Frequency characterization of a swept- and fixed-wavelength external-cavity quantum cascade laser by use of a frequency comb

Knabe, Kevin; Williams, Paul; Giorgetta, Fabrizio R.; Armacost, Chris M.; Crivello, Sam; Radunsky, Michael B.; Newbury, Nathan R.

doi:10.1364/oe.20.012432

Cited by 27 publications

(27 citation statements)

References 19 publications

(40 reference statements)

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“…As a result of this significant electrical flicker noise, the use of an external cavity configuration did not lead to a narrower short-term linewidth [16] than typically encountered in DFB-QCLs. Therefore, the only way to achieve narrow-linewidth QCLs so far has been based on the use of some active noise reduction techniques, such as by frequency stabilization to an optical frequency reference (e.g., a molecular transition [17,18] or the reso-nance of a Fabry-Perot cavity using electronic [19] or opti-cal feedback [20]).…”

Section: Introductionmentioning

confidence: 87%

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

et al. 2015

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Section: Introductionmentioning

confidence: 87%

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

et al. 2015

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“…From 2 MHz for the free-running QCL, the linewidth is narrowed below 700 kHz (10 ms observatio The growing interest for high-resolution spectroscopy experiments has pushed scientists to investigate the ultimate limits that these devices can achieve in terms of frequency stability. Frequency noise and linewidth properties of free-running QCLs were investigated in various experimental setups in the mid-IR with distributed feedback (DFB) [4,5] and external cavity configurations [6], as well as in the terahertz domain [7]. Moreover, different active frequency-stabilization experiments for linewidth narrowing have been reported.…”

mentioning

confidence: 99%

Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference

Tombez¹,

Schilt²,

Hofstetter³

et al. 2013

Opt. Lett.

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We report on a technique for frequency noise reduction and linewidth-narrowing of a distributed-feedback mid-IR quantum cascade laser (QCL) that does not involve any optical frequency reference. The voltage fluctuations across the QCL are sensed, amplified and fed back to the temperature of the QCL at a fast rate using a near-IR laser illuminating the top of the QCL chip. A locking bandwidth of 300 kHz and a reduction of the frequency noise power spectral density by a factor of 10 with respect to the free-running laser are achieved. From 2 MHz for the free-running QCL, the linewidth is narrowed below 700 kHz (10 ms observatio The growing interest for high-resolution spectroscopy experiments has pushed scientists to investigate the ultimate limits that these devices can achieve in terms of frequency stability. Frequency noise and linewidth properties of free-running QCLs were investigated in various experimental setups in the mid-IR with distributed feedback (DFB) [4,5] and external cavity configurations [6], as well as in the terahertz domain [7]. Moreover, different active frequency-stabilization experiments for linewidth narrowing have been reported. Generally, a frequency-sensitive element is used to sense the fluctuations of the laser frequency and generate an error-signal that is usually fed back to the QCL injection current. Several methods were demonstrated using high-finesse optical cavities In this Letter, we present a different approach for frequency noise reduction and linewidth-narrowing of a 4.55 μm QCL that does not involve any optical frequency reference. Following the observation that frequency noise in DFB QCLs arises from electrical power fluctuations due to the electronic transport in the devices [13,14], in this work we assess and experimentally demonstrate linewidth narrowing using only the voltage fluctuations across the QCL as an error signal for a feedback loop. This error signal is generated without measuring the actual fluctuations of the QCL optical frequency. A similar approach aiming at using the voltage noise (VN) measured across a near-IR laser-diode in order to implement an electrical feedback to reduce the phase noise was proposed [15] but never demonstrated to the best of our knowledge. We show here a reduction of the frequency noise power spectral density (PSD) of one order of magnitude within the bandwidth of the feedback loop (>100 kHz).The laser used in our experiment is a 4.55 μm buriedheterostructure DFB QCL provided by Alpes Lasers. The stabilization scheme is shown in Fig. 1. The QCL is mounted on a Peltier-cooler operated at 20°C and an output power of 10 mW is obtained at an injection current of 260 mA (the threshold current is I th 220 mA). A lownoise current source is used to drive the QCL with a current noise lower than 1 nA∕ p Hz in order to avoid any linewidth broadening resulting from technical noise [16]. In these conditions, the contribution of the injection current noise to the frequency noise is negligible and the fluctuations of the QCL laser frequency are i...

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“…This makes them ideally suited for broadband absorption spectroscopy and for the simultaneous detection of multiple gases. On the other hand, their use for precision spectroscopy has been hampered so far by a large amount of frequency noise, resulting in an optical linewidth of about 30 MHz over 50 ms [1]. This is one of the reasons why neither their frequency nor their phase have been so far locked to a frequency comb.…”

mentioning

confidence: 99%

Frequency locking of an extended-cavity quantum cascade laser to a frequency comb for precision mid infrared spectroscopy

Alsaif

Lamperti

Gatti

et al. 2017

2017 Conference on Lasers and Electro-Optics Europe &Amp; European Quantum Electronics Conference (CLEO/Europe-EQEC)

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Extended-cavity quantum cascade lasers (EC-QCLs) enable mode-hope-free frequency sweeps in the midinfrared region over ranges in excess of 100 cm -1 , at speeds up to 1 THz/s and with a 100-mW optical power level. This makes them ideally suited for broadband absorption spectroscopy and for the simultaneous detection of multiple gases. On the other hand, their use for precision spectroscopy has been hampered so far by a large amount of frequency noise, resulting in an optical linewidth of about 30 MHz over 50 ms [1]. This is one of the reasons why neither their frequency nor their phase have been so far locked to a frequency comb. Their use in combination with frequency combs has been performed in an open loop regime only [2], which has the merit of preserving the inherently fast modulation speed of these lasers, yet not to afford high spectral resolution and accuracy.Here we report for the first time frequency locking of an EC-QCL to a frequency comb. The lock relies on an external frequency correction given by an acousto-optical frequency shifter (AOFS) in a feedback configuration, according to the experimental setup depicted in Fig. 1(a). An EC-QCL from Daylight Solutions with tunability in the 7.5-8.2 m range and emitting up to 100 mW is frequency shifted by an AOFS. It is arranged in a double pass configuration to maximize the frequency modulation depth while compensating for beam-steering effects due to the large laser-frequency jittering. The beat-note between the laser and a 100-MHz Tm:fiber frequency comb is obtained by heterodyning at around 1.57 m the supercontinuum light generated by the comb itself with the sumfrequency between EC-QCL and main 1.95-m comb output [3] generated in a ZGP crystal. The beat-note is stabilized with a double servo loop acting on the piezo-electric laser frequency actuator till 60 Hz and on the AOFS at higher frequencies. The power spectral density of the error signal used to stabilize the EC-QCL displayed in Fig. 1(b) shows significant laser noise suppression till 10 kHz. It was impossible in our current configuration to achieve a larger control bandwidth due to the s-level delay introduced in the loop by the AOFS. The loop was anyway sufficient to reduce by more than a factor of 10 the EC-QCL linewidth, as attested by the 2.5-MHz-large beat-note signal shown in the inset. Application of this stable comb-referenced source to spectroscopy is under way.

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Frequency characterization of a swept- and fixed-wavelength external-cavity quantum cascade laser by use of a frequency comb

Cited by 27 publications

References 19 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

Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference

Frequency locking of an extended-cavity quantum cascade laser to a frequency comb for precision mid infrared spectroscopy

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