ABSTRACT
Frequency combs have made optical metrology accessible to hundreds of laboratories worldwide and they have set new benchmarks in multi-species trace gas sensing for environmental, industrial and medical applications. However, current comb spectrometers privilege either frequency precision and sensitivity through interposition of a cw probe laser with limited tuning range, or spectral coverage and measurement time using the comb itself as an ultra-broadband probe. We overcome this restriction by introducing a comb-locked frequency-swept optical synthesizer that allows a continuous-wave laser to be swept in seconds over spectral ranges of several terahertz while remaining phase locked to an underlying frequency comb. This offers a unique degree of versatility, as the synthesizer can be either repeatedly scanned over a single absorption line to achieve ultimate precision and sensitivity, or swept in seconds over an entire rovibrational band to capture multiple species. The spectrometer enables us to determine line center frequencies with an absolute uncertainty of 30 kHz and at the same time to collect absorption spectra over more than 3 THz with state-of-the-art sensitivity of a few 10-10 cm-1. Beyond precision broadband spectroscopy, the proposed synthesizer is an extremely promising tool to force a breakthrough in terahertz metrology and coherent laser ranging.
ABSTRACT
We characterize an Er:fiber laser frequency comb that is passively carrier envelope phase-stabilized via difference frequency generation at a wavelength of 1550 nm. A generic method to measure the comb linewidth at different wavelengths is demonstrated. By transferring the properties of a comb line to a cw external cavity diode laser, the phase noise is subsequently measured by tracking the delayed self-heterodyne beat note. This relatively simple characterization method is suitable for a broad range of optical frequencies. Here, it is used to characterize our difference frequency generation (DFG) comb over nearly an optical octave. With repetition-rate stabilization, a radiofrequency reference oscillator limited linewidth is achieved. A lock to an optical reference shows out-of-loop linewidths of the comb at the hertz level. The phase noise measurements are in excellent agreement with the elastic tape model with a fix point at zero frequency.
ABSTRACT
We present a simple method for narrowing the intrinsic Lorentzian linewidth of a commercial ultraviolet grating extended-cavity diode laser (TOPTICA DL Pro) using weak optical feedback from a long external cavity. We achieve a suppression in frequency noise spectral density of 20 dB measured at frequencies around 1 MHz, corresponding to the narrowing of the intrinsic Lorentzian linewidth from 200 kHz to 2 kHz. Provided additional active low-frequency noise suppression and long-term drift compensation, the system is suitable for experiments requiring a tunable ultraviolet laser with narrow linewidth and low high-frequency noise, such as precision spectroscopy, optical clocks, and quantum information science experiments.
ABSTRACT
We report on the realization of a continuous-wave light source based on nonlinear interaction in KBBF at a wavelength of 191 nm. More than 1.3 mW of deep-ultraviolet power was generated in a mechanically robust setup pumped by an amplified grating stabilized diode laser. Mode hop-free tuning over 40 GHz at 191 nm could be demonstrated.
Subject(s)
Lasers, Solid-State , Lighting/instrumentation , Equipment Design , Equipment Failure AnalysisABSTRACT
We report on nonlinear optical properties of a p-i-n junction quantum dot saturable absorber based on InGaAs/GaAs. Absorption recovery dynamics and nonlinear reflectivity are investigated for different reverse bias and pump power conditions. A decrease in absorption recovery time of nearly two orders of magnitude is demonstrated by applying a voltage between 0 and -20 V. The saturable absorber modulation depth and saturation fluence are found to be independent from the applied reverse bias.
ABSTRACT
Live microscopy techniques (i.e., differential interference contrast, confocal microscopy, etc.) have enabled the understanding of the mechanisms involved in cells and tissue formation. In long-term studies, special care must be taken in order to avoid sample damage, restricting the applicability of the different microscopy techniques. We demonstrate the potential of using third-harmonic generation (THG) microscopy for morphogenesis/embryogenesis studies in living Caenorhabditis elegans (C. elegans). Moreover, we show that the THG signal is obtained in all the embryo development stages, showing different tissue/structure information. For this research, we employ a 1550-nm femtosecond fiber laser and demonstrate that the expected water absorption at this wavelength does not severely compromise sample viability. Additionally, this has the important advantage that the THG signal is emitted at visible wavelengths (516 nm). Therefore, standard collection optics and detectors operating near maximum efficiency enable an optimal signal reconstruction. All this, to the best of our knowledge, demonstrates for the first time the noninvasiveness and strong potential of this particular wavelength to be used for high-resolution four-dimensional imaging of embryogenesis using unstained C. elegans in vivo samples.
