## Measuring frequency noise and intrinsic linewidth of a room-temperature DFB quantum cascade laser |

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 *μ*m 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

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]

*μ*m and we compare it with the same quantity already measured for a cryogenic QCL at 4.33

*μ*m. 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

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]

*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.

^{0}1–00

^{0}0) P(56) line of CO

_{2}, 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/

^{2}/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]

_{2}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

*I*= 674 mA, while the molecular resonance is found at an operating current

_{th}*I*= 776 mA, giving a ratio

_{o}*I*/

_{o}*I*= 1.15. In these conditions, the laser output power is about 20 mW.

_{th}_{0.72}Ga

_{0.28}As/In

_{0.31}Al

_{0.69}As 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]

*μ*m bare ridge, 3 mm length, and an injector doping density of ∼ 2 × 10

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

## 3. Measurements

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]

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]

*f*behavior, the ratio between the two noise spectra is constant at about 200. In the 10–200 kHz range, the noise contribution from the current driver is dominant and hinders precise measurement of the QCL frequency noise. This was not observed with the cryogenic QCL, due to its larger FNPSD. Between 1 MHz and 10 MHz the RT QCL shows a noise feature not originating from the current noise and resulting from an envelope of adjacent spikes. We think that this technical noise could arise from a non-optimized electrical grounding of the RT QCL. Finally, above 10 MHz, both the current noise of the home-made driver and the technical noise are negligible, allowing the pure QCL frequency noise to emerge. Despite the spurious contributions described above, we can state that all the FNPSD of the QCL (before the white-noise flattening) is consistent with an 1/

*f*behavior.

*N*) is evident, and yields an intrinsic linewidth

_{w}*δν*=

_{exp}*πN*= 260±90 Hz, about four times smaller than that measured for the cryogenic QCL at the same value of

_{w}*I*/

_{o}*I*(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.

_{th}## 4. Discussion

**104**, 083904 (2010). [CrossRef] [PubMed]

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]

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]

_{1}, and to the cryogenic QCL used in our previous work [1

**104**, 083904 (2010). [CrossRef] [PubMed]

_{2}. Due to the CW-operation, all the parameters must be calculated at active region temperatures. At threshold,

*I*= 674 mA for QCL

_{th}_{1}, the active region temperature is determined to be the temperature giving, in pulsed operation, the same threshold current as in CW-operation, namely ∼ 340 K, about 50 K higher than the heat-sink temperature

*T*∼290 K (see Ref. [13

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

_{1}, it results an active region temperature

*T*

_{1}∼350 K at the bias conditions

*I*

_{0}= 776 mA and

*V*= 10 V (with a thermal resistance

_{bias}*R*

_{therm}_{1}∼ 7.42 K/W). With a different manner, the active region temperature of QCL

_{2}(at its experimental bias conditions

*I*

_{0}= 219 mA and

*V*= 10 V) is

_{bias}*T*

_{2}∼ 182 K, about 97 K higher than the heat-sink temperature

*T*= 85 K (see discussion for the higher thermal resistance

*R*

_{therm}_{2}∼ 44.5 K/W of QCL

_{2}, below Eq. 3).

_{1}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 QCL

_{1}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

*α*∼ 0. The ratio of the relaxation times at the two different temperatures is estimated to be

_{e}*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

*w*of spontaneous emission, since this is the only temperature-dependent term involved in

_{s}*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]

*β*(300 K)/

*β*(80 K)=

*w*(80 K)/

_{s}*w*(300 K)≃ 0.5. On the other hand, the spontaneous emission lifetime

_{s}*τ*and the photon decay rate

_{r}*γ*are independent of temperature variations, as well as the small correction factor

*ɛ*≃ 0.2. Consequently, for

*I*

_{0}/

*I*≃ 1.15, the ratio of the intrinsic linewidths (∝

_{th}*β*(

*τ*

_{3}/

*τ*)

_{r}*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]

_{1}and QCL

_{2}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 (QCL

_{1}). 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]

*δ I*:

*δ f*∝

*δ T*∼

*R*∝

_{therm}δ P*R*. As a consequence, the frequency noise reduction is given by: 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/

_{therm}δ I*f*-type frequency noise of QCL

_{1}and QCL

_{2}. 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

*μ*m

^{−1}for QCL

_{1}[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]

*μ*m

^{−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 *μ*m,” Appl. Phys. Lett. **78**, 396–398 (2001). [CrossRef]

_{2}with a ∼ 11

*μ*m bare ridge waveguide, a shorter cavity length of 1.5 mm, a comparable injector doping density of ∼ 3 × 10

