Observing the Intrinsic Linewidth of a Quantum-Cascade Laser: Beyond the Schawlow-Townes Limit

Bartalini, S.; Borri, Simone; Cancio, P.; Castrillo, A.; Galli, Iacopo; Giusfredi, G.; Mazzotti, D.; Gianfrani, L.; Natale, P. De

doi:10.1103/physrevlett.104.083904

Cited by 153 publications

(119 citation statements)

References 20 publications

Supporting

Mentioning

113

Contrasting

Order By: Relevance

“…The QCLs frequency noise was measured using a spectroscopic setup as implemented in former studies [7,[10][11][12]. The side of a molecular transition was used as a frequency-to-intensity converter (a so-called frequency Here, a 10-cm-long sealed glass cell filled with 2 mbar of pure N 2 O was used with QCLs emitting in the 7.6-8 μm wavelength range.…”

Section: Methodsmentioning

confidence: 99%

“…Novel applications of QCLs in very high-resolution spectroscopy and optical metrology have emerged in the last years, in particular in combination with optical frequency combs [2][3][4][5], which are generally more demanding in terms of low frequency-noise and nar-row spectral linewidth. QCLs have the potential to achieve very narrow linewidths with an intrinsic value of a few hundreds hertz only [6,7] resulting from their close-to-zero Henry's linewidth enhancement factor [8]. However, a narrow linewidth is generally not achieved in practice in freerunning QCLs as a result of the presence of undesired noise that compromises their spectral properties.…”

Section: Introductionmentioning

confidence: 99%

“…Hence, the char-acterization and understanding of the origin of frequency noise spectrum of free-running QCLs gained a significant interest in the recent years. A few research groups reported experimental frequency noise spectra for QCLs produced by different manufacturers and operated at temperatures ranging from cryogenic [7,9] up to room temperature [6,10,11]. Significantly different levels of noise have been observed in the considered QCLs, leading to linewidths in the range of sub-100 kHz [6] to many megahertz [7].…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

An experimental study of noise in mid-infrared quantum cascade lasers of different designs

et al. 2015

View full text Add to dashboard Cite

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

An experimental study of noise in mid-infrared quantum cascade lasers of different designs

et al. 2015

View full text Add to dashboard Cite

“…2 shows the resulting frequency noise power spectral density (PSD) of the QCL. It has a 1/f trend at low frequency, followed by a steeper slope above ∼ 300 kHz, as observed in 21,22 . Note however that the measured frequency noise PSD is roughly one order of magnitude lower than previously published characterizations of free-running cw-mode near-RT DFB QCLs 20-24 .…”

