Ultra-narrow-linewidth continuous-wave THz sources based on multiplier chains

Abstract

We demonstrate two different sources at 1.3 THz based on multiplier chains (72nd harmonic generation), which exhibit linewidths at the level of 2 × 10 −12 in relative units. The multiplication processes are shown not to contribute significantly to this linewidth. The phase noise of one of the sources and the fractional power in the carrier (76%) were determined. The application of these sources as references for quantum cascade THz lasers and for spectroscopy of ultracold molecules is suggested. Thus, rotational spectroscopy with few Hz resolution at 1.3 THz is possible with the present easy-to-use sources. An approach for reducing the linewidth by a factor on the order of 10 3 to the 1 × 10 −15 level using optical technology is proposed.

Rotational spectroscopy of cold and trapped molecular ions in the Lamb–Dicke regime

“…6 shows the line width of the difference frequency signal, which is 86 mHz. Based on this value and previous characterizations [41], we estimate a line width < 10 Hz at 1.3 THz. We can also infer the long-term frequency stability of the THz wave, by comparing the maser frequency to a GPS-derived 1 PPS signal and to a cryogenic silicon optical resonator [43].…”

“…The THz system consists of a hydrogen maser, whose frequency, f H 1.4 GHz, is downconverted to 10 MHz and then used as reference for a microwave synthesizer operating at f mmw/72 = 18.262 GHz. Its output is converted in a ×72 multiplier/amplifier chain to f rot =1.31 THz [41]. We verified the high spectral purity of the THz wave at the intermediate frequency 18.251 GHz, close to f mmw/72 .…”

From megahertz to terahertz qubits encoded in molecular ions: theoretical analysis of dipole-forbidden spectroscopic transitions in N2+

“…The sensitivity of these transitions to the proton-to-electron mass ratio 69 renders them interesting for testing a possible time variation of these fundamental constants as they are within the reach of stabilized THz sources. 70 In general, M1 S transition selection rules do not permit a change of rotational quantum numbers by DN = 2, but this mechanism must still be considered due to mixing of rotational states. In addition, the anisotropy of the electron-spin g-factor tensor allows for DN = 2 transitions through M1 aS coupling.…”

Monolithically Integrated DFB Lasers for Tunable and Narrow Linewidth Millimeter-Wave Generation

“…The technologies available to date for the generation of continuous wave (CW) mm-wave and THz signals span from electronics [5] to photonics [6]. Traditional electronic approaches include impact avalanche transit time diodes, Gunn diodes, and frequency multipliers, and are capable of achieving ≈1 Hz linewidth, at the expense of a bulky setup and poor tunability [7]. More recent microelectronic circuit technologies have enabled the demonstration of oscillators at hundreds of gigahertz with good power efficiency, but still with a very limited tunability [8], [9].…”