Before the 1960s, all anti-Stokes emissions, which were known to exist, involved emission energies in excess of excitation energies by only a few kT. They were linked to thermal population of energy states above excitation states by such an energy amount. It was the well-known case of anti-Stokes emission for the so-called thermal bands or in the Raman effect for the well-known anti-Stokes sidebands. Thermoluminescence, where traps are emptied by excitation energies of the order of kT, also constituted a field of anti-Stokes emission of its own. Superexcitation, i.e., raising an already excited electron to an even higher level by excited-state absorption (ESA), was also known but with very weak emissions. These types of well-known anti-Stokes processes have been reviewed in classical textbooks on luminescence.1 All fluorescence light emitters usually follow the well-known principle of the Stokes law which simply states that excitation photons are at a higher energy than emitted ones or, in other words, that output photon energy is weaker than input photon energy. This, in a sense, is an indirect statement that efficiency cannot be larger than 1. This principle is

Upconversion and Anti-Stokes Processes with f and d Ions in Solids

The various arguments for introducing optical interconnections to silicon CMOS chips are summarized, and the challenges for optical, optoelectronic, and integration technologies are discussed. Optics could solve many physical problems of interconnects, including precise clock distribution, system synchronization (allowing larger synchronous zones, both on-chip and between chips), bandwidth and density of long interconnections, and reduction of power dissipation. Optics may relieve a broad range of design problems, such as crosstalk, voltage isolation, wave reflection, impedence matching, and pin inductance. It may allow continued scaling of existing architectures and enable novel highly interconnected or high-bandwidth architectures. No physical breakthrough is required to implement dense optical interconnects to silicon chips, though substantial technological work remains. Cost is a significant barrier to practical introduction, though revolutionary approaches exist that might achieve economies of scale. An Appendix analyzes scaling of on-chop global electrical interconnects, including line inductance and the skin effect, both of which impose significant additional constraints on future interconnects.

/pdf/rationale-and-challenges-for-optical-interconnects-to-5clh2238g9.pdf

Rationale and challenges for optical interconnects to electronic chips

Polymer composites are one of the most attractive near-term means to exploit the unique properties of carbon nanotubes and graphene. This is particularly true for composites aimed at electronics and photonics, where a number of promising applications have already been demonstrated. One such example is nanotube-based saturable absorbers. These can be used as all-optical switches, optical amplifier noise suppressors, or mode-lockers to generate ultrashort laser pulses. Here, we review various aspects of fabrication, characterization, device implementation and operation of nanotube-polymer composites to be used in photonic applications. We also summarize recent results on graphene-based saturable absorbers for ultrafast lasers.

Nanotube–Polymer Composites for Ultrafast Photonics

In order to enable optical systems to operate with a high degree of compactness and reliability it is necessary to combine large number of optical functions in small monolithic structures. A development, somewhat reminiscent of that that took place in Integrated Electronics, is now beginning to take place in optics. The initial challenge in this emerging field, known appropriately as "Integrated Optics", is to demonstrate the possibility of performing basic optical functions such as light generation, coupling, modulation, and guiding in Integrated Optical configurations. The talk will review the main theoretical and experimental developments to date in Integrated Optics. Specific topics to be discussed include: Material considerations, guiding mechanisms, modulation, coupling and mode losses. The fabrication and applications of periodic thin film structures will be discussed.

Integrated optics

The emission and absorption properties of numerous host crystals doped with Yb/sup 3+/ ions have been studied. The hosts which have been selected include LiYF/sub 4/, LaF/sub 3/, SrF/sub 2/, BaF/sub 2/, KCaF/sub 3/, KY/sub 3/F/sub 10/, Rb/sub 2/NaYF/sub 6/, BaY/sub 2/F/sub 8/, Y/sub 2/SiO/sub 5/, Y/sub 3/Al/sub 5/O/sub 12/, YAlO/sub 3/, LuPO/sub 4/, Ca/sub 5/(PO/sub 4/)/sub 3/F, LiYO/sub 2/, and ScBO/sub 3/. Spectral determinations have been made of the resonant absorption and emission cross sections between 850 and 1100 nm, and the emission decay times of the upper laser level have been measured. The emission cross sections have been evaluated using the absorption cross section and principle of reciprocity, and again using the Fuchtbauer-Ladenberg formula. Agreement between the two methods is within 20% for most materials. The results are discussed in the framework of requirements for an effective diode-pumped Yb/sup 3+/ laser system. Ca/sub 5/(PO/sub 4/)/sub 3/F:Yb is predicted to exhibit the most useful laser properties and is expected to be far superior to Y/sub 3/Al/sub 5/O/sub 12/:Yb in many key microscopic parameter values. >

