Available online at http://www.idealibrary.com on Article No. spmi.1999.0761 Superlattices and Microstructures, Vol. 26, No. 2, 1999 Direct time domain observation of exciton–polariton oscillation in a semiconductor microcavity S HUDONG J IANG,S USUMU MACHIDA,YOSHIHIRO TAKIGUCHI ERATO Quantum Fluctuation Project, NTT Musashino R&D Center, 3-9-11 Midori-cho, Musashino-shi, Tokyo 180-0012, Japan YOSHIHISA YAMAMOTO ERATO Quantum Fluctuation Project, E. L. Ginzton Laboratory, Stanford University, Stanford, CA 94305, U.S.A. HUI CAO Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3112, U.S.A. (Received 7 May 1999) We measured temporal evolution of the coherent emission from a semiconductor micro- cavity by an ac-balanced homodyne detector with high sensitivity and wide dynamic range. The experimental results can be well explained by the coupled exciton–photon model. c  1999 Academic Press Key words: time domain observation, exciton–polariton oscillation, microcavity, balanced homodyne detection, femtosecond. 1. Introduction Over the past few years, there have been extensive study of the coupled exciton–photon system in a quan- tum well (QW) embedded semiconductor microcavity. The experimental investigation was carried out in the spectral measurement [1–3], direct time domain measurement [4–6] and four-wave mixing experiment [9]. We used an ac-balanced homodyne detection (AC-BHD) technique to directly observe dynamic behaviors of an exciton–photon system [7, 8]. The advantages of the ac-balanced homodyne detection technique are: femtosecond resolution, high sensitivity, and large dynamic range [10]. 2. ac-balanced homodyne detection The basic set-up of the AC-BHD system is configured as shown in Fig. 1. Optical pulses with a duration of 150 fs, generated by a fs Ti : sapphire mode-lock laser, were injected into a Mach–Zehnder interferometer and split into two beams at a beam splitter (BS1). One beam is used as a local oscillator wave while the other is as a signal wave. The signal pulses with a relative time delay τ generated by a corner mirror (CM2) is recombined with the local oscillator pulse at the second beam splitter (BS2). For suppressing intensity noise of the incident optical pulses, a balanced homodyne detection configuration with two photodiodes PD1 0749–6036/99/080073 + 10 $30.00/0 c  1999 Academic Press