Two-colour diode lasers for generation of THz radiation

Abstract

Direct emission of terahertz (THz) radiation out of a two-colour semiconductor laser is reported and analysed. The geometry of the tunable two-colour laser is described together with the physical mechanisms responsible for the emission at the THz difference frequency of the two pump colours used. On the basis of this analysis, different possibilities are suggested to increase the emitted THz intensity towards application relevant levels.

Semiconductor laser based THz generation and detection

“…A few years ago, we have shown that two-colour diode lasers emit directly the THz difference frequency of the two colours [16]. We have discussed possible strategies for increasing the generated power via this direct THz generation and our estimations show that with some technological effort into the device design the generated power may reach the µW range and thus become competitive with that of external photomixing systems [17]. To analyse the obtainable bandwidth of this concept, we made use of the fact that the nonlinearity responsible for the direct THz generation also results in the generation of four-wave mixing (FWM) sidebands which are easily visible in the near infrared optical spectra.…”

Generation of Terahertz radiation with two color semiconductor lasers

“…Accordingly, one has to perform an extensive analysis of means how to improve the experimental setup and, in particular, the diode laser design to achieve application relevant power levels. We now extend the first analysis given in [59] in order to find out whether application relevant power levels in the range above 1 µW can be achieved at all: A first major improvement of the direct emission approach can be achieved with a modification of the cavity geometry of the two color laser. Matus et al have analyzed this laser system theoretically and showed that the spectral purity of the two color emission is crucial for the nonlinear frequency mixing of the two colors [61].…”

“…Then, the normalized bolometer signal for the operation on one color only is subtracted from the two-color signal to extract the specific contribution due to two-color operation. Further details on this normalization procedure are given in [59]. Our data for the normalized THz signal as a function of the difference frequency ν 21 are shown by the red dots in Fig.…”

“…A concept for a two color Littman laser without intracavity beam splitter is suggested e.g. in [59]. Another option for pure coherent two color lasers is to use diode lasers without external cavity but with internal spectral filter elements that enable simultaneous two color operation.…”

Dual-wavelength high-power diode laser system based on an external-cavity tapered amplifier with tunable frequency difference

“…Dual-wavelength diode laser systems are attractive for many applications, such as dual-wavelength interferometry, optical switching, terahertz (THz) radiation generation, and THz imaging [1][2][3][4][5]. Different techniques have been developed to achieve dual-wavelength operation of a diode laser system, and they mainly can be classified into two categories: (1) Monolithic dual-wavelength diode lasers [6][7][8][9][10], and (2) diode laser systems based on different external-cavity feedback techniques [11][12][13][14][15][16][17].…”