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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 19 — Sep. 12, 2011
  • pp: 17996–18003
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Measuring frequency noise and intrinsic linewidth of a room-temperature DFB quantum cascade laser

S. Bartalini, S. Borri, I. Galli, G. Giusfredi, D. Mazzotti, T. Edamura, N. Akikusa, M. Yamanishi, and P. De Natale  »View Author Affiliations


Optics Express, Vol. 19, Issue 19, pp. 17996-18003 (2011)
http://dx.doi.org/10.1364/OE.19.017996


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Abstract

The frequency-noise power spectral density of a room-temperature distributed-feedback quantum cascade laser emitting at λ = 4.36 μm has been measured. An intrinsic linewidth value of 260 Hz is retrieved, in reasonable agreement with theoretical calculations. A noise reduction of about a factor 200 in most of the frequency interval is also found, with respect to a cryogenic laser at the same wavelength. A quantitative treatment shows that it can be explained by a temperature-dependent mechanism governing the transport processes in resonant tunnelling devices. This confirms the predominant effect of the heterostructure in determining shape and magnitude of the frequency noise spectrum in QCLs.

© 2011 OSA

1. Introduction

The interest of the scientific community in frequency-noise properties of quantum-cascade lasers (QCLs) is growing in parallel with increasing demand of such sources for high-resolution spectroscopy and frequency metrology.

In the present work, following the methods described in Ref. [1

1. S. Bartalini, S. Borri, P. Cancio, A. Castrillo, I. Galli, G. Giusfredi, D. Mazzotti, L. Gianfrani, and P. De Natale, “Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow–Townes limit,” Phys. Rev. Lett. 104, 083904 (2010). [CrossRef] [PubMed]

], we measure the FNPSD of a room-temperature (RT) QCL working at 4.36 μm and we compare it with the same quantity already measured for a cryogenic QCL at 4.33 μm. The much lower overall FNPSD, shown by the RT device, is discussed, as well as the noise contribution from the current driver. For frequencies higher than 30 MHz a white-noise region is observed, corresponding to an intrinsic linewidth of about 260 Hz. The comparison with the expected value is discussed in depth, evidencing a good agreement with the theoretical model. The dependence on temperature of both the intrinsic linewidth and the low-frequency 1/f–type FNPSD is also explained. In the last part of the paper we briefly discuss some perspectives concerning narrowing of QCL linewidth, showing that the reduced FNPSD enables to achieve sub-kHz linewidth with standard frequency-locking techniques.

2. Experimental setup

In the experiment, the frequency noise of the QCL is retrieved from a measurement of the intensity fluctuations of the laser beam after interaction with a frequency-to-amplitude converter. Following a well established method [7

7. R. M. Williams, J. F. Kelly, J. S. Hartman, S. W. Sharpe, M. S. Taubman, J. L. Hall, F. Capasso, C. Gmachl, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho, “Kilohertz linewidth from frequency-stabilized mid-infrared quantum cascade lasers,” Opt. Lett. 24, 1844–1846 (1999). [CrossRef]

, 8

8. T. L. Myers, R. M. Williams, M. S. Taubman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho, “Free-running frequency stability of mid-infrared quantum cascade lasers,” Opt. Lett. 27, 170–172 (2002). [CrossRef]

], the adopted discriminator is the side of the direct-absorption profile of a molecular transition. The spectrum of the transmitted intensity, when the laser frequency ν 0 is stabilized at the half-height position, reproduces the spectrum of the laser frequency fluctuations, scaled by the slope of the absorption profile. Fig. 1 shows the concept scheme of the experimental set-up.

Fig. 1 The schematic shows the simple experimental setup used for the measurement of the QCL frequency-noise PSD. In the inset, an acquisition of the molecular absorption profile is also shown, and the working principle of the conversion of frequency fluctuations into amplitude fluctuations is depicted.

