Heterodyne Spectroscopy of Frequency Instabilities in Terahertz Quantum-Cascade Lasers Induced by Optical Feedback

Hübers, Heinz‐Wilhelm; Richter, Heiko; Eichholz, René; Wienold, Martin; Biermann, K.; Schrottke, L.; Grahn, H. T.

doi:10.1109/jstqe.2017.2684078

Cited by 16 publications

(17 citation statements)

References 25 publications

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“…From the value þ7.2 MHz/mA given in Ref. 47 and the area of the laser ridge of 0.12 Â 1.4 mm 2 for the singlemode QCL, we obtain a tuning coefficient of about þ12 MHz/(A cm À2 ), which is in reasonable agreement with the result for the multi-mode QCL within the accuracy of our model. However, the smaller tuning coefficient for the (longer) multi-mode lasers indicates a possible interaction of the modes in these lasers.…”

Section: Discussionsupporting

confidence: 88%

“…Finally, we compare the observed tuning behavior with tuning coefficients for single-mode lasers operating in continuous-wave mode as reported in Ref. 47. These lasers are based on the same wafers as for QCLs A2 and B2.…”

Section: Discussionmentioning

confidence: 85%

“…6(b) for the mode at 4.76 THz between current densities of 370 and 600 A/cm 2 so that the tuning coefficient is about À20 MHz/(A cm À2 ). The tuning coefficient for the corresponding single-mode QCL with laser dimensions of 0.08 Â 1.3 mm 2 is À60 MHz/mA, 47 which leads to a value of about À60 MHz/(A cm À2 ). In order to verify this surprisingly large value, we consider also the behavior of another laser made from the same wafer, which was reported in Ref.…”

Section: Discussionmentioning

confidence: 99%

See 2 more Smart Citations

Intrinsic frequency tuning of terahertz quantum-cascade lasers

Schrottke

Lü

Röben

et al. 2018

Journal of Applied Physics

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We have studied the intrinsic frequency tuning of several terahertz (THz) quantum-cascade lasers (QCLs) based on a hybrid design. With increasing driving current, most QCLs exhibit either a redshift or a blueshift, while some QCLs show both. An oscillator model describes the observed behavior. The accuracy of the model is affected by the complexity of the current-dependent gain spectra of the THz QCLs. Numerical simulations demonstrate a cavity pulling effect insofar as the tuning behavior depends on the resonator losses and on the width of the gain spectra.

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Section: Discussionsupporting

confidence: 88%

Section: Discussionmentioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

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Intrinsic frequency tuning of terahertz quantum-cascade lasers

Schrottke

Lü

Röben

et al. 2018

Journal of Applied Physics

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“…Most application scenarios rely on mechanical cryocoolers instead of flow cryostats [3]. This typically implies a significant level of cooler vibrations, which were identified as a source of frequency fluctuations [18,20]. We found that a Lamb dip signal is still observable under such conditions, if the measurement is synchronized to the fundamental frequency of the cooler vibration.…”

Section: Doppler-free Spectroscopy In the Presence Of Cooler Vibratiomentioning

confidence: 82%

Doppler-free spectroscopy with a terahertz quantum-cascade laser

et al. 2018

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We report on the Doppler-free saturation spectroscopy of a molecular transition at 3.3 THz based on a quantum-cascade laser and an absorption cell in a collinear pump-probe configuration. A Lamb dip with a sub-Doppler linewidth of 170 kHz is observed for a rotational transition of HDO. We found that a certain level of external optical feedback is tolerable as long as the free spectral range of the external cavity is large compared to the width of the absorption line.

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“…Recent studies have shown that the intrinsic quantum limit for the linewidth of THz QCLs lies in the sub-kHz range [5,6]. However, the practical linewidth for a free-running THz QCL is much larger, which is due to the limited stability of the driving current and temperature as well as to optical feedback [7]. In practice, the emission frequency drift can exceed 10 MHz [8,9].…”

Section: Introductionmentioning

confidence: 99%

Frequency and power stabilization of a terahertz quantum-cascade laser using near-infrared optical excitation

Alam¹,

Wienold²,

Lü³

et al. 2019

Opt. Express

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We demonstrate a technique to simultaneously stabilize the frequency and output power of a terahertz quantum-cascade laser (QCL). This technique exploits frequency and power variations upon near-infrared illumination of the QCL with a diode laser. It does not require an external terahertz optical modulator. By locking the frequency to a molecular absorption line, we obtain a long-term (one-hour) linewidth of 260 kHz (full width at half maximum) and a root-mean-square power stability below 0.03%. With respect to the free-running case, this stabilization scheme improves the frequency stability by nearly two orders of magnitude and the power stability by a factor of three.

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Heterodyne Spectroscopy of Frequency Instabilities in Terahertz Quantum-Cascade Lasers Induced by Optical Feedback

Cited by 16 publications

References 25 publications

Intrinsic frequency tuning of terahertz quantum-cascade lasers

Intrinsic frequency tuning of terahertz quantum-cascade lasers

Doppler-free spectroscopy with a terahertz quantum-cascade laser

Frequency and power stabilization of a terahertz quantum-cascade laser using near-infrared optical excitation

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