mentioning

confidence: 72%

A widely tunable 10-μm quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy

Sow

Mejri

Tokunaga

et al. 2014

Applied Physics Letters

View full text Add to dashboard Cite

We report the coherent phase-locking of a quantum cascade laser (QCL) at 10-µm to the secondary frequency standard of this spectral region, a CO 2 laser stabilized on a saturated absorption line of OsO 4 . The stability and accuracy of the standard are transferred to the QCL resulting in a line width of the order of 10 Hz, and leading to our knowledge to the narrowest QCL to date. The locked QCL is then used to perform absorption spectroscopy spanning 6 GHz of NH 3 and methyltrioxorhenium, two species of interest for applications in precision measurements.With their rich internal structure, molecules can play a decisive role in precision tests of fundamental physics. They are being used to test fundamental symmetries such as parity 1-3 or parity and time reversal 4 , to measure absolute values of fundamental constants 5-7 and their possible temporal variation [8][9][10] . Many of these experiments can be cast as measurements of resonance frequencies of molecular transitions, for which ultra-stable and accurate sources in the mid-infrared (mid-IR) are highly desirable, since most rovibrational transitions are to be found in that region.Our group has a long-standing interest in performing spectroscopic precision measurements on molecules at extreme resolutions around 10 µm 1,9,11 . We are currently working on two such measurements: the determination of the Boltzmann constant, k B , by Doppler spectroscopy of ammonia 6,12 and the first observation of parity violation by Ramsey interferometry of a beam of chiral molecules 3,13 . For these experiments, we currently use spectrometers based on custom built ultra-stable CO 2 lasers. We obtain the required metrological frequency stability and accuracy -10 Hz line width, 1 Hz stability at 1 s, accuracy of a few tens of hertz 14,15 -by stabilizing these lasers to saturated absorption lines of molecules such as OsO 4 . CO 2 lasers have a major shortcoming: a lack of tunability. They emit at CO 2 molecular resonances. An emission line is found every 30 to 50 GHz in the 9-11 µm wavelength range, and each line is tunable over about 100 MHz. Although, as in our spectrometers, this range can be extended a few gigahertz using electrooptical modulators (EOMs), this is done at the expense of power (EOMs at these wavelengths have an efficiency of 10 −4 ) and necessitates subsequent spectral filtering. Overcoming these difficulties without the loss of stability is key to enabling precision measurements in the mid-IR.One solution would be to use frequency combreferenced continuous-wave (cw) [16][17][18] or femtosecond mid-IR sources. These are based on frequency mixing in nonlinear crystals and provide absolute-frequency referencing, reasonable line widths and tunability, but are very complex and often exhibit limited power. By comparison, cw quantum cascade lasers (QCLs) are a new mature and robust technology that offer broad and continuous tuning over several hundred gigahertz at 100 mW-level powers. Several can be combined giving access to the whole mid-IR region. Recent studies of...

show abstract

“…Optical frequency discriminators directly convert optical frequency fluctuations of the laser into intensity fluctuations that are detected by a photodetector. Optical discriminators are typically devices displaying a frequency-dependent transmission in a restricted frequency range, such as gas-filled cells near an atomic/molecular resonance (Doppler-broadened [10][11][12] or sub-Doppler 13 ), Fabry-Perot resonators 14 or unbalanced twobeam interferometers. 15 As it is not always possible to have a proper optical discriminator at the considered laser wavelength, another approach consists in heterodyning the laser under test with a second laser, either similar to the first one or with a negligible frequency noise, and subsequently analyzing the generated RF beat signal.…”

Section: Frequency Discriminatorsmentioning

confidence: 99%

Frequency discriminators for the characterization of narrow-spectrum heterodyne beat signals: Application to the measurement of a sub-hertz carrier-envelope-offset beat in an optical frequency comb

Schilt

Bucalović

Tombez

et al. 2011

Review of Scientific Instruments

View full text Add to dashboard Cite

We describe a radio-frequency (RF) discriminator, or frequency-to-voltage converter, based on a voltage-controlled oscillator phase-locked to the signal under test, which has been developed to analyze the frequency noise properties of an RF signal, e.g., a heterodyne optical beat signal between two lasers or between a laser and an optical frequency comb. We present a detailed characterization of the properties of this discriminator and we compare it to three other commercially available discriminators. Owing to its large linear frequency range of 7 MHz, its bandwidth of 200 kHz and its noise floor below 0.01 Hz 2 /Hz in a significant part of the spectrum, our frequency discriminator is able to fully characterize the frequency noise of a beat signal with a linewidth ranging from a couple of megahertz down to a few hertz. As an example of application, we present measurements of the frequency noise of the carrier envelope offset beat in a low-noise optical frequency comb.

show abstract

Observing the Intrinsic Linewidth of a Quantum-Cascade Laser: Beyond the Schawlow-Townes Limit

Cited by 153 publications

References 20 publications

An experimental study of noise in mid-infrared quantum cascade lasers of different designs

An experimental study of noise in mid-infrared quantum cascade lasers of different designs

A widely tunable 10-μm quantum cascade laser phase-locked to a state-of-the-art mid-infrared reference for precision molecular spectroscopy

Frequency discriminators for the characterization of narrow-spectrum heterodyne beat signals: Application to the measurement of a sub-hertz carrier-envelope-offset beat in an optical frequency comb

Contact Info

Product

Resources

About