Injection locking of a 13-W cw Nd:YAG ring laser

Self-seeding of a pulsed double-grating Ti:sapphire laser oscillator

A self-seeded pulsed double-grating Ti:sapphire laser oscillator consisting of a grazing incidence cavity geometry with a pair of gratings and a standing-wave cavity pumped by a frequency-doubled Nd:YAG laser was developed and characterized. With self-seeding, narrow-linewidth single-longitudinal-mode (SLM) operation and SLM scanning were possible with a reduced lasing threshold, which was desirable for the intended applications.

157-nm coherent light source as an inspection tool for F(2) laser lithography

We have developed a 157-nm coherent light source by two-photon resonant four-wave mixing in Xe, with two tunable single-mode 1-kHz Ti:sapphire laser systems at 768 and 681 nm. This light source has been developed to determine the instrumental function of a vacuum ultraviolet spectrometer and to evaluate optical designs for ultra-line-narrowed F(2) laser lithography. The spectral linewidth of the source was less than 0.008 pm (FWHM), with an average power of 0.6 mW.

Single-mode near-infrared optical parametric oscillator amplifier based on periodically poled KTiOPO4

A singly resonant, single-axial-mode, optical parametric oscillator (OPO) based on periodically poled KTiOPO4 (PPKTP) is reported. Signal (1.68 micron) and idler (2.90 micron) optical bandwidths have been narrowed to <400 MHz by use of a diffraction grating at grazing incidence. The OPO generates 370 microJ of signal radiation when pumped by 3.1 mJ of 1.064-micron radiation. We implemented a single-pass PPKTP amplifier to yield 2.15-mJ signal and 1.17-mJ idler radiation without broadening the spectral bandwidths.

Gravitational Wave Detection by Interferometry (Ground and Space)

Significant progress has been made in recent years on the development of gravitational wave detectors. Sources such as coalescing compact binary systems, low-mass X-ray binaries, stellar collapses and pulsars are all possible candidates for detection. The most promising design of gravitational wave detector uses test masses a long distance apart and freely suspended as pendulums on Earth or in drag-free craft in space. The main theme of this review is a discussion of the mechanical and optical principles used in the various long baseline systems being built around the world - LIGO (USA), VIRGO (Italy/France), TAMA 300 (Japan) and GEO 600 (Germany/UK) - and in LISA, a proposed space-borne interferometer.

Widely tunable, narrow-linewidth, subnanosecond pulse generation in an electronically tuned Ti:sapphire laser

Widely tunable subnanosecond Ti:sapphire laser radiation pumped with a cw Q -switched laser-diode-pumped Nd:YAG laser has been demonstrated in a simple laser system with a configuration of variable cavity length. Laser wavelengths can be continuously tuned by adjustment of the rf of an intracavity acousto-optic tunable filter with a computer through the whole range of the laser gain. During tuning of the whole spectral range, there is no need to realign any optics in the laser, except for moving the mirror to track the change of the rf. The peak powers of the output pulses at a pump level of 300 mW are comparable with those of conventional tunable picosecond Ti:sapphire lasers at a cw pump level of almost 10 W.

Pulse amplification of a single-frequency cr:forsterite laser

Stable single-longitudinal-mode operation of a tunable gain-switched Cr:forsterite oscillator-amplifier system is reported. A novel coupled-cavity oscillator configuration provides a low-threshold fluence of 0.3 J cm(-2), making the system attractive for laser media with low gain or high parasitic loss. Nearly transform-limited pulses with instrument-limited bandwidths of 150 MHz have been obtained across a 100-nm wavelength range, limited by the cavity optics. A range of forsterite crystals with Cr(4+) concentration in the 3-21 x 10(18)-cm(-3) range has been used for investigation of amplifier performance in single- and double-pass configurations.

Single-mode tunable Ti:sapphire laser over a wide frequency range

We report a design of a tunable Ti:sapphire laser capable of operating in the range between 700 and 800 nm. The continuous, single-mode tuning is achieved by a pseudoexternal cavity consisting of highly reflective mirrors and a diffraction grating. The advantages of this laser include low operational threshold, a simple configuration that involves only four optical elements, and fine-tuning capabilities. The single longitudinal mode of operation was demonstrated at wavelengths between 695 and 725 nm and was limited by the choice of end mirrors in the laser cavity.

Frequency locking of a pulsed single-longitudinal-mode laser in a coupled-cavity resonator

The performance of a novel resonator that couples a grazing-incidence and a linear cavity is reported. The coupling secures single-longitudinal mode, TEM(00), higher-efficiency and lower-threshold operation. By use of Ti:sapphire as the gain medium, a slope efficiency of 23% and a 100-nm tuning range are reported. A model is explained that fully predicts the mode behavior of the resonator and that can be used to optimize the cavity for single-mode operation. We have developed computer control of the cavity, which is simple in design and is used to lock the <200-MHz bandwidth mode to +/-40 MHz. A 4.8-GHz scan has also been demonstrated.

Lasing threshold reduction in grating-tuned cavities

A new geometry for grating-tuned cavities that reduces optical losses from the gratings, lowers the lasing threshold, and enhances the laser output is described and tested. We achieved these enhancements by feeding back into the cavity light that is normally lost through grating reflections. The new geometry is tested on two grazing-incidence dye laser cavities: one that resembles a Littman -Metcalf design and demonstrates the essential principle of the new arrangement, and one that introduces modifications necessary to allow single-longitudinal-mode operation without mode hopping over a tuning range of ~15 cm-1 .

