can be observed, permitting observation of molecular dynamics with a “magnifying glass”.

Electron-spin resonance and fluorescence investigation of LaMgAl11O19:Ti3+, a potential tunable laser material

Single crystals of LaMgAl11O19:Ti (LMA:Ti) have been grown from the melt by the Verneuil (flame fusion) process. As-grown crystals contain titanium in both 3+ and 4+ oxidation states. Ti4+ ions can be reduced into the 3+ state by annealing at 1200 °C under hydrogen atmosphere. The crystals exhibit a broadband fluorescence extending from ∼600 to 1200 nm and peaking around 775 nm. The fluorescence lifetime is found to be ∼6 μs at 10 K against ∼4 μs at 300 K; it does not depend significantly on the emission wavelength, this indicating that fluorescence originates mainly from one type of Ti3+ active ions. Electron-spin-resonance (ESR) investigations reveal that Ti3+ ions are distributed among the three octahedral sites of the magnetoplumbite structure of the host, with a marked predominance for the regular octahedral site (2a), which contains about 90% of the titanium detected by ESR. Crystal field splitting of the t2g level has been estimated for the three sites and it is proposed that Ti3+ in the (12k) site is adjacent to a cationic defect. This new material is of potential interest for near infrared tunable laser application.

Laser atomic absorption spectroscopy applying semiconductor diode lasers

The application of tunable single mode semiconductor diode lasers in atomic absorption spectroscopy is discussed in general. The use of several diode lasers, periodical modulation of the laser powers and Fourier analysis of the absorption signals allow background-corrected multi-element atomic absorption spectroscopy with extended dynamic range and internal standardization. This is demonstrated by the simultaneous determination of rubidium and barium in aqueous solutions with a commercial graphite tube atomizer.

Optical properties of β-Ga 2O 3:Cr 3+ single crystals for tunable laser applications

Single crystals of β-Ga 2O 3:Cr 3+ with various doping levels have been grown by the floating zone technique. In this material, the room temperature fluorescence is dominated by the broad band 4T 2→ 4A 2 emission extending between 650 and 950 nm, with a 210 μs lifetime. At 77 K, the 4T 2 level is depopulated so that fluorescence originates only from the 2E level with a 2.3 ms lifetime. The temperature dependence of the lifetime indicates that the 4T 2 level lies approximately 600 cm -1 above the 2E level. These characteristics are similar to those of alexandrite: Cr 3+. Therefore, β-Ga 2O 3:Cr 3+ may be an interesting new material for tunable laser applications.

Rotational spectroscopy of molecular ions using diode lasers

We report here the first application of tunable diode lasers to study the pure rotational spectroscopy of molecular ions. High J rotational transitions of molecular cations ArH+, NeH+, HeH+, OH+, H2O+, and anion OH− have been observed.

Broad band fluorescence of transition metal doped garnets and tungstates

We give a survey on the laser relevant spectroscopic properties of Cr 3+ and Mn doped garnets and tungstates. From absorption, fluorescence, excitation and lifetime measurements between 4K and 300K the energy level schemes of the active ions are derived. It is shown, that Cr 3+ exhibits broad band fluorescence in crystals with rather low crystal field and/or low site symmetry. This is demonstrated by the different garnets, by the tungstates Al 2(WO 4) 3 and Sc 2(WO 4) 3 and by Cr: ZnWO 4. In the latter compound the maximum of the fluorescence is shifted to about 1μm due to the acentric Cr 3+ site. Mn is incorporated in YAG as Mn 2+, Mn 3+ or Mn 4+ depending on the growth conditions. From the spectroscopic data Mn 3+ is found to be a promising ion for short wavelength tunable laser applications.

Laser spectroscopy: 7. Multiphoton and multistep methods

Multiphoton and multistep spectroscopy of atoms and molecules is a rapidly developing branch of laser spectroscopy which relies almost exclusively on the application of tunable lasers. This article reviews the different techniques which have been developed.