The molecular ro-vibrational transition used in this case is the (0001–0000) P(56) line of CO2, at a constant pressure of 1 mbar. At this pressure, the conversion coefficient of 22 mV/MHz is maximum, providing the highest sensitivity. Considering the 30 nV/ Hz output voltage noise of the 200-MHz-bandwidth HgCdTe photovoltaic detector used, an ultimate sensitivity of about 2 Hz2/Hz for the FNPSD measurement is obtained. The transfer function of the discriminator is calculated for the experimental absorption profile according to the method described in [1

1. S. Bartalini, S. Borri, P. Cancio, A. Castrillo, I. Galli, G. Giusfredi, D. Mazzotti, L. Gianfrani, and P. De Natale, “Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow–Townes limit,” Phys. Rev. Lett. 104, 083904 (2010). [CrossRef] [PubMed]

].

The source is a distributed-feedback (DFB) QCL provided by Hamamatsu Photonics, with single-mode continuous-wave operation at temperatures in the range between 0 and 20 °C. The compact casing of the QCL also includes a thermo-electric cooler for efficient temperature stabilization. The beam, collimated by an aspherical ZnSe lens, is sent to a 10-cm-long cell for direct-absorption spectroscopy of CO2 gas. The absorption signal is acquired by a HgCdTe detector and processed by a real-time FFT spectrum analyzer. The chosen operating QCL temperature during the measurement is T = 15 °C. At this temperature, the threshold current is Ith = 674 mA, while the molecular resonance is found at an operating current Io = 776 mA, giving a ratio Io/Ith = 1.15. In these conditions, the laser output power is about 20 mW.

The device used in the present work is a strain-compensated In0.72Ga0.28As/In0.31Al0.69As DFB QCL [9

9. K. Fujita, T. Edamura, N. Akikusa, A. Sugiyama, T. Ochiai, S. Furuta, A. Ito, M. Yamanishi, and H. Kan, “Quantum cascade lasers based on single phonon-continuum depopulation structures,” Proc. SPIE 7230, 723016 (2009). [CrossRef]

] with 25 cascade stages, 12 μm bare ridge, 3 mm length, and an injector doping density of ∼ 2 × 1011 cm−2. The active region has a bound-to-bound quantum design, based on single phonon-continuum (SPC) depopulation [10

10. K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “Room temperature, continuous-wave operation of quantum cascade lasers with single phonon resonance-continuum depopulation structures grown by metal organic vapor-phase epitaxy,” Appl. Phys. Lett. 91, 141121 (2007). [CrossRef]

, 11

11. K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “High-performance λ ∼ 8.6 μm quantum cascade lasers with single phonon-continuum depopulation structures,” IEEE J. Quantum Electron. 46, 683–688 (2010). [CrossRef]

]. The layered structure was grown by metal organic vapour-phase epitaxy and the laser chip was mounted epi-side-down on a heat sink.

3. Measurements

Fig. 2 a) Comparison between the FNPSDs of a cryogenic QCL (light gray, QCL2, operating current Io 2 = 219 mA) and the RT QCL studied in this work (dark gray, QCL1, operating current Io 1 = 776 mA). The level of the flicker noise is about 200 times lower for the RT device. The plot also shows how the contribution from the current noise of our home-made driver, that was negligible for the cryogenic QCL, now becomes relevant. b) The same measurement is repeated with the commercial current driver. Despite the larger noise contribution below 10 MHz, the strong filtering at higher frequencies allows a clear observation of the white intrinsic noise. The dashed blue line, showing the 1/f trend, is the same for both graphs.

The situation is slightly different when the commercial current driver is used (see Fig. 2b). Here, the larger contribution from the current noise is even more dominant below 10 MHz, and prevents any useful interpretation. However, above 10 MHz, the commercial driver current noise drastically drops down, allowing a clean measurement of the QCL FNPSD, in agreement with what is measured with the home-made driver. A zoom of this last portion of both spectra is shown in Fig.3: the flattening of the FNPSD down to a white-noise level (Nw) is evident, and yields an intrinsic linewidth δνexp = πNw = 260±90 Hz, about four times smaller than that measured for the cryogenic QCL at the same value of Io/Ith (1.15). The uncertainty is calculated by taking into account both the scattering of the data in a single trace and the slope calibration error.

Fig. 3 The plot shows in detail the high-frequency portion of the measured FNPSD, where a flattening down to a white-noise level of 84 Hz2/Hz occurs. The sensitivity of our system is also represented by the detector noise level.

