Thresholdless Transition to Coherent Emission at Telecom Wavelengths from Coaxial Nanolasers with Excitation Power Dependent β‐Factors

Abstract

The ongoing miniaturization of semiconductor lasers has enabled ultra-low threshold devices and even provided a path to approach thresholdless lasing with linear input-output characteristics. Such nanoscale lasers have initiated a discourse on the origin of the physical mechanisms involved and their boundaries, such as the required photon number, the importance of optimized light confinement in a resonator, and mode-density enhancement. Here, high-metal-clad coaxial nanolasers, which facilitate thresholdless lasing are investigated. Both the conventional lasing characteristics, as well as the photon statistics of the emitted light at 10 K under continuous wave excitation are experimentally and theoretically investigated. While the former lacks adequate information to determine the threshold to coherent radiation, the latter reveals a finite threshold pump power. The work confirms an important aspect of high-lasers, namely that a thresholdless laser does have a finite threshold pump power and must not be confused with a hypothetical zero-threshold laser. Moreover, the results reveal an excitation power dependent-factor which needs to be taken into account to correctly describe the experimental data. The properties and the terminology of thresholdless lasing have accompanied the development of laser physics in the last decades. More recently, the realization of nanoscale devices

Time‐Resolved Second‐Order Coherence Characterization of Broadband Metallic Nanolasers

“…First, we averaged the second‐order correlation function over the full pump pulses as previously done in the literature. [ 9,15,19 ] To determine the averaged second‐order correlation function, we measured the transition from thermal to coherent photon statistics for increasing optical pump powers ( Figure a,b). It is seen that above the threshold power, i.e., at ≈400 µW, the value of g 2 (0) reaches near‐unity, which clearly suggests the expected CNL coherent emission (Figure 3b).…”

“…It does have a threshold which can be determined by photon statistics analysis. [ 8–10 ] Therefore, for high‐ β NLs, the lasing threshold and coherence properties cannot be inferred from the spectrum and the conventional L–L [ 11,12 ] alone, as high‐ β lasers do not exhibit a clear threshold. Measurements of the second‐order intensity autocorrelation function g 2 ( τ ) [Equation ()] are however able to reveal the lasing threshold, [ 13–15 ] and the transition between SE and lasing regimes as a function of the excitation power.…”

Quantum fluctuations and lineshape anomaly in a high-$β$ silver-coated InP-based metallic nanolaser

“…The experimental coherence time data are extracted from the recorded spectra using a Voigt profile. In contrast to the previously used Pseudo-Voigt lineshape [33], this allows us to establish a clear distinction between Lorentzian (γ L ) and Gaussian (γ G ) FWHM From lowest to highest excitation power-density, the spectra are multiplied with a factor of 400, 30, 2 and 1 respectively for a unified depiction. Panels b) and c) show measured autocorrelation traces for g (2) (τ ) for a pump rate near and well above the laser threshold, respectively.…”

“…In the last decade, an increasing number of publications have established the importance of quantum optical studies on the emission statistics to unambiguously prove lasing operation of high-β emitters [11], [12], [14]- [16], [18], [33]- [42]. In fact, devices working in the regime of amplified spontaneous emission can exhibit linear input-output characteristics without a pronounced kink and significant linewidth narrowing/coherence time increase, which could incorrectly be interpreted as a signature of lasing in a high-β device [14].…”

“Amplified Spontaneous Emission” in Micro- and Nanolasers

“…Superthermal autocorrelation values have also been obtained in metallo-dielectric nanolasers (cf. Figure 4 in [79]).…”