Laser emission spectra

Fig. 16 Laser emission spectra from the polymer-stabilized blue phase of the (110) crystal [44]...

Chemical-laser emission spectra up to 1967 have been compiled by Patel 6 ). There is some inconsistency between HF laser spectra obtained in different laboratories and with different experimental set-ups. This is probably due in part to the absorption of several HF lines by the atmosphere inside or outside the laser cavity. However, there is additional inconsistency between the emission spectra of infrared chemiluminescence experiments and HF chemical lasers. While spontaneous luminescence predicts a peak in the v=2 - 1 transitions around /=614>, the laser emission usually... 

Figure 11.16 Space distribution of the laser emissions. The excitation beam width was 20 fim. (a) The red points show the unusually narrowed emission and other colors are photoluminescence or ordinary ASE. (b) The space-distributed laser emission spectra relative to the zero position arbitrarily chosen. Reprinted with permission from K. Shimizu, Y. Mori and S. Hotta, Laser oscillation from hexagonal crystals of a thiophene/phenylene co-oligomer, J. Appl. Phys., 99(6), 063505 (2006). Copyright 2006, American Institute of Physics...

Examples of the laser emission spectra just above the lasing threshold are presented for two laser structures the first with 5-nm QWs and the second with 2-nm QWs. The emissions from both of our samples are TE polarized, which strongly confirms that stimulated emissions have been obtained. Such stimulated emissions for the thinner QWs shift toward higher energies for 53 meV. If we take into account the flat band model and perform calculations for inter-sub-band transitions, this difference should be 48 meV in cases of 5-nm and 2-nm QWs, which corresponds well with our experimental results. This also proves that the laser emissions in our samples take place in the active region of the laser structure, and not, for example, in the substrate. 

Figure 3.29 Room-temperature laser emission spectra. Inset shows clearly resolved modes. (After Ref. [150].).

Fig. 6. Laser emission spectrum from DCM/dendrimer solution in cuvette. Inset schematically illustrates experimental setup...

Sensitivity can be improved by factors of 10 using intracavity absorption, placing an absorber inside a laser resonator cavity and detecting dips in the laser emission spectrum. The enhancement results from both the increased effective path length, and selective quenching of laser modes that suffer losses by being in resonance with an absorption feature. 

Figure 10.28. Reflection spectrum (1), fluorescent emission spectrum (2) by excitation at 532 nm, and laser emission spectrum (3) by excitation with a second harmonic iight of Nd-YAG laser of a Ch mixture of E44, S811, m-azo-8, and DCM (73.1/22.2/4.3/0.4 in wt%). Source Kurihara et al., 2006.

FIGURE 22.42 Random laser emission spectrum of a DOO-PPV in toluene solution that is infiltrated into an opal photonic crystal. The inset shows the opal, which is composed of silica spheres in an FCC lattice and the laser excitation and collection geometries. (From Poison, R.C., Chipouline, A., and Vardeny, Z.V., Adv. Mater., 13, 760, 2001. With permission.)... 

The laser emission spectrum is shown in Figure 11.13. A progression of extremely narrow emission lines clearly appears around 689 nm. The FWHM of the individual lines is limited to 38 pm (close to the apparatus resolution limit). These narrow lines arise regularly at an interval of 121 pm. Figure 11.14 shows the photopump intensity dependence of the peak intensities of the emission spectra. A threshold is clearly noted at 750 p,J cm". Concomitantly, the spectroscopic profiles dramatically change below... 

Fig. 38. Laser emission spectrum near 2.7 pm for a bulk glass at various pumping levels (Auzel et al. 1988b).

Figure 13-21. (a) Schematic illustration of a dye-infiltrated opalphotonic crystal usedfor measuring lasing action in the [111] direction, (b) the [111] laser emission spectrum (solid curve) and optical density spectrum for an Oxazine 725 dye-infiltrated opal, and (c) the laser emission spectrum (solid curve) and optical density spectrum (dotted curve) for a [2 2 0] Stilbene 420 dye-infiltrated opal (Shkunov, 2002). 

Figure 10-8. Emission spectra of a free standing film of a blend system consisting of 0.9% MEH-PPV in polystyrene with ca. I011 cm 3 TiOj-particlcs. The nanoparlicles act as optical scattering centers. The emission spectrum is depicted for two different excitation pulse energies. Optical excitation was accomplished with laser pulses of duration I Ons and wavelength 532 nm (according to Ref. 171).

Chou P, McMorrow D, Aartsma TJ et al (1984) The proton-transfer laser. Gain spectrum and amplification of spontaneous emission of 3-hydroxyflavone. J Phys Chem 88 4596 1599... 

Fluorescein is excited at 494 nm, which fits to the argon-ion laser line at 488 nm, a very convenient feature for many microscopy experiments. It emits at 520 nm and the emission band is far from being sharp. The broad fluorescence emission spectrum varies with pH [18]. The advantageous photochemical properties of fluorescein are its high absorption (emax = 79,000M-1cm-1) and quantum... 