Evaluation of absorption and emission properties of Yb/sup 3+/ doped crystals for laser applications

We have carried out a detailed spectroscopic characterization of Nd: GdVO4, a new laser crystal with high effective absorption and emission cross sections. The accidental degeneracy of the upper4
F
3/2 laser level decreases the number of emission lines and creates -together with the anisotropic crystal field - high emission cross sections (7.6 × 10−19 cm2 at 1.06 µm and 300 K). In addition, the lines are strongly homogeneously broadened (1.6 nm for the 808.4 nm diode-laser pump transition). The temperature dependences of lifetime, linewidths, and cross sections have been determined. Slope efficiencies up to 57% with respect to the absorbed diode-laser pump power and output powers up to 0.8 W have been achieved at 1.06 µm from a 2 mm long crystal. Intracavity second-harmonic generation, using a KTP crystal, is demonstrated.

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

Single crystals of gadolinium vanadate doped with neodymium ions have been grown by the Czochralski method. The absorption and luminescence spectra of the neodymium have been measured. The absorption near 0.8 μm is higher than 70 cm−1. The lifetime of the neodymium ions is 90 μs. Laser action has been achieved on the transitions 4F3/2 → 4I13/2, 4I11/2. The differential efficiency of the lasing near 1.06 μm is 54%.

https://iopscience.iop.org/article/10.1070/QE1992v022n12ABEH003672/pdf

The Nd:GdVO4 crystal: a new material for diode-pumped lasers

The refractive indices of new Nd3+ : GdVO4, Tm3+ : GdVO4, and Er3+ : GdVO4 laser crystals were determined with an error of ±5×10-5 in the range 400–1100 nm. The birefringence of these crystals was on the average 0.24, and the dispersion was described by the formula 1/Δn2 = a+ b/λ2. The thermal conductivity of the Nd : GdVO4 crystal (atomic neodymium concentration 1.3%) was determined in the temperature range 77-300 K. At 300 K the conductivity along the direction was 11.7 W m-1 K-1, which was higher than the conductivity of Nd : YAG crystals.

https://iopscience.iop.org/article/10.1070/QE1995v025n12ABEH000556/pdf

GdVO4 as a new medium for solid-state lasers: some optical and thermal properties of crystals doped with Cd3+, Tm3+, and Er3+ ions

In garnets doped with chromium and rare-earth ions, the processes of energy transfer, including upconversion, were investigated. Their influence on laser properties is established.

Non-linear population processes of Er3+ laser levels in chromium-doped garnet crystals

We report for the first time on tunable room temperature cw laser action of a transition metal laser material In Cr3+:GdScGa-garnet crystals almost the total fluorescence is channelled into the broad band4
T
2→4
A
2 transition The fluorescence lifetime is τ=120 μs Laser pumping in the blue-green and yellow-red spectral range yields pump thresholds around 250 mW and slope efficiencies up to 11% The wavelength of the free running Cr3+ laser is centered at 777 nm

Ivan A Shcherbakov

Papers

Spectroscopic characterization and laser performance of diode-laser-pumped Nd: GdVO4

The Nd:GdVO4 crystal: a new material for diode-pumped lasers

GdVO4 as a new medium for solid-state lasers: some optical and thermal properties of crystals doped with Cd3+, Tm3+, and Er3+ ions

Non-linear population processes of Er3+ laser levels in chromium-doped garnet crystals

Tunable room-temperature cw laser action in Cr 3+ : GdScGa-Garnet