4. Discussion

A second interesting finding is obtained from the comparison between the measurements on RT and cryogenic QCLs: the intrinsic linewidth is larger at lower temperatures. A definitive test would be measuring the linewidth of QCL1 at different heat-sink temperatures (for example 300 K and 80 K). Unfortunately, we have not been able to perform this experiment yet, because the QCL case does not fit our cryostat. Nevertheless, the theoretical model just used for predicting the values of the intrinsic linewidth can also be applied for predicting its dependence on temperature. In order to do this, we figure out the expected temperature-dependence of the intrinsic linewidth of QCL1 in which, due to the temperature change, the pitch of the DFB grating is virtually tuned to match the lasing wavelength with peak-gain wavelength, thus keeping αe ∼ 0. The ratio of the relaxation times at the two different temperatures is estimated to be τ 3(300 K)/τ 3(80 K)≃0.6 (a relatively small change even for such a large temperature change, because of the presence of alloy disorder scatterings). The coupling efficiency β is inversely proportional to the spectral width ws of spontaneous emission, since this is the only temperature-dependent term involved in β (see equation (A14) of Ref. [4

4. M. Yamanishi, T. Edamura, K. Fujita, N. Akikusa, and H. Kan, “Theory of the intrinsic linewidth of quantum-cascade lasers: hidden reason for the narrow linewidth and line-broadening by thermal photons,” IEEE J. Quantum Electron. 44, 12–29 (2008). [CrossRef]

]). From the experimental result of the spectral width of the present device we obtain the ratio of the coupling efficiencies β (300 K)/β (80 K)= ws(80 K)/ws(300 K)≃ 0.5. On the other hand, the spontaneous emission lifetime τr and the photon decay rate γ are independent of temperature variations, as well as the small correction factor ɛ ≃ 0.2. Consequently, for I 0/Ith ≃ 1.15, the ratio of the intrinsic linewidths (∝ β (τ 3/τr)γ) is predicted to be δν(300 K)/δν(80 K)≃ 0.3. This can be considered a first theoretical confirmation of the dependence of the intrinsic linewidth on the operating temperature. Finally, we want to remark that the Schawlow-Townes-Henry formula [3

3. C. Henry, “Theory of the linewidth of semiconductor lasers,” IEEE J. Quantum Electron. 18, 259–264 (1982). [CrossRef]

] does not allow to evaluate the temperature dependence of the intrinsic linewidth.

Besides the comments on the intrinsic linewidth, the comparison between the low-frequency portion of QCL1 and QCL2 FNPSDs deserves further comments. The most relevant fact needing an explanation is the drastic reduction (δ f 2/δ f 1)2 ∼ 200 of the 1/f –type frequency noise for the RT QCL (QCL1). In Ref. [6

6. S. Borri, S. Bartalini, P. Cancio, I. Galli, G. Giusfredi, D. Mazzotti, M. Yamanishi, and P. De Natale, “Frequency-noise dynamics of mid-infrared quantum cascade lasers,” IEEE J. Quantum Electron. 47, 984–988 (2011). [CrossRef]

], some experimental evidences were given to support the hypothesis that the flicker frequency noise originates from temperature fluctuations induced by an internal tunnelling-current flicker noise δ I: δ fδ TRthermδ PRthermδ I. As a consequence, the frequency noise reduction is given by:
(δf2δf1)2(Rtherm2Rtherm1)2×(δI2δI1)2
(3)
Hence, a comparison between the thermal resistances and the flicker current noise of the RT and the cryogenic devices could help in identifying the origin of the large difference between the 1/f-type frequency noise of QCL1 and QCL2. This is further validated by the fact that all other key parameters involved in the comparison, such as injection barrier thickness, number of periods, thickness of one period and interface density are only sligthly different between the two devices (respectively 3.5 nm, 25, 51.7 nm and 425.53 μm−1 for QCL1 [9

9. K. Fujita, T. Edamura, N. Akikusa, A. Sugiyama, T. Ochiai, S. Furuta, A. Ito, M. Yamanishi, and H. Kan, “Quantum cascade lasers based on single phonon-continuum depopulation structures,” Proc. SPIE 7230, 723016 (2009). [CrossRef]

