Solid state oscillators

The noise, both AM and FM, of microwave oscillators used in ESR bridges is equal to or worse than in early years. There has been little improvement in tube oscillators and solid state oscillators have somewhat worse noise in our experience. It is important to recognize that both oscillator AM and FM noise are enhanced in a microwave bridge of the reference arm type. Wilmshurst [12] discusses AM noise enhancement, deriving the following equation for the noise voltage... 

Dipole oscillations in an assembly of molecules in the membrane of cells can be modeled as phase-locked solid state oscillators by a basic circuit as in Figure 1. Loose coupling between such circuits imposes an eigenvalue problem from which significant mode softening can be shown to result and this has been suggested to be an important requirement in the energetics associated with the reproduction and mutation of cells. As each individual unit oscillator can operate at subharmonics as well as harmonics, the above model is consistent with the idea that in vivo a number of discrete frequencies exist in the cell. 

Microwave spectroscopy uses tunable coherent sources of radiation such as microwave synthetizers, solid state oscillators (Gunn diodes) or electronic tubes (klystrons). These oscillators can be operated in their fundamental mode (up to 120 GHz) but harmonic generation is commonly realized with frequency multipliers up to 500 GHz, and has been used to reach 1 THz on occasions. Backward wave oscillators are available up to 1.2 THz in their fundamental mode. Figures 1 and 2 show typical rotational spectra recorded with this type of sources. Different techniques can be used to work in the THz region ... 

Fig. 1 shows the block diagram of the vibrometer, in which the most sensible to small phase variations interferometric scheme is employed. It consists of the microwave and the display units. The display unit consists of the power supply 1, controller 2 of the phase modulator 3, microprocessor unit 9 and low-frequency amplifier 10. The microwave unit contains the electromechanical phase modulator 3, a solid-state microwave oscillator 4, an attenuator 5, a bidirectional coupler 6, a horn antenna 7 and a microwave detector 11. The horn antenna is used for transmitting the microwave and receiving the reflected signal, which is mixed with the reference signal in the bidirectional coupler. In the reference channel the electromechanical phase modulator is used to provide automatic calibration of the instrument. To adjust the antenna beam to the object under test, the microwave unit is placed on the platform which can be shifted in vertical and horizontal planes. 

These limitations have recently been eliminated using solid-state sources of femtosecond pulses. Most of the femtosecond dye laser teclmology that was in wide use in the late 1980s [11] has been rendered obsolete by tliree teclmical developments the self-mode-locked Ti-sapphire oscillator [23, 24, 25, 26 and 27], the chirped-pulse, solid-state amplifier (CPA) [28, 29, 30 and 31], and the non-collinearly pumped optical parametric amplifier (OPA) [32, 33 and 34]- Moreover, although a number of investigators still construct home-built systems with narrowly chosen capabilities, it is now possible to obtain versatile, nearly state-of-the-art apparatus of the type described below Ifom commercial sources. Just as home-built NMR spectrometers capable of multidimensional or solid-state spectroscopies were still being home built in the late 1970s and now are almost exclusively based on commercially prepared apparatus, it is reasonable to expect that ultrafast spectroscopy in the next decade will be conducted almost exclusively with apparatus ifom conmiercial sources based around entirely solid-state systems. 

E. L. HoEman, Solid-State Microwave Power Oscillator Design, Artech House, Boston, Mass., 1992. 

At frequencies higher than this, a solid-state counter must be used. This is based on a stable oscillator and, in effect, counts the pulses generated during one cycle of the supply frequency. The range and accuracy of the instrument depends on the master oscillator frequency, but units capable of use over the whole range up to 600 MHz... 

Lick Observatory. The success of the LLNL/AVLIS demonstration led to the deployment of a pulsed dye laser / AO system on the Lick Observatory 3-m telescope (Friedman et al., 1995). LGS system (Fig. 14). The dye cells are pumped by 4 70 W, frequency-doubled, flashlamp-pumped, solid-state Nd YAG lasers. Each laser dissipates 8 kW, which is removed by watercooling. The YAG lasers, oscillator, dye pumps and control system are located in a room in the Observatory basement to isolate heat production and vibrations from the telescope. A grazing incidence dye master oscillator (DMO) provides a single frequency 589.2 nm pulse, 100-150 ns in length at an 11 kHz repetition rate. The pulse width is a compromise between the requirements for Na excitation and the need for efficient conversion in the dye, for which shorter pulses are optimum. The laser utilizes a custom designed laser dye, R-2 perchlorate, that lasts for 1-2 years of use before replacement is required. 

In the Introduction the problem of construction of a theoretical model of the metal surface was briefly discussed. If a model that would permit the theoretical description of the chemisorption complex is to be constructed, one must decide which type of the theoretical description of the metal should be used. Two basic approaches exist in the theory of transition metals (48). The first one is based on the assumption that the d-elec-trons are localized either on atoms or in bonds (which is particularly attractive for the discussion of the surface problems). The other is the itinerant approach, based on the collective model of metals (which was particularly successful in explaining the bulk properties of metals). The choice between these two is not easy. Even in contemporary solid state literature the possibility of d-electron localization is still being discussed (49-51). Examples can be found in the literature that discuss the following problems high cohesion energy of transition metals (52), their crystallographic structure (53), magnetic moments of the constituent atoms in alloys (54), optical and photoemission properties (48, 49), and plasma oscillation losses (55). 

Enhancement of x2 will lead to improvement (in terms of efficiency per interaction volume) in the following applications up-conversion in the visible or near U.V. of powerful I.R. laser radiation, frequency modulation of a laser carrier beam, optical parametric oscillation and amplification for solid state infrared tunable coherent devices. 

In addition to the above prescriptions, many other quantities such as solution phase ionization potentials (IPs) [15], nuclear magnetic resonance (NMR) chemical shifts and IR absorption frequencies [16-18], charge decompositions [19], lowest unoccupied molecular orbital (LUMO) energies [20-23], IPs [24], redox potentials [25], high-performance liquid chromatography (HPLC) [26], solid-state syntheses [27], Ke values [28], isoelectrophilic windows [29], and the harmonic oscillator models of the aromaticity (HOMA) index [30], have been proposed in the literature to understand the electrophilic and nucleophilic characteristics of chemical systems. 

A useful source of continuously tunable radiation from the near UV to the near-IR with unexplored potential in fluorescence studies is the optical parametric oscillator (OPO). These devices have been around since the 1960s(73) and have received a lot of coverage recently in laser and optoelectronic journals/74 This resurgence of interest in OPOs has been brought about by recent improvements in nonlinear crystals and the development of all-solid-state pump-laser sources with the required levels of coherence and intensity. 

M. Ebrahimzadeh, G. J. Hall and A. I. Ferguson, Singly resonant, all-solid-state, mode-locked LiBaOs optical parametric oscillator tunable from 652nm to 2650nm, Optics Lett. 17, 652-654 (1992). 

We will restrict our description to those processes and systems that have been developed more over recent years those based on the optical parametric oscillation or amplification processes. The practical devices involve two of the most relevant solid state lasers nowadays the Nd YAG laser and the Ti-sapphire laser. 

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