Low-threshold, single-frequency, coupled cavity Ti:sapphire laser

A novel coupled resonator was developed for narrow-bandwidth, tunable, solid-state lasers. Stable, single-longitudinal-mode, gain-switched titanium:sapphire pulses were obtained across a 130-nm operating range limited by the cavity optics. The low threshold fluence of 0.7 Jcm(-2) makes the cavity attractive for other tunable laser media, particularly when gain is low or parasitic loss is high. A model has been developed that can be used to predict the mode structure of the coupled cavity and for optimization at specific wavelength regions.

Transverse modes in laser cavities terminating in reflective multipass interferometers

The effect of reflective multipass interferometers on the transverse modes of laser cavities equipped with these devices is investigated. We demonstrate, both theoretically and experimentally in a pulsed CO(2) laser, how information on the characteristics of these modes can be directly derived by simply describing these cavities in terms of suitable equivalent geometric parameters. We also discuss and explain the transverse-mode selective properties of these multimirror cavities.

Self-seeding in a dual-cavity-type pulsed Ti:sapphire laser oscillator

We have constructed a self-seeded Ti:sapphire laser oscillator by using a dual-cavity configuration that consists of a Littman configuration cavity and a partially reflecting feedback mirror. This configuration can be decomposed with two kinds of cavity, a grazing-incidence cavity and a standing-wave cavity. The former behaves as an injection seeder and the latter as a slave oscillator. This Ti:sapphire laser system is capable of delivering a continuously tunable laser pulse with a narrow linewidth. Injection at the laser emission region of the free-running Ti:sapphire laser resulted in essentially complete energy extraction.

Accurate frequency-tuning mechanism from a wedge prism in a single-mode tunable laser

We present a new, accurate frequency-tuning mechanism in a grazing-incidence cavity for singlelongitudinal-mode oscillation in a tunable laser. A wedge prism with a small apex angle is inserted between the tuning mirror and the grating for accurate frequency tuning. In this configuration, the laser frequency can be tuned precisely by rotation of the wedge instead of the tuning mirror. This fine-tuning mechanism offers the ability to tune the frequency over more than 400 GHz without mode hop and with a tuning accuracy that is 2 orders of magnitude larger than that of conventional tuning methods.

Two-step selective photoionization of rubidium by using a Ti:sapphire laser

A pulsed Ti:sapphire laser (TSL) is applied for what is, to our knowledge, the first time to laser isotope separation. A collimated beam of a rubidium atom with a natural isotope composition ((85)Rb, 72%; (87)Rb, 28%) is excited selectively from the ground state to the 5(2)P(3/2) state by irradiation of the single-longitudinalmode TSL, and is photoionized by successive UV radiation. Ion spectra of each isotope indicate that each isotope is selectively photoionized.

Longitudinal-mode selectivity and perturbation sensitivity of multimirror laser cavities

Some relevant features of a particular type of multimirror laser cavity, i.e., those cavities terminating in highfinesse reflective multipass interferometers, are theoretically investigated with the aim of highlighting the dependence of the level of spectral control achievable with these cavities on their geometrical and optical characteristics. It is shown that cavities equipped with suitably designed reflective multipass interferometers are not only capable of forcing a laser operation on a single longitudinal mode but can act at the same time as effective emission frequency stabilizers because of their inherently low sensitivity to any perturbation affecting the cavity optical length. This feature is particularly attractive for intrapulse and pulse-to-pulse stabilization of high power pulsed lasers. Criteria are given also for the design of optimized cavities that could simultaneously provide narrow linewidth laser emission and minimize the effects of perturbations.

Control of intrapulse frequency chirping in long-pulse CO(2) lasers employing perturbation-insensitive optical cavities

We present the results of intrapulse frequency chirping measurements that were carried out on a TEA CO(2) laser equipped with various conventional and unconventional frequency-selective optical cavities. We experimentally demonstrate that there is a close relationship between the causes and the extent of intrapulse frequency chirping on the one hand and the type of optical configuration that is used for controlling the laser mode behavior on the other. In particular, it is shown that intrapulse chirping of the emitted frequency can be significantly reduced by employing laser cavities terminating in high-finesse reflective multipass interferometers for single-mode selection. In fact, this type of cavity can be designed in such a way to minimize the effects on the emitted frequency of perturbations affecting the cavity optical length.

External-cavity diode laser using a grazing-incidence diffraction grating

An external cavity has been developed for use with commercial diode lasers. It uses a diffraction grating at grazing incidence for wavelength selection and output coupling. This configuration allows a GaAlAs diode laser to be tuned conveniently anywhere in a range greater than 20 nm. Also, the linewidth is reduced by a factor of more than 1000 from 40 MHz to less than 10 kHz. The new laser system should be useful for high-resolution spectroscopy, laser cooling of atoms, time standards, and coherent optical communications.

Reflective high-finesse interferometers as effective intrapulse laser frequency stabilizers

The effect of optical cavity length perturbations on the intrapulse frequency stability of laser cavities terminating in reflective multipass interferometers is investigated. We demonstrate both theoretically and experimentally, in a long-pulse single-mode TEA CO(2) laser, that intrapulse frequency chirping can be strongly reduced by using relatively long high-finesse interferometers. These results can be applied to the design of single-mode lasers with negligible chirping.

Widely tunable single-longitudinal-mode pulsed dye laser

We have developed a simple cavity-length-stabilization method appropriate for single-longitudinal-mode pulsed lasers that use grazing-incidence gratings. Our technique relies on the detection of aminute (<0.5-mrad) angular variation in the output beam direction caused by a detuning betweenthe cavity-mode frequency and the center frequency of the grating passband. In a prototype systemimplementing this stabilization scheme we have generated single-longitudinal-mode scans of up to 290cm(-1).