] and 4.6 nm, 22, 57.7 nm and ∼ 390 μm−1 for double-phonon design [16

16. D. Hofstetter, M. Beck, T. Aellen, and J. Faist, “High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm,” Appl. Phys. Lett. 78, 396–398 (2001). [CrossRef]

] QCL2 with a ∼ 11 μm bare ridge waveguide, a shorter cavity length of 1.5 mm, a comparable injector doping density of ∼ 3 × 1011 cm−2 and epi-side-up mounting; see Refs. [17

17. M. S. Vitiello, T. Gresch, A. Lops, V. Spagnolo, G. Scamarcio, N. Hoyler, M. Giovannini, and J. Faist, “Influence of InAs, AlAs δ layers on the optical, electronic, and thermal characteristics of strain-compensated GaInAs/AlInAs quantum-cascade lasers,” Appl. Phys. Lett. 91, 161111 (2007). [CrossRef]

, 18

18. M. S. Vitiello, G. Scamarcio, and V. Spagnolo, “Temperature dependence of thermal conductivity and boundary resistance in THz quantum cascade lasers,” IEEE J. Select Top. Quantum Electron. 14, 431–435 (2008). [CrossRef]

] for the definition of the interface density). On the contrary, by considering the temperature-dependent cross-plane thermal resistivity [19

19. M. S. Vitiello, V. Spagnolo, G. Scamarcio, A. Lops, Q. Yang, C. Manz, and J. Wagner, “Experimental investigation of the lattice and electronic temperatures in Ga0.47In0.53As/Al0.62Ga0.38As1xSbx quantum-cascade lasers,” Appl. Phys. Lett. 90, 121109 (2007). [CrossRef]

], and scaling for the different device length, the mounting geometry (epi-side up or down) and the active region temperature, the thermal resistance Rtherm 2 of QCL2 is convincingly inferred to be about 6 times higher than that of QCL1: Rtherm 2 ∼ 6Rtherm 1 ∼ 44.5 K/W. This higher thermal resistance well explains the observed thermal cut-off at 200 kHz for QCL2, as shown in Fig. 2(a) and also in Ref. [6

6. S. Borri, S. Bartalini, P. Cancio, I. Galli, G. Giusfredi, D. Mazzotti, M. Yamanishi, and P. De Natale, “Frequency-noise dynamics of mid-infrared quantum cascade lasers,” IEEE J. Quantum Electron. 47, 984–988 (2011). [CrossRef]

], though the thermal cut-off for QCL1, expected at around 1 MHz, is unfortunately masked by spurious noise. However the scaling of thermal resistance can only partially explain the huge reduction of the flicker FNPSD of Eq. 3 (a factor 36 vs. 200). An additional effect involving the internal current squared fluctuations δ I 2 must be assumed for explaining the remaining factor 200/36 ≃ 5.5. Switching from current to current-density squared fluctuations δ J 2 leads to an expected reduction of (δ J 2/δ J 1)2 ≃ 22, since the active region dimensions only differ for a factor two in length. This behavior could eventually involve the alternate capture and emission of electrons at individual quantum sites (defect sites in case of homogeneous semiconductors) which is known to generate discrete switching in the device resistance and, consequently, current fluctuations. A single occurrence of this effect is referred to as a random telegraph signal (RTS), and the summation of many RTSs in structured devices like QCLs may result in 1/f noise. The emission and trapping rates are expected to be proportional to the exponential form exp(−Ea/kB T), which means that the rate drastically increases with temperature. Here, the experimental results suggest the following hypothesis: at higher rates the contributions of individual RTSs may cancel out more effectively, resulting in a lower 1/f noise. Basing on these considerations we assume, for the squared current-density flicker noise, an inverse exponential form δ J 2 ∝ 1/exp(−2Ea/kB T). Consequently, the factor 22 in the ratio of squared current-density fluctuations (δ J 2/δ J 1)2 = exp(2Ea/kB T 2)/exp(2Ea/kB T 1) leads to an empirical estimation of the activation energy Ea ∼ 50 meV, which is comparable to thermal energies in the considered temperature range. A deeper investigation is required in order to give a more reliable and quantitative treatment. Nevertheless, the discussion presented above adds valuable elements supporting the correlation between internal current fluctuations and flicker fluctuations in the electron populations of the QCL quantum structure.

