Matthew S. Kirchner

Generation of ultrastable microwaves via optical frequency division

Researchers demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. They generate 10 GHz electrical signals with a fractional frequency instability of ≤8 × 10−16 at 1 s.

Cavity-enhanced optical frequency comb spectroscopy: application to human breath analysis

Broad-bandwidth, high-spectral-resolution optical detection of human breath has identified multiple important biomarkers correlated with specific diseases and metabolic processes. This optical-frequency-comb-based breath analysis system comes with excellent performance in all criteria: high detection sensitivity, ability to identify and distinguish a large number of analytes, and simultaneous, real-time information processing. We demonstrate a minimum detectable absorption of 8 x 10(-10)cm(-1), a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 microm where strong and unique molecular fingerprints exist for many biomarkers. We present a series of breath measurements including stable isotope ratios of CO(2), breath concentrations of CO, and the presence of trace concentrations of NH(3) in high concentrations of H(2)O.

Human breath analysis via cavity-enhanced optical frequency comb spectroscopy

Broad-bandwidth, high-spectral-resolution optical detection of human breath has identified multiple important biomarkers correlated with specific diseases and metabolic processes. This optical-frequency-comb-based breath analysis system comes with excellent performance in all criteria: high detection sensitivity, ability to identify and distinguish a large number of analytes, and simultaneous, real-time information processing. We demonstrate a minimum detectable absorption of 8 x 10(-10)cm(-1), a spectral resolution of 800 MHz, and 200 nm of spectral coverage from 1.5 to 1.7 microm where strong and unique molecular fingerprints exist for many biomarkers. We present a series of breath measurements including stable isotope ratios of CO(2), breath concentrations of CO, and the presence of trace concentrations of NH(3) in high concentrations of H(2)O.

Astronomical spectrograph calibration with broad-spectrum frequency combs

Abstract.Broadband femtosecond-laser frequency combs are filtered to spectrographically resolvable frequency-mode spacing, and limitations of using cavities for spectral filtering are considered. Data and theory are used to show implications relevant to spectrographic calibration of high-resolution, astronomical spectrometers.

Ultralow phase noise microwave generation with an Er:fiber-based optical frequency divider

We present an optical frequency divider based on a 200 MHz repetition rate Er:fiber mode-locked laser that, when locked to a stable optical frequency reference, generates microwave signals with absolute phase noise that is equal to or better than cryogenic microwave oscillators. At 1 Hz offset from a 10 GHz carrier, the phase noise is below -100 dBc/Hz, limited by the optical reference. For offset frequencies >10 kHz, the phase noise is shot noise limited at -145 dBc/Hz. An analysis of the contribution of the residual noise from the Er:fiber optical frequency divider is also presented.

Improved signal-to-noise ratio of 10 GHz microwave signals generated with a mode-filtered femtosecond laser frequency comb

We use a Fabry-Perot cavity to optically filter the output of a Ti:sapphire frequency comb to integer multiples of the original 1 GHz mode spacing. This effectively increases the pulse repetition rate, which is useful for several applications. In the case of low-noise microwave signal generation, such filtering leads to improved linearity of the high-speed photodiodes that detect the mode-locked laser pulse train. The result is significantly improved signal-to-noise ratio at the 10 GHz harmonic with the potential for a shot-noise limited single sideband phase noise floor near -168 dBc/Hz.

Direct diode-pumped Kerr-lens mode-locked Ti:sapphire laser

We describe a Ti:sapphire laser pumped directly with a pair of 1.2W 445nm laser diodes. With over 30mW average power at 800 nm and a measured pulsewidth of 15fs, Kerr-lens-modelocked pulses are available with dramatically decreased pump cost. We propose a simple model to explain the observed highly stable Kerr-lens modelocking in spite of the fact that both the mode-locked and continuous-wave modes are smaller than the pump mode in the crystal.

Frequency stabilization to 6 [times] 10-16 via spectral-hole burning

Researchers demonstrate two-stage laser stabilization based on a combination of Fabry–Perot and spectral-hole burning techniques. The laser was first pre-stabilized using Fabry–Perot cavities and then modulated to address a spectral-hole pattern in Eu3+:Y2SiO5. Taking advantage of the low sensitivity of the spectral holes to environmental perturbations, the researchers obtained a fractional frequency stability of 6 × 10−16

Generation of 20 GHz, sub-40 fs pulses at 960 nm via repetition-rate multiplication

Optical filtering of a stabilized 1 GHz optical frequency comb produces a 20 GHz comb with approximately 40 nm bandwidth (FWHM) at 960 nm. Use of a low-finesse Fabry-Pérot cavity in a double-pass configuration provides a broad cavity coupling bandwidth (Deltalambda/lambda approximately 10%) and large suppression (50 dB) of unwanted modes. Pulse durations shorter than 40 fs with less than 2% residual amplitude modulation are achieved.

Spectrally resolved optical frequency comb from a self-referenced 5 GHz femtosecond laser

In this paper, a self-referenced Ti:sapphire femtosecond laser frequency combs (FLFC) with 5 GHz repetition rate and 230 pJ of pulse energy is reported. The individual modes of the 5 GHz FLFC are dispersed and recorded in a 2D image using a high-resolution spectrometer. This experiment is an important milestone within ongoing efforts to investigate applications in spectroscopy and arbitrary waveform generation with well-stabilized mode-locked femtosecond lasers.