The fluorescent components are denoted by I (intensity) followed by a capitalized subscript (D, A or s, for respectively Donors, Acceptors, or Donor/ Acceptor FRET pairs) to indicate the particular population of molecules responsible for emission of/and a lower-case superscript (d or, s) that indicates the detection channel (or filter cube). For example, / denotes the intensity of the donors as detected in the donor channel and reads as Intensity of donors in the donor channel, etc. Similarly, properties of molecules (number of molecules, N quantum yield, Q) are specified with capitalized subscript and properties of channels (laser intensity, gain, g) are specified with lowercase superscript. Factors that depend on both molecular species and on detection channel (excitation efficiency, s fraction of the emission spectrum detected in a channel, F) are indexed with both. Note that for all factorized symbols it is assumed that we work in the linear (excitation-fluorescence) regime with negligible donor or acceptor saturation or triplet states. In case such conditions are not met, the FRET estimation will not be correct. See Chap. 12 (FRET calculator) for more details. 

As mentioned above, spectral imaging microscopy is a form of multidimensional fluorescent microscopy where a fluorescent emission spectrum is acquired at each coordinate location in the sample. This mode of imaging has been implemented for wide field, confocal, and two-photon laser scanning microscopy, and several excellent... 

The spectral resolution of the most monochromatic laser yet devised, expressed as frequency of the laser emission divided by the laser linewidth, is approximately 5 x 10. The laser in question is a special-purpose He-Ne laser with a nominal wavelength of 632.8 nm (15,308 cm l or 4.74 x 10 Hz in frequency units) and a linewidth of 7 to 10 Hz. It is difficult to grasp the physical significance of this degree of resolution. One illustration is that, if the spectrum of this laser were displayed on chart paper such that the zero of electromagnetic energy were located at the sun and 15,308 cm l were located at the orbit of Earth, the width of the peak representing the output of the laser would be 3 millimeters. 

A crystal activated with Ti + ions presents an absorption that peaks at 514 nm and the corresponding emission spectrum peaks at 600 nm. A sample of this crystal, which has an optical density of 0.6 at the absorption peak, is illuminated with an Ar laser emitting at 514 nm with a power of 2 mW. (a) Determine the laser power of the beam after it passes through the crystal, (b) If the quantum efficiency isrj = 0.6, determine the intensity (in photons per second) emitted as luminescence and the power dissipated as heat in the crystal. 

A host material is activated with a certain concentration of Ti + ions. The Huang-Rhys parameter for the absorption band of these ions is 5 = 3 and the electronic levels couple with phonons of 150 cm . (a) If the zero-phonon line is at 522 nm, display the 0 K absorption spectrum (optical density versus wavelength) for a sample with an optical density of 0.3 at this wavelength, (b) If this sample is illuminated with the 514 nm line of a 1 mW Ar+ CW laser, estimate the laser power after the beam has crossed the sample, (c) Determine the peak wavelength of the 0 K emission spectrum, (d) If the quantum efficiency is 0.8, determine the power emitted as spontaneons emission. 

Yttrium aluminum borate, YAlj (603)4 (abbreviated to YAB), is a nonlinear crystal that is very attractive for laser applications when doped with rare earth ions (Jaque et al, 2003). Figure 7.9 shows the low-temperature emission spectrum of Sm + ions in this crystal. The use of the Dieke diagram (see Figure 6.1) allows to assign this spectrum to the " Gs/2 Hg/2 transitions. The polarization character of these emission bands, which can be clearly appreciated in Figure 7.9, is related to the D3 local symmetry of the Y + lattice ions, in which the Sm + ions are incorporated. The purpose of this example is to use group theory in order to determine the Stark energy-level structure responsible for this spectrum. 

Figure 12. Typical procedure to measure the sample temperature in a laser heating experiment. The experimental emission spectrum (thick line) htted according to Eq. (1) (thin line) gives a sample temperature of 3000 K.

When the frequency of a laser falls fully into an absorption band, multiple phonon processes start to appear. Leite et al 2° ) observed /7 h order ( = 1, 2. 9) Raman scattering in CdS under conditions of resonance between the laser frequency and the band gap or the associated exciton states. The scattered light spectrum shows a mixture of fluorescent emission and Raman scattering. Klein and Porto 207) associated the multiphonon resonance Raman effect with the fluorescent emission spectrum, and suggested a possible theoretical approach to this effect. 

Most of the solid-state lasers employ as active material crystals or glasses doped with rare-earth or actinide ions, because these ions exhibit a large number of relatively sharp fluorescent lines, covering the whole visible and near-infrared spectrum 380) search for new laser materials and investigations of the characteristics of laser emission at different temperatures of the active material and with various pump sources have improved knowledge about the solid state spectra and radiationless transitions in laser media 38i). 

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