Organic laser breakthrough
Jul 31, 2000
NB: The publications on which this article is based have been retracted by their authors. The retractions followed an investigation into scientific misconduct by J Hendrik Schön. We are leaving this article here for archival purposes. Further information can be found at http://physicsweb.org/article/news/6/9/15
The first electrically powered organic laser has been demonstrated by physicists at Bell Laboratories in the US (J H Schön et al Science 289 599). The new device uses a tetracene crystal, which consists of four benzene rings linked together, and conducts electricity well. Lasers based on organic semiconductors will be easier and cheaper to manufacture than existing devices that rely on conventional inorganic semiconductors. Laser action has previously been observed in many semiconducting polymers and single crystals, but the emitted light was stimulated by other lasers. The new system represents the first electrically pumped organic laser. Electrically pumped lasers are desirable because they are more compact and can be integrated into complex electronic circuitry.
Hendrik Schön and co-workers grew the single tetracene crystal from the vapour phase and surrounded it with field-effect transistors to produce electron- and hole-rich regions in the crystal. By applying a 5 V potential difference across the crystal, the team caused the positive and negative charges to flood across the crystal and recombine, producing a burst of photons that initiated the lasing process. The cleaved ends of the crystal act as the reflecting endpoints of the laser cavity, amplifying the emission to produce yellowy-green light with a wavelength of 575.7 nm.
Schön and coworkers believe they can reduce the optical losses in their present system to substantially lower the threshold current density needed for laser action. This will bring a room temperature continuous tetracene-based laser another step closer.
The group previously demonstrated the fractional quantum Hall effect in tetracene crystals (Science 288 2338), and the new organic laser is the latest in a string of achievements from Schön and his colleagues.