^{11}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. 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 Ga_{0.47}In_{0.53}As/Al_{0.62}Ga_{0.38}As_{1}_{–}* _{x}*Sb

*quantum-cascade lasers,” Appl. Phys. Lett.*

_{x}**90**, 121109 (2007). [CrossRef]

*R*

_{therm}_{2}of QCL

_{2}is convincingly inferred to be about 6 times higher than that of QCL

_{1}:

*R*

_{therm}_{2}∼ 6

*R*

_{therm}_{1}∼ 44.5 K/W. This higher thermal resistance well explains the observed thermal cut-off at 200 kHz for QCL

_{2}, 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]

_{1}, 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(−

*E*/

_{a}*k*

_{B}*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(−2

*E*/

_{a}*k*

_{B}*T*). Consequently, the factor 22 in the ratio of squared current-density fluctuations (

*δ*

*J*

_{2}/

*δ*

*J*

_{1})

^{2}= exp(2

*E*/

_{a}*k*

_{B}*T*

_{2})/exp(2

*E*/

_{a}*k*

_{B}*T*

_{1}) leads to an empirical estimation of the activation energy

*E*∼ 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.

_{a}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]

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 *μ*m,” 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]

## 5. Conclusions

*μ*m is completely characterized. An intrinsic linewidth of 260 Hz, about four times smaller than in a cryogenic QCL, is measured, in reasonable agreement with the theoretical value. The flicker 1/

*f*–type frequency noise, occurring at lower frequencies, is also drastically reduced (about a factor 200) with respect to the case of a cryogenically-operated QCL at the same wavelength. A physical interpretation of the measured behaviour is proposed, based on the hypothesis that the flicker frequency noise originates from temperature fluctuations induced by an internal tunnelling-current flicker noise. The temperature dependence of both the thermal resistance and the current flicker noise well explains the experimental results, assigning a predominant effect of the heterostructure in determining the shape and amplitude of the FNPSD curve. In conclusion, if an important element for the success of QCLs has undoubtedly been the tailoring of their emitted frequency, we believe that tailoring of QCLs spectral features is now possible and it can be the key for their next most demanding applications.

## Acknowledgments

## 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. |

2. | J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, and A. Y. Cho, “Quantum cascade laser,” |

3. | C. Henry, “Theory of the linewidth of semiconductor lasers,” IEEE J. Quantum Electron. |

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. |

5. | D. S. Elliott, R. Roy, and S. J. Smith, “Extracavity laser band-shape and bandwidth modification,” Phys. Rev. A |

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. |

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. |

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. |

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 |

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. |

11. | K. Fujita, S. Furuta, A. Sugiyama, T. Ochiai, T. Edamura, N. Akikusa, M. Yamanishi, and H. Kan, “High-performance |

12. | K. G. Libbrecht and J. L. Hall, “A low-noise high-speed diode laser current controller,” Rev. Sci. Instrum. |

13. | J. S. Yu, S. Slivken, A. Evans, L. Doris, and M. Razeghi, “High-power continuous-wave operation of a 6 |

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. , |

15. | K. Fujita, M. Yamanishi, T. Edamura, A. Sugiyama, and S. Furuta, “Extremely high |

16. | D. Hofstetter, M. Beck, T. Aellen, and J. Faist, “High-temperature operation of distributed feedback quantum-cascade lasers at 5.3 |

17. | M. S. Vitiello, T. Gresch, A. Lops, V. Spagnolo, G. Scamarcio, N. Hoyler, M. Giovannini, and J. Faist, “Influence of InAs, AlAs |

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. |

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 Ga quantum-cascade lasers,” Appl. Phys. Lett. _{x}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. |

21. | S. Bartalini, S. Borri, and P. De Natale, “Doppler-free polarization spectroscopy with a quantum cascade laser at 4.3 |

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. |

23. | G. Di Domenico, S. Schilt, and P. Thomann, “Simple approach to the relation between laser frequency noise and laser line shape,” Appl. Opt. |

**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

- 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]
- 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]
- C. Henry, “Theory of the linewidth of semiconductor lasers,” IEEE J. Quantum Electron.18, 259–264 (1982). [CrossRef]
- 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]
- D. S. Elliott, R. Roy, and S. J. Smith, “Extracavity laser band-shape and bandwidth modification,” Phys. Rev. A26, 12–18 (1982). [CrossRef]
- 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]
- 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]
- 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]
- 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. SPIE7230, 723016 (2009). [CrossRef]
- 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]
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