Finally, we want to discuss some perspectives concerning linewidth reduction of our RT QCL, based on the experimental data shown above. First, we must conclude that a further improvement of the laser driver current noise is required in order to fully exploit the drastic reduction of the QCL frequency noise. The noise level, currently in the range of 1–2 nA/ Hz, needs to be lowered down of at least one order of magnitude. Alternatively, a low-pass filtering on the current output should be implemented, at the expense of the modulation bandwidth of the driver. In this frame, it is possible to implement a frequency-locking loop acting on the driving current for a reduction of the laser linewidth. Following Ref. [5

5. D. S. Elliott, R. Roy, and S. J. Smith, “Extracavity laser band-shape and bandwidth modification,” Phys. Rev. A 26, 12–18 (1982). [CrossRef]

], from the experimental FNPSD of the RT QCL we calculate a free-running linewidth of about 400 kHz (FWHM) over an observation time of 10 ms. This is not a suitable linewidth for demanding spectroscopic experiments in the mid-infrared range. As an example, the present broad free-running linewidth of our QCL limits its application to the case of ultra-high-sensitivity Saturated-Absorption Cavity-Ring-down spectroscopy (see Ref. [20

20. G. Giusfredi, S. Bartalini, S. Borri, P. Cancio, I. Galli, D. Mazzotti, and P. De Natale, “Saturated-absorption cavity ring-down spectroscopy,” Phys. Rev. Lett. 104, 110801 (2010). [CrossRef] [PubMed]

]), since it requires laser radiation coupling to a high-finesse cavity mode with a few kHz width. Indeed, mid-IR QCLs can be combined with well-established techniques [21

21. S. Bartalini, S. Borri, and P. De Natale, “Doppler-free polarization spectroscopy with a quantum cascade laser at 4.3 μm,” Opt. Express 17, 7440–7449 (2009). [CrossRef] [PubMed]

] to efficiently narrow their linewidth even below the intrinsic levels, as demonstrated in a pioneering work by Taubman et al. [22

22. M. S. Taubman, T. L. Myers, B. D. Cannon, R. M. Williams, F. Capasso, C. Gmachl, D. L. Sivco, and A. Y. Cho , “Frequency stabilization of quantum cascade lasers by use of optical cavities” Opt. Lett. 27, 2164–2166 (2002). [CrossRef]

]. Following the recent work by Di Domenico et al. [23

23. G. Di Domenico, S. Schilt, and P. Thomann, “Simple approach to the relation between laser frequency noise and laser line shape,” Appl. Opt. 49, 4801–4807 (2010). [CrossRef] [PubMed]

], we can conclude that with moderate bandwidth (less than 100 kHz) and gain (about 50 dB at 10 Hz) a narrowing of the QCL source down to the kHz level can be easily achieved. Comparable narrowing of the cryogenic QCL would clearly require a larger servo loop bandwidth, given its measured FNPSD.

5. Conclusions

Acknowledgments

We gratefully acknowledge Dr. Pablo Cancio Pastor for his critical reading of the manuscript and M. Giuntini, A. Montori and M. De Pas from LENS for their help on driving electronics. This work was partially supported by Ente Cassa di Risparmio di Firenze and by Regione Toscana through the projects CTOTUS and SIMPAS, in the framework of POR–CReO FESR 2007–2013.

References and links

1.

S. Bartalini, S. Borri, P. Cancio, A. Castrillo, I. Galli, G. Giusfredi, D. Mazzotti, L. Gianfrani, and P. De Natale, “Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow–Townes limit,” Phys. Rev. Lett. 104, 083904 (2010). [CrossRef] [PubMed]

2.

J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, and A. Y. Cho, “Quantum cascade laser,” Science264, 553–556 (1994). [CrossRef] [PubMed]

3.

C. Henry, “Theory of the linewidth of semiconductor lasers,” IEEE J. Quantum Electron. 18, 259–264 (1982). [CrossRef]

4.

