Showing papers by "Brian J. Orr published in 2004"

Rapid measurement of cavity ringdown absorption spectra with a swept-frequency laser

Abstract: A novel cavity ringdown spectrometer, incorporating a miniature continuous-wave swept-frequency laser that is widely tunable, requires less than 1 s to record wide-ranging absorption spectra with high sensitivity in a single rapid sweep of the laser frequency. The free spectral range of the ringdown cavity defines a sampling grid to measure absorbance-dependent ringdown times at successive cavity-resonance frequencies. The spectrometer has a single-ended transmitter-receiver configuration based on retro-reflected optical-heterodyne detection and exploiting fibre-optical telecommunications components. This swept-frequency approach to cavity ringdown spectroscopy yields a simple, low-cost, compact, rugged, versatile instrument for efficient sensing of gases. The performance of the spectrometer is demonstrated by measuring weak near-infrared rovibrational spectra of carbon dioxide gas within the 1.5–1.6 μm wavelength range.

Control of frequency chirp in nanosecond-pulsed laser spectroscopy. 1. Optical-heterodyne chirp analysis techniques

Abstract: We evaluate ways to analyze optical-heterodyne measurements of frequency chirp in pulsed, single-longitudinal-mode output from lasers (or other coherent light sources) that operate on nanosecond time scales. The instantaneous frequency is extracted from the beat signal generated between a continuous-wave reference beam and the output of the pulsed source. Three analysis techniques are tested: Fourier-transform, direct curve fitting, and electronic mixing. We use synthetic beat waveforms based on actual experimental parameters to evaluate the three methods and apply these chirp-measurement techniques to an injection-seeded optical parametric oscillator system.

Transition from single-mode to multimode operation of an injection-seeded pulsed optical parametric oscillator.

Abstract: Optical-heterodyne measurements are made on ~842-nm signal output of an injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 pumped at 532 nm by long (~27-ns) pulses from a Nd:YAG laser At low pump energies (≤25 times the free-running threshold), the narrowband tunable OPO output is single-longitudinal-mode (SLM) and frequency chirp can be <10 MHz, much less than the transform-limited optical bandwidth (~175 MHz) We explore the transition from SLM operation to multimode operation as pump energy or phase mismatch are increased, causing unseeded cavity modes to build up later in the pulse

Control of frequency chirp in nanosecond-pulsed laser spectroscopy. 2. A long-pulse optical parametric oscillator for narrow optical bandwidth

Abstract: An injection-seeded optical parametric oscillator (OPO) based on periodically poled KTiOPO4 is pumped at 532 nm by relatively long (~27-ns) pulses from a specially constructed Nd:YAG laser. This pulsed OPO system generates continuously tunable, single-longitudinal-mode output at signal wavelengths near 842 nm, which is suitable for high-resolution spectroscopy. Optical-heterodyne measurements show that chirp in the instantaneous frequency of the pulsed OPO signal output radiation increases linearly as the seed frequency is detuned from the free-running (unseeded) OPO frequency. The frequency chirp can be maintained below 10 MHz, which is substantially less than the Fourier-transform-limited optical bandwidth (17.5 MHz full width at half-maximum for a 25-ns OPO signal pulse) and is insensitive to variation of the fluence of the pump radiation. The effects of detuning the OPO cavity length from resonance with the seed frequency and the onset of partially seeded OPO operation are also investigated.

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator based on a self-adaptive, phase-conjugate cavity mirror.

Abstract: Narrowband tuning of a pulsed optical parametric oscillator (OPO) is achieved with a self-adaptive injection-seeded optical cavity employing a phase-conjugate reflector. This approach is used in a novel OPO system based on periodically poled KTiOPO4 and pumped at 532 nm by a pulsed Nd:YAG laser. The OPO is injection seeded at 835–855 nm by a continuous-wave tunable diode laser, which also enables a Rh:BaTiO3 photorefractive crystal to act as a wavelength-selective phase-conjugate reflector, with no need for active control of cavity length. The single-longitudinal-mode tunability and operational simplicity of this OPO system are demonstrated experimentally.

An injection-seeded self-adaptive optical resonant cavity and a method of generating coherent light

Abstract: An apparatus and a method are described for providing a pulsed beam of narrowband coherent light. The apparatus (210) includes an optical gain medium (212) disposed inside an optical cavity (230) formed by a reflector (214) and a second optical medium (216). The cavity (230) is injection seeded by an input seed beam (220) of coherent light that is injected through a side of the second optical medium (216) opposite a side that faces the optical cavity (230), whereby the second optical medium (216) becomes partially reflective to light in the optical cavity (230) that has a wavelength which is about the same as the wavelength of the input seed beam and that overlaps spatially and temporally, in the second optical medium (216), with the input seed beam (220), and whereby the optical cavity (230) becomes resonant in respect of such light in the optical cavity (230).

Cavity ringdown spectroscopy with optical-heterodyne detection and miniature external-cavity tunable lasers

Abstract: Miniature external-cavity tunable lasers are combined with retro-reflected optical-heterodyne detection for rapidly swept, continuous-wave cavity ringdown spectroscopy. This yields a compact, rugged, versatile, high-performance instrument for efficient spectroscopic sensing of gases

Narrowband tuning of an injection-seeded pulsed optical parametric oscillator with a self-adaptive optical cavity

Abstract: A novel self-adaptive optical cavity with a phase-conjugate reflector is used for injection-seeded narrowband tuning of a pulsed optical parametric oscillator, eliminating the need for damage-prone intracavity tuning elements or active cavity control.

Chirp characterization of a high-resolution, low-chirp, ns-pulsed optical parametric oscillator/amplifier system

Abstract: An injection-seeded pulsed optical parametric oscillator is amplified and the frequency chirp characterized using optical heterodyne techniques. The low-chirp 842-nm signal output depends only slightly on amplifier pump energy, suitable for high-resolution spectroscopy.