Frequency-up conversion

A number of other up-conversion processes are known. The blue emission from a Yb3+/Tm3+ couple in which the active emitters are defect Tm3+ centers is mainly due to the efficient excitation ET process from Yb3+ centers. Two-frequency up-conversion has been investigated using Pr3+ defects in a fluoride glass matrix. Illumination with one pump wavelength results in GSA, while simultaneous irradiation with a second pump wavelength further excites the GSA centers via ESA. The doubly excited defects emit red light. Up-conversion and visible output only takes place at the intersection of the two beams. 

Optical frequency up-conversion, or second harmonic generation (SHG), in nanostructured surfaces can be also considered as a kind of field enhance-menf [61]. In general, SHG efficiency is proportional to the square of nonlinear polarization ha (x [P (2second order susceptibility. For a nanostructured surface, the incident field is transformed to the local field given by Eq. 19, yielding ... 

U.v. laser excitation of high vibrational levels of CO(X 2 ) was shown to produce VUV emission from CO(A n). The possibility of making use of this frequency up-conversion in a CO electronic laser was discussed. The rotational relaxation of C 0(A lI),t) = 13, J = 13 by various gases has been described by Vikis. Relaxation rates were found to correlate with the reduced mass of the quencher for all collision partners except Xe, and for... 

Frequency up-converted lasing is an important research area and has become more promising in recent years because this technique provides several main advantages when compared to other coherent frequency up-conversion techniques ... 

Although the two-photon chromphores mentioned above provide high two-pho-ton absorption cross-section values and stronger frequency up-conversion emission than commercialized dyes, there are two major drawbacks for using these molecular materials for applications ... 

For frequency up-conversion lasing application, we have synthesized a partially cross-linked, fluorescent polymer system and demonstrated the two-photon... 

The early experimental studies on LICS involved polarization-rotation, frequency-up conversion, third-harmonic generation, and multiphoton ionization. The progress was hampered initially because a LICS experiment is rather demanding on resources it requires two frequency-stable tunable lasers, at least one of which must be sufficiently intense to embed a bound state in the continuum in the presence of processes that degrade the LICS signatures, such as spontaneous emission. A difficulty associated with the observation of LICS is due to the change in the effective coupling over the... 

Early demonstrations of LICS were also done in frequency up-conversion... 

At present the resonant six wave mixing in Ar and Ne is subject of detailed investigations. The results obtained so far indicate that the mixing schemes described above are appropriate for the desired extension of the tuning range of the VUV light generated by nonlinear frequency up-conversion. 

A prominent example of the latter is harmonic generation or frequency up-conversion. Here, a high-quality long wavelength laser beam is converted to the soft X-ray region through the nonlinear response of certain transmitting... 

VI. OPTICAL PHASE CONJUGATION WITH FREQUENCY UP-CONVERSION VIA HIGH-ORDER, NON-DEGENERATE MULTIHAVE MIXING [is]... 

Fig. 1.41 (a) Relation between the incident light intensity and the frequency up-converted iight intensity, (b) Illustration of the two-step excitation and subsequent light emission, (c) Efficiency of the frequency up-conversion as a function of the incident light power density. For comparison, the efficiency of the second harmonic generation from a KDP crystal is tilso shown... 

Instead of the powdery grains of organic dye molecules, a variety of materials can be used for optical frequency up-conversion so long as the DP-CPs are efficiently generated on their surfaces. 

The DP-CP can be used to convert optical energy to electrical energy with frequency up-conversion. This section reviews two examples. 

Photonic Applications. Several areas of application of glass-ceramic materials are emerging in the photonic and optical communications fields. These include lasers and frequency up-conversion devices in which the optical advantages of fluorescent rare-earth ions in crystalline host materials are combined with manufacturing and structural advantages of glass. Their technical importance and commercial impact is not yet clear. 

As is known, Er Afb co-doped materials have been recognized as one of the most efficient systems for obtaining frequency up-conversion photoluminescence due to the efficient energy transfer from Yb to Er ions pmnped by 980 nm [68,69], in which Er ions acted as luminescence centers and Yb ions as sensitizers. On the other hand, considering the lattice structure of BiT, Er AT) ions can be accommodated in well defined sites of BiT lattice by substituting for Bi ions without the need of charge compensation. Therefore, it is of much interest to study up-conversion luminescence properties of Ei /Yb co-doped BiT thin films [70]. 

Y. Wang, J. Ohwaki, New transparent vitroceramics codoped with and Yb for efficient frequency up-conversion, J. Appl. Phys., 63, 3268-3270 (1993). 

The 2PA effect has been widely involved in numerous appheations as reviewed by Prasad et al. [25], such as frequency-up conversion lasing [26], optical power limiting [27,28], microfabrication [29,30], optical data storage and processing [31 ] and biological or medical applications [32]. As this chapter, which addresses 2PA of lanthanide complexes, will concern mainly biological applications, we will focus in this part on two-photon excited fluorescence microcopy in biology. 

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