M. Yamanishi, T. Edamura, K. Fujita, N. Akikusa, and H. Kan, “Theory of the intrinsic linewidth of quantum-cascade lasers: hidden reason for the narrow linewidth and line-broadening by thermal photons,” IEEE J. Quantum Electron. 44, 12–29 (2008). [CrossRef]

5.

D. S. Elliott, R. Roy, and S. J. Smith, “Extracavity laser band-shape and bandwidth modification,” Phys. Rev. A 26, 12–18 (1982). [CrossRef]

6.

S. Borri, S. Bartalini, P. Cancio, I. Galli, G. Giusfredi, D. Mazzotti, M. Yamanishi, and P. De Natale, “Frequency-noise dynamics of mid-infrared quantum cascade lasers,” IEEE J. Quantum Electron. 47, 984–988 (2011). [CrossRef]

7.

R. M. Williams, J. F. Kelly, J. S. Hartman, S. W. Sharpe, M. S. Taubman, J. L. Hall, F. Capasso, C. Gmachl, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho, “Kilohertz linewidth from frequency-stabilized mid-infrared quantum cascade lasers,” Opt. Lett. 24, 1844–1846 (1999). [CrossRef]

8.

T. L. Myers, R. M. Williams, M. S. Taubman, C. Gmachl, F. Capasso, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho, “Free-running frequency stability of mid-infrared quantum cascade lasers,” Opt. Lett. 27, 170–172 (2002). [CrossRef]

9.

K. Fujita, T. Edamura, N. Akikusa, A. Sugiyama, T. Ochiai, S. Furuta, A. Ito, M. Yamanishi, and H. Kan, “Quantum cascade lasers based on single phonon-continuum depopulation structures,” Proc. SPIE 7230, 723016 (2009). [CrossRef]

10.

K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “Room temperature, continuous-wave operation of quantum cascade lasers with single phonon resonance-continuum depopulation structures grown by metal organic vapor-phase epitaxy,” Appl. Phys. Lett. 91, 141121 (2007). [CrossRef]

11.

K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “High-performance λ ∼ 8.6 μm quantum cascade lasers with single phonon-continuum depopulation structures,” IEEE J. Quantum Electron. 46, 683–688 (2010). [CrossRef]

12.

K. G. Libbrecht and J. L. Hall, “A low-noise high-speed diode laser current controller,” Rev. Sci. Instrum. 64, 2133–2135 (1993). [CrossRef]

13.

J. S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi, “High-power continuous-wave operation of a 6 μm quantum-cascade laser at room temperature,” Appl. Phys. Lett. 83, 2503–2505 (2003). [CrossRef]

14.

A. Vasanelli, A. Leuliet, C. Sirtori, A. Wade, G. Fedorov, D. Smirnov, G. Bastard, B. Vinter, M. Giovannini, and J. Faist, “Role of elastic scattering mechanisms in GaInAs/AlInAs quantum cascade lasers,” Appl. Phys. Lett. , 89, 172120 (2006). [CrossRef]

15.

K. Fujita, M. Yamanishi, T. Edamura, A. Sugiyama, and S. Furuta, “Extremely high T0-values (≃450 K) of long-wavelength (≃ 15 μm), low-threshold-current-density quantum-cascade lasers based on the indirect pump scheme,” Appl. Phys. Lett. 97, 201109 (2010).

16.

D. Hofstetter, M. Beck, T. Aellen, and J. Faist, “High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 μm,” Appl. Phys. Lett. 78, 396–398 (2001). [CrossRef]

17.

M. S. Vitiello, T. Gresch, A. Lops, V. Spagnolo, G. Scamarcio, N. Hoyler, M. Giovannini, and J. Faist, “Influence of InAs, AlAs δ layers on the optical, electronic, and thermal characteristics of strain-compensated GaInAs/AlInAs quantum-cascade lasers,” Appl. Phys. Lett. 91, 161111 (2007). [CrossRef]

18.

M. S. Vitiello, G. Scamarcio, and V. Spagnolo, “Temperature dependence of thermal conductivity and boundary resistance in THz quantum cascade lasers,” IEEE J. Select Top. Quantum Electron. 14, 431–435 (2008). [CrossRef]

19.

