Precision radial velocity measurement requires spectral calibration sources that exhibit short to long term wavelength stability and high modal density. Here we report on our efforts to develop a novel 400-1800 nm whispering gallery mode resonator etalon for calibration of optical or infrared spectrographs. The small crystalline MgF2 ring etalon is stable to better than 10-11 levels on 1 s timescales but requires environmental isolation and an referencing to an external standard to maintain long term performance. We will summarize our efforts thus far, as well as the performance achieved over 10 day measurements.
We report on our efforts to develop a whispering gallery mode resonator etalon as a tool for precision radial velocity observations to detect exoplanets. The crystalline MgF2 etalon will be referenced to a compact fiber laser frequency comb, and will serve as the wavelength calibration source for a stabilized, high resolution, visible band spectrograph. The extreme stability required for the detection and characterization of exo-Earths orbiting solar-type stars will be achieved by employing a composite resonator structure with a compensating material to balance the resonator’s coefficients of thermal expansion and thermal refractivity. Progress in modeling the etalon to achieve single mode-like performance, and experiments to demonstrate broad-band (octave-spanning) ling to a white light source, are described.
Narrow-linewidth lasers operating in the near-infrared provide precise timing synchronization for atomic optical clocks and quantum computers. Crystalline ultra-high-Q optical resonators enable high-performance laser design in a small form factor that allow miniaturization of the devices using the lasers. Here we demonstrate a 780 nm self-injection-locked laser with Hertz-level instantaneous linewidth under single-mode continuous-wave operation. The self-injection locking induced by the whispering gallery mode resonator suppresses the frequency noise and reduces the drift of the free running device.
In this work, we investigated the principle of the two-photon absorption (TPA) detection with a loss modulation technique, and first demonstrated the existence of two-photon photoacoustics ultrasound excited by a femtosecond high repetition rate laser. By using the AO modulation with different modulation frequencies, we successfully create the beating of the light signal when the two arms of the beams are both spatial and temporal overlapping. The pulse train of the femtosecond laser causes the narrow band excitation, providing the frequency selectivity and sensitivity. Moreover, the pulse energy is no more than 15nJ/pulse, which is at least 3 orders of magnitude smaller than that of the nanosecond laser, and therefore prevents the thermal damage of the sample. With the help of lock-in detection and a low noise amplifier, we can separate the signal of two-photon absorption from one-photon absorption. We used an ultrasonic transducer to detect the response of the sample, and verified the existence of the two-photon photoacoustics ultrasound generating by the femtosecond laser. Several contrast agents, such as the black carbon solution, the fluorescence dye and the nano-particles, were used in the experiment. In the end, we demonstrated the application, two photo-acoustic imaging, which provides the high spatial resolution (<10μm) and large penetration depth (~1mm), to the simulated biological tissue. This is a milestone to develop the two-photon photoacoustics microscopy, which, in principle, has the great potential to achieve the in vitro and in vivo high resolution deep tissue imaging.
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