Differential photoconductive sampling with a resolution independent of carrier lifetime

We present a novel approach to photoconductive sampling with a resolution which is virtually independent of the carrier lifetime and is governed solely by the circuit-limited gap charging time. Using photoconductors with a carrier lifetime of 150 ps, accurate measurement of a 65-ps-wide electrical signal is demonstrated and the actual resolution is believed to be 10 ps

The laser

This article is intended as a review of the field of optical masers, or lasers as they have come to be known, summarizing both theory and practice. It starts with a theoretical section in which black body radiation theory is used to introduce the concepts of spontaneous and induced transitions. This is followed by the derivation of the Schawlow-Townes instability (start-oscillation) condition and a description of the different laser media. Other topics treated include: optical pumping, experimental techniques, output power and noise. The sections on optical resonators and communications which conclude the paper have been slightly emphasized since, perhaps to a larger extent than the other topics covered in this paper, they coincide with traditional areas of interest of microwave and communications engineers

Heating from Continuous Number Density Measurements in Optical Lattices

We explore the effects of continuous number density measurement on atoms in an optical lattice. By integrating a master equation for quantum observables, we calculate how single particle correlations decay. We consider weakly- and strongly- interacting bosons and noninteracting fermions. Even in the Mott regime, such measurements destroy correlations and increase the average energy, as long as some hopping is allowed. We explore the role of spatial resolution, and find that the heating rate is proportional to the amount of information gained from such measurements.Comment: 10 pages, 4 figure

A Noise Investigation of Tunnel-Diode Microwave Amplifiers

An analysis and derivation of the noise figure of a tunnel-diode microwave amplifier are presented. The agreement between the measured noise figure and the theoretical results is an indirect check on the existence of full shot noise in germanium tunnel diodes at microwave frequencies. The limiting noise temperature of the amplifier is eI0R/2k, and can be approached by using diodes with small (RC) products in which the extreme overcoupling (load mismatch) and high gain can be achieved simultaneously

Intermodal stability of a coupled-cavity semiconductor laser

We present an analysis of the steady-state operation of a two-element coupled-cavity laser near a mode hop. The equations of motion for the two cavities and two relevant modes of a longitudinally coupled-cavity laser are reduced to a system of nondimensional nonlinear ordinary differential equations which describe a general two-element laser. The equations are then solved and the stability of their solutions is analyzed. Depending upon the fill factors for the two modes, there exists an intrinsically multimode oscillation for operating conditions under which it was previously thought that no steady state existed. Under conditions where the multimode state is unstable, both of the single-mode states are stable with bistable transitions occurring only on the boundaries of the unstable multimode regimes

Coupling coefficients for coupled-cavity lasers

We derive simple, analytic formulas for the field coupling coefficients in a two-section coupled-cavity laser using a local field rate equation treatment. We show that there is a correction to the heuristic formulas based on power flow calculated by Marcuse; the correction is in agreement with numerical calculations from a coupled-mode approach

Analysis of the dynamic response of multielement semiconductor lasers

We present a derivation of the dynamic response of a semiconductor laser consisting of more than one active element. We show that the amplitude and phase of the modulated cavity adiabatically follows the complex resonance of the composite cavity; and using this relation, plus linearized carrier equations, we calculate the parameters characterizing the modulation response of the composite system. In the process, "effective" differential gain constants and linewidth enhancement factors arise which take the place of the corresponding parameters in single-element lasers. In the case of a two-section laser, we show that frequency chirping under modulation is present except under special conditions; we identify those conditions and show how chirping can be avoided

Experimental Procedure for the Determination of the Number of Paramagnetic Centers

The determination of the number of paramagnetic centers in a given crystal is usually performed by comparing the resonance signal of the unknown centers with that of a calibrated standard. The two most often used standards are CuSO4·5H2O and DPPH. In the procedure described below the number of "spins" is obtained from a measurement of the reflection coefficient of a reflection cavity containing the spins; or more specifically from the change in the reflection coefficient between the "on resonance" and "off resonance" conditions. The measurements can be performed with the aid of the conventional equipment for the measurement of reflection coefficients. Great simplification is realized when a variable coupling cavity [1] is used

Radiation Damping Effects in Two Level Maser Oscillators

Several experiments [1,2] have noted recently that when an inverted two-level spin system was permitted to radiate spontaneously, the resulting oscillation was characterized by an appreciable amplitude modulation. The phenomenon was first believed to be the result of interference of different spin packets in an inhomogeneously broadened spectrum [1]. A theoretical analysis (which will be reported separately) shows that this is not the case. The spins are not independent but are coupled together by means of their radiation field. This explanation has since been by its original authors