Kilohertz Linewidth Research Articles

1018 nm High-Power Tunable Single-Frequency VECSEL With Kilohertz Linewidth

1018 nm High-Power Tunable Single-Frequency VECSEL With Kilohertz Linewidth

Carrier-resolved real-field theory of multi-octave frequency combs

Optical frequency combs are pillars of precision spectroscopy, and their microresonator realization serves applications where miniaturization and large tooth separation are important. Microresonator combs cover an enormous range of time scales varying from the femtosecond periods of optical oscillations to milliseconds corresponding to the kilohertz linewidth of the comb teeth. Here, we develop and implement the carrier-resolved real-field model for multi-octave frequency combs, which allows for nearly ab initio capture of all the time scales involved. As an example, we consider a microresonator that has a mix of second- and third-order nonlinearities and uses periodic poling. By applying the real-field approach, we demonstrate how to surpass traditional limitations and model the spectral broadening and soliton mode-locking across three optical octaves.

A robust Freeman-Hill-inspired pulse protocol for ringdown-free T1 relaxation measurements

A new difference-spectroscopy method is introduced for measuring T1 relaxation times. It is inspired by the earlier work of Freeman and Hill and eliminates the need for recording signal intensities at thermodynamic equilibrium. The new method is termed SIP-R (Split-Inversion Pulse and Recovery) and reduces the number of refinable parameters in the curve fitting process of relaxation-delay-dependent signal intensities by using two instead of the three parameters typically used in the standard inversion-recovery sequence. The SIP-R method preserves the dynamic range of measurement of the standard inversion-recovery method but converts the rise-to-maximum mathematical functionality of the recorded data into a decay-to-zero functionality. The decay-to-zero functionality renders the SIP-R sequence advantageous for inverse Laplace transformation numerical optimizations. The new technique proves to be extremely robust with respect to pulse imperfections, pulse-power changes during the pulse sequence, pulse-width miscalibrations, resonance offsets, and radiofrequency field variations. It also compensates for acoustic ring-down effects and proves reliable for measurements with inhomogeneously broadened signals up to several kilohertz linewidth. 1H NMR experiments with methane gas at pressures up to 50 atm in toroid-cavity pressure vessel probes and in the presence of the methane-to-methanol conversion catalyst Cu-ZnO/Al2O3 are used to show the usefulness of the new method for relaxation time investigations under pressure, at strong radiofrequency field gradients, and in the presence of paramagnetic materials.

4.4 W, Continuous-Wave, Narrow Linewidth Optical Parametric Oscillator at $3.77~\mu$ m

A high-power, continuous-wave, narrow linewidth singly resonant optical parametric oscillator at $3.77~ {\mu } \text{m}$ is demonstrated, which is pumped by a 1064 nm fiber laser featuring kilohertz linewidth. A moderate cavity finesse of the optical parametric oscillator at signal wavelength is applied, aiming at narrow linewidth signal and idler output. By optimizing the confocal parameter of the resonated signal wave, with a pump power of 34 W, mid-infrared idler wave with an output power of 4.4 W, and a minimum power fluctuation root mean square of 0.72 % is obtained. A linewidth of less than 25 MHz for the idler wave at $3.77~ {\mu } \text{m}$ was confirmed by checking the signal wave’s reflected interference pattern on an F-P cavity. At the maximum idler output, the M2 factors on the X and Y axis were 1.36 and 1.40, respectively.

Linearly Polarized Multi-Wavelength Fiber Laser Comb via Brillouin Random Lasing Oscillation

A linearly polarized multi-wavelength Brillouin laser comb in the 1.5- $\mu \text{m}$ telecom spectral window is established by cascading multiple Brillouin random lasing oscillations in a semi-open polarization maintaining fiber (PMF)-based composite cavity. Distributed Rayleigh scattering offers a broadband random reflector to build up efficient Brillouin lasing resonance along kilometer-long PMFs, yielding four orders of Stokes radiation with high degree of polarization (>99.67%) and polarization extinction ratio of >20 dB. Each Stokes component with kilohertz linewidth as well as over 40-dB optical signal-to-noise ratio has been validated. Compared with single mode fiber-based laser design, the proposed PMF-based laser comb exhibits highly suppressed relative intensity noise, thanks to the immunity to external perturbation and random modes density reduction within polarization-matched Brillouin gain.