M. S. Vitiello, V. Spagnolo, G. Scamarcio, A. Lops, Q. Yang, C. Manz, and J. Wagner, “Experimental investigation of the lattice and electronic temperatures in Ga0.47In0.53As/Al0.62Ga0.38As1xSbx quantum-cascade lasers,” Appl. Phys. Lett. 90, 121109 (2007). [CrossRef]

20.

G. Giusfredi, S. Bartalini, S. Borri, P. Cancio, I. Galli, D. Mazzotti, and P. De Natale, “Saturated-absorption cavity ring-down spectroscopy,” Phys. Rev. Lett. 104, 110801 (2010). [CrossRef] [PubMed]

21.

S. Bartalini, S. Borri, and P. De Natale, “Doppler-free polarization spectroscopy with a quantum cascade laser at 4.3 μm,” Opt. Express 17, 7440–7449 (2009). [CrossRef] [PubMed]

22.

M. S. Taubman, T. L. Myers, B. D. Cannon, R. M. Williams, F. Capasso, C. Gmachl, D. L. Sivco, and A. Y. Cho , “Frequency stabilization of quantum cascade lasers by use of optical cavities” Opt. Lett. 27, 2164–2166 (2002). [CrossRef]

23.

G. Di Domenico, S. Schilt, and P. Thomann, “Simple approach to the relation between laser frequency noise and laser line shape,” Appl. Opt. 49, 4801–4807 (2010). [CrossRef] [PubMed]

OCIS Codes
(270.2500) Quantum optics : Fluctuations, relaxations, and noise
(290.3700) Scattering : Linewidth
(140.3425) Lasers and laser optics : Laser stabilization
(140.5965) Lasers and laser optics : Semiconductor lasers, quantum cascade

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: August 3, 2011
Revised Manuscript: August 18, 2011
Manuscript Accepted: August 19, 2011
Published: August 29, 2011

Citation
S. Bartalini, S. Borri, I. Galli, G. Giusfredi, D. Mazzotti, T. Edamura, N. Akikusa, M. Yamanishi, and P. De Natale, "Measuring frequency noise and intrinsic linewidth of a room-temperature DFB quantum cascade laser," Opt. Express 19, 17996-18003 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-19-17996


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References

  1. S. Bartalini, S. Borri, P. Cancio, A. Castrillo, I. Galli, G. Giusfredi, D. Mazzotti, L. Gianfrani, and P. De Natale, “Observing the intrinsic linewidth of a quantum-cascade laser: beyond the Schawlow–Townes limit,” Phys. Rev. Lett.104, 083904 (2010). [CrossRef] [PubMed]
  2. J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, and A. Y. Cho, “Quantum cascade laser,” Science264, 553–556 (1994). [CrossRef] [PubMed]
  3. C. Henry, “Theory of the linewidth of semiconductor lasers,” IEEE J. Quantum Electron.18, 259–264 (1982). [CrossRef]
  4. M. Yamanishi, T. Edamura, K. Fujita, N. Akikusa, and H. Kan, “Theory of the intrinsic linewidth of quantum-cascade lasers: hidden reason for the narrow linewidth and line-broadening by thermal photons,” IEEE J. Quantum Electron.44, 12–29 (2008). [CrossRef]
  5. D. S. Elliott, R. Roy, and S. J. Smith, “Extracavity laser band-shape and bandwidth modification,” Phys. Rev. A26, 12–18 (1982). [CrossRef]
  6. S. Borri, S. Bartalini, P. Cancio, I. Galli, G. Giusfredi, D. Mazzotti, M. Yamanishi, and P. De Natale, “Frequency-noise dynamics of mid-infrared quantum cascade lasers,” IEEE J. Quantum Electron.47, 984–988 (2011). [CrossRef]
  7. R. M. Williams, J. F. Kelly, J. S. Hartman, S. W. Sharpe, M. S. Taubman, J. L. Hall, F. Capasso, C. Gmachl, D. L. Sivco, J. N. Baillargeon, and A. Y. Cho, “Kilohertz linewidth from frequency-stabilized mid-infrared quantum cascade lasers,” Opt. Lett.24, 1844–1846 (1999). [CrossRef]
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