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AIP conference proceedings

Amplification without inversion demonstrated with a coherently pumped Λ system in Cd-112

Wytze E. van der Veer, R. J. J. van Diest, A. Dönszelmann, H. B. van Linden van den Heuvell

Published Jan 1, 1993• 0 citations
Publisher

Abstract

An experiment about amplification without population inversion is discussed. The used configuration is a combination of a V and a Λ system. With a short (ns) laser pulse a coherent superposition is made, that is used afterwards as the lower state of an amplification scheme. Typical values for the gain factor and the output energy are four and hundreds of fJ, respectively.

DOI
10.1063/1.45053

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An experiment about amplification without population inversion is discussed. The used configuration is a combination of a V and a Λ system. With a short (ns) laser pulse a coherent superposition is made, that is used afterwards as the lower state of an amplification scheme. Typical values for the gain factor and the output energy are four and hundreds of fJ, respectively.
We report the observation of light amplification without population inversion. A linear superposition of an m=1 and an m=-1 magnetic substate is populated coherently. Absorption from this superposition to a higher state is canceled by interference of channels, a so-called dark resonance. An inverse transition is used for amplification of light. The temporal behavior of the amplified pulse and the gain are studied as a function of the energy splitting due to a magnetic field. In a vapor of cadmium-112 gain factors of up to 4.3 are observed.
We report the observation of steady-state amplification of a weak probe laser without population inversion in the bare states in a Doppler-broadened \ensuremath{\Lambda}-type Rb atomic system. The probe amplification was observed with the Rabi frequency of a coupling laser much smaller than the Doppler width and can be viewed as due to the dressed-state inversion. A 10% single-pass amplification of a weak probe laser was obtained, and the measured linewidth of the gain spectral feature approaches the Rb natural linewidth. A theoretical analysis based on a three-level Doppler-broadened \ensuremath{\Lambda} system is presented, and qualitative agreement with the experiment results is achieved. \textcopyright{} 1996 The American Physical Society.
The importance of lasing without inversion (LWI) in comparison with the use of nonlinear optical techniques and techniques based on high-intensity femtosecond light pulses to generate high-frequency coherent radiation is outlined. The original development and utilization of an experimental facility based on semiconductor diode lasers to study the fundamental aspects of LWI on the D1 line of the Cs atom, which is rarely attempted, is described. This experimental facility is used to observe inversionless amplification on the D1 line of the Cs atom by use of a Λ atomic scheme. A combination of EIT and broadband pumping of atoms from the lower to the upper level of the probe transition allowed the observation of the inversionless gain. Justification for the absence of inversion in the probe transition is provided. We report a single-pass inversionless gain of ≈11% with relatively weak incoherent pumping. The results show improvement over the previously reported inversionless gain observed in Na, Rb, and Cs, illustrating the potential advantage of using the D1 line of Cs.
Introduction We were able to show in Chapter 3 that a medium in which we can obtain a population inversion (i.e. a situation in which the population density in the excited state is greater than that in the fundamental level) allows for optical gain of an electromagnetic wave having a frequency near to the resonant frequency of the system. By introducing feedback of the amplified signal into the medium, the system can be made to oscillate naturally, resulting in laser oscillations . To obtain this population inversion, we must introduce at least a third (and perhaps even a fourth) energy level into the system. (We saw how a two-level system under the influence of an intense pump beam will saturate with no resulting population inversion.) The aim then of this chapter is to introduce the concepts necessary to extend our two-level system into a working model capable of illustrating the phenomenon of laser oscillation. We will not spend too much time discussing atomic transition lasers as they do not figure readily in our treatment of quantum electronic properties of semiconductors. An exception will be made, however; we brush upon the particular topics of a diode pumped laser in Complement 4.E and a quantum cascade laser in Complement 13.H. Population inversion and optical amplification Population inversion We will show how population inversion can be achieved by carrier transfer from higher lying levels to the upper level of a two-level subsystem of interest.
We report a lasing without inversion (LWI) experiment on the basis of coherent population trapping, realized in low-pressure cadmium vapor. A single-pass inversionless amplification by more than a factor of 10 has been measured, a significant improvement over previous experiments. In addition, we report synchronously pumped laser oscillation without inversion. Using a simple model to fit the gain/absorption curves as a function of magnetic field, we have obtained values for the populations in the system, showing that there is no inversion in the atomic basis. Combined with a simple optical method to measure absolute densities of a gas, this model results in a completely optical method to determine the absolute populations and density in the system.