Narrow linewidth tunable V-cavity laser using self-injection method

A widely tunable V-cavity semiconductor laser with kilohertz linewidth is demonstrated using simple self-injection method. The tunable laser is packaged into a small-form-factor 9-pin TOSA and can be tuned over 22 channels at 100 GHz spacing with side mode suppression ratios over 36 dB. Self-injection method is used for linewidth reduction by applying optical feedback. Linewidth of the V-cavity laser can be compressed from several megahertz to tens of kilohertz. The linewidth reduction method is essentially channel independent and can be easily realized. It can meet the requirements of many applications such as high-order modulation, coherent communication and sensing.

Noise-immune cavity-enhanced optical heterodyne molecular spectrometry on N₂O 1.283 μm transition based on a quantum-dot external-cavity diode laser.

To access the wavelength within the 1.1-1.3 μm region, we have developed a quantum-dot (QD) laser with an external-cavity configuration and a linewidth of kilohertz at a 1 ms integration time. The residual electroluminescence, due to the inhomogeneous broadening of the QD gain medium, was observed and filtered out using a grating. While a fiber-coupled electro-optical modulator was employed, this laser system was locked to a high-finesse (F∼18,500) optical cavity, and noise-immune cavity-enhanced optical heterodyne molecular spectroscopy was used to observe weak transitions. The Doppler-broadened spectra of a weak N(2)O transition at 1.283 μm are obtained with a signal-to-noise ratio of 30 for a gas pressure of 54 mTorr. The minimum noise-equivalent absorption coefficient is 5.3×10(-10) cm(-1) Hz(-1/2). This system can be a powerful and stable light source for atomic parity nonconservation measurements using thallium, ytterbium, lead, and iodine.

Widely Tunable Narrow-Linewidth Lasers Using Self-Injection DBR Lasers

A widely tunable distributed Bragg reflector (DBR) laser with kilohertz linewidth output is demonstrated using a dual-loop self-injection scheme. The self-injection-locked narrow linewidth DBR laser can be tuned by 13 nm, covering 18 channels, with side mode suppression ratios over 38 dB and linewidths all <10 kHz.

Wideband tunable laser phase noise reduction using single sideband modulation in an electro-optical feed-forward scheme

A wideband laser phase noise reduction scheme is introduced where the optical field of a laser is single sideband modulated with an electrical signal containing the discriminated phase noise of the laser. The proof-of-concept experiments on a commercially available 1549 nm distributed feedback laser show linewidth reduction from 7.5 MHz to 1.8 kHz without using large optical cavity resonators. This feed-forward scheme performs wideband phase noise cancellation independent of the light source and, as such, it is compatible with the original laser source tunability without requiring tunable optical components. By placing the proposed phase noise reduction system after a commercial tunable laser, a tunable coherent light source with kilohertz linewidth over a tuning range of 1530-1570 nm is demonstrated.

External cavity diode laser with kilohertz linewidth by a monolithic folded Fabry–Perot cavity optical feedback

We present a extended-cavity diode laser (ECDL) with kilohertz linewidth by optical feedback from a monolithic folded Fabry-Perot cavity (MFC). In our experiments, an MFC replaces the retroreflecting mirror in the traditional ECDL configuration. Beat-note measurements between this MFC-ECDL and a narrow-linewidth reference laser are performed and demonstrate that the linewidth of this MFC-ECDL is about 6.8 kHz. Phase locking of this MFC-ECDL to the reference laser is achieved with a unity gain as small as 10.2 kHz.

利用Gires-Tournois标准具的色散特性来获得窄线宽激光

A longer laser resonator length is benefit for laser linewidth, but harmful for single-frequency operation. A novel way is suggested to narrow the bandwidth of a Fabry-Perot (FP) cavity through increasing the derivative of one round-trip phase shift with respect to the frequency. It can be implemented by replacing one of two FP mirrors with a Gires-Tournois etalon (GTE), called FPGT, as a dispersion element. FPGT resonator has additional axial modes due to the GTE reflection phase shift. Theoretical analyses show that the bandwidth of additional axial modes can be 1% of that of a conventional FP cavity. A distributed feedback (DFB) laser diode can employ FPGT resonator to achieve ultra-narrow linewidth laser. It is shown that the effect of refractivity fluctuation in the gain medium on the linewidth is little, and kilohertz linewidth is achievable for such a device.

Kilohertz linewidth from frequency-stabilized mid-infrared quantum cascade lasers

Frequency stabilization of mid-IR quantum cascade (QC) lasers to the kilohertz level has been accomplished by use of electronic servo techniques. With this active feedback, an 8.5-microm QC distributed-feedback laser is locked to the side of a rovibrational resonance of nitrous oxide (N(2) O) at 1176.61cm (-1) . A stabilized frequency-noise spectral density of 42Hz/ radicalHz has been measured at 100 kHz; the calculated laser linewidth is 12 kHz.