Microlaser-pumped periodically poled lithium niobate optical parametric generator-optical parametric amplifier

For what is believed to be the first time, a single-longitudinal-mode passively Q-switched Nd:YAG microlaser is used to pump a narrow-bandwidth periodically poled lithium niobate (PPLN) optical parametric generator-optical parametric amplifier (OPG-OPA). Before amplification in the OPA, the output of the OPG stage was spectrally filtered with an air-spaced etalon, resulting in spectroscopically useful radiation (bandwidth, ~0.05 cm(-1) FWHM) that was tunable in 15-cm(-1) segments anywhere in the signal range 6820-6220 cm(-1) and the idler range 2580-3180 cm(-1). The ability to pump an OPG-OPA with compact, high-repetition-rate, intrinsically narrow-bandwidth microlasers is made possible by the high gain of PPLN. The result is a tunable light source that is well suited for use in portable spectroscopic gas sensors.     

The onset of coulomb explosions in polyatomic molecules

With the development of high intensity femtosecond lasers, the ionisation and dissociation dynamics of molecules has become an area of considerable interest. Using the technique of femtosecond laser mass spectrometry (FLMS), the molecules carbon disulphide, pyrimidine, toluene, cyclohexanone and benzaldehyde are studied with pulse widths of 50 fs in the near infrared (IR) wavelength region (790 nm). Results are presented and contrasted for laser beam intensities around 10(15) and 10(16) W cm(-2). For the lower intensities, the mass spectra yield dominant singly charged parent ions. Additionally, the appearance of doubly charged parent ions is evident for carbon disulphide, toluene and benzaldehyde with envelopes of doubly charged satellite species existing in these local regions. Carbon disulphide also reveals a small triply charged component. Such atomic-like features are thought to be a strong fingerprint of FLMS at these intensities. However, upon increasing the laser intensity to approximately 10(16) W cm(-2), parent ion dominance decreases and the appearance of multiply charged atomic species occurs, particularly carbon. This phenomenon has been attributed to Coulomb explosions in which the fast absorption of many photons may produce transient highly ionised parent species which can subsequently blow apart. Copyright 1999 John Wiley & Sons, Ltd.     

Uniform molecular analysis using femtosecond laser mass spectrometry

The potential of femtosecond laser time-of-flight mass spectrometry (FLMS) for uniform quantitative analysis of molecules has been investigated. Various samples of molecular gases and vapours have been studied, using ultra-fast ( approximately 50 fs) laser pulses with very high intensity (up to 1.6 x 10(16) Wcm(-2)) for non-resonant multiphoton ionisation/tunnel ionisation. Some of these molecules have high ionisation potentials, requiring up to ten photons for non-resonant ionisation. The relative sensitivity factors (RSF) have been determined as a function of the laser intensity and it has been demonstrated that for molecules with very different masses and ionisation potentials, uniform ionisation has been achieved at the highest laser intensities. Quantitative laser mass spectrometry of molecules is therefore a distinct possibility. Copyright 1999 John Wiley & Sons, Ltd.     

The application of quasi-phase-matched parametric light sources to practical infrared chemical sensing systems

Quasi-phase-matched (QPM) materials allow the generation of spectroscopically useful infrared radiation in an efficient and broadly tunable format. Here, we describe several applications of QPM-based light sources to remote and local chemical sensing. The remote systems are gas imagers that employ a fiber-pumped continuous-wave optical parametric oscillator or a microlaser-pumped, diode-seeded optical parametric amplifier as the illumination source. Technology described for local sensing includes a cavity ring down spectrometer that employs a novel optical parametric generator–amplifier to achieve ≥350 cm^-1 of contiguous tuning and a long-wave infrared light source based on QPM GaAs. In each case the use of QPM materials in conjunction with effective pump sources instills simplicity and ruggedness into the sensing systems. Received: 15 April 2002 / Revised version: 6 June 2002 / Published online: 12 September 2002 RID="*" ID="*"Corresponding author. Fax: +1-925/294-2595, E-mail: tjkulp@sandia.gov RID="**" ID="**"Present address: Corning Inc., Corning, NY 14831, USA RID="*" ID="*"Present address: Corning Inc., Corning, NY 14831, USA RID="**" ID="**"Present address: Blue Leaf Networks, Sunnyvale, CA 94086, USA RID="***" ID="***"Present address: Sandia National Laboratories, Albuquerque, NM 87185, USA     

Periodically poled lithium niobate optical parametric amplifier seeded with the narrow-band filtered output of an optical parametric generator

The results of a simple scheme to generate continuously tunable pulsed narrow-bandwidth (less than 0.1 cm (-1)) light in the infrared are presented. A periodically poled lithium niobate (PPLN) optical parametric amplifier is seeded with the filtered output of a PPLN optical parametric generator. A high-finesse Fabry-Perot etalon is used as the filtering element, giving bandwidths as narrow as 0.08 cm (-1) and tunable over 18 cm (-1) without any adjustments to the PPLN crystals. High efficiency is obtained with a 15-ns 1-kHz Nd:YAG laser, giving energies of up to 180 microJ of signal at 1.6 microm and 60 microJ of idler at 3.3 microm .