Investigations of the attenuation coefficient of a narrow-bandwidth pulsed laser beam in water.

The attenuation coefficient of a pulsed laser beam in water is investigated experimentally. It is found that the attenuation coefficient is dependent on the pulse energy and the linewidth of the laser, rather than a constant. The attenuation coefficient for a narrow linewidth laser can exceed that of a broad linewidth laser due to stimulated Brillouin scattering when the laser intensity is larger than a certain value. A theoretical analysis is provided.

Generation of Fourier-transform-limited 35-ns pulses with a ramp-hold-fire seeding technique in a Ti:sapphire laser.

We report on an injection-seeded Ti:sapphire laser pumped by the second harmonic of a Nd:YAG laser. The resonance between the low-power seed laser and the slave cavity is achieved by a ramp-hold-fire technique. Because of the triangular cavity design, the spatial beam profile is excellent; and combined with the narrow-linewidth pulses, the conversion efficiencies for nonlinear frequency generation are excellent.

Generation of near-Fourier-transform-limited high-energy pulses in a chain of fiber-bulk amplifiers.

We demonstrate the generation of high-power near-Fourier-transform-limited pulses with variable pulse duration in the nanosecond regime through a combination of fiber and bulk amplification. The fiber amplifier consists of a dual-stage fiber amplifier based on Nd- and Yb-doped single- and double-clad fibers. The bulk amplifier consists of a four-pass, flash-lamp-pumped Nd:YAG rod. Since no resonance condition is required for locking of the seed source to a slave cavity, the setup is extremely rugged.

On the etalon effect generated by a Pockels cell with high-quality antireflection coatings.

We discuss the modulation in the spectrum generated by the windows of a Pockels cell. Although they are antireflection coated, the residual reflectivity of the highly parallel window faces can still have etalon effects that lead to pronounced spectrum modulation. This problem is easily solved by the use of slightly wedged windows.

Visible and near-ultraviolet absorption spectrum of liquid water: comment.

Measurements of the absorption of pure water have been described [Appl. Opt. 38, 1216 (1999)]. This comment on that paper disputes the claims that (1) their list of references on pure water absorption is complete, (2) their result "...provides reliable data in the 320-420-nm region...," and (3) their data agree well with existing data in the literature. The clearest demonstration of these points is made by plotting their data and its associated error bars together with plots of other data in the literature that should be considered significantly more reliable. Finally, for practical applications that require absorption data, a suggestion is made for the best choice of absorption coefficients in the range of 196 nm

Reply to criticisms of the Pope and Fry paper on pure water absorption made in a comment by Quickenden et al.

The measurements of the absorption spectrum of pure water in a paper by Pope and Fry [Appl. Opt. 36, 8710 (1997)] have been criticized by Quickenden et al. [Appl. Opt. 39, 2740 (2000)]. These criticisms are answered.

Synchronous, dual-wavelength, injection-seeded amplification of 5-ns pulses in a flash-lamp-pumped Ti:sapphire laser.

The outputs of two cw diode lasers are coupled into a flash-lamp-pumped Ti:sapphire laser cavity for regenerative amplification. Slices of each seed beam are simultaneously trapped in the cavity and amplified for approximately 33 round trips. The output is a 4.7-ns pulse, the total pulse energy is 110 mJ, and linewidths are only 50% greater than the Fourier-transform limit. The timing jitter between the pulses at the two wavelengths is less than +/-75 ps , and their relative energy is controlled by adjustment of the seed power of the cw diode lasers. Gain competition between the two frequencies does not lead to instabilities.

Angle-tuned type II external-cavity frequency doubling without temperature stabilization.

We report frequency doubling of a low-power cw diode laser at 1064 nm in an external ring cavity by use of an angle-tuned KTP type II crystal. We demonstrate a new setup that requires no temperature stabilization of the crystal. An intracavity lambda/2 plate rotates the polarization of the fundamental after each cavity round trip by 90 degrees; this provides the two eigenpolarizations of the crystal required for a type II nonlinear process. As a result, it is possible to maintain the resonance condition by use of a standard locking circuit.

Ultranarrow-linewidth, efficient amplification of low-power seed sources by a fiber amplifier.

We report efficient amplification of an external cavity diode laser in the 1.06-microm range. The diode laser radiation is coupled into a Nd-doped silica fiber. The fiber is pumped by a diode array with up to 6.15 W of power. After a single pass of the seed radiation through the fiber amplifier, we observe up to 1.74 W of single-mode, narrow-linewidth laser radiation that is tunable over a relatively wide range of 1.060-1.067 microm. The output from our amplifier has the same spectral characteristics as the seed beam.

Accuracy limitations on Brillouin lidar measurements of temperature and sound speed in the ocean.

There are five mutually dependent variables relevant to Brillouin lidar measurements of temperature and sound speed in the ocean; they are (1) the Brillouin shift, (2) the sound speed, (3) the index of refraction, (4) the temperature, and (5) the salinity. We use three well-known relations to analyze rigorously the interdependence of these five variables. Clearly, a Brillouin shift measurement does not provide a stand-alone determination of temperature or sound speed; one more variable or one more relation must be known. The use of mean values of salinity that have been obtained by an analysis of a large set of historical in situ data is considered for this additional relation.

Absorption spectrum (340-640 nm) of pure water. I. Photothermal measurements.

We measured the absorption spectrum (340-640 nm) of the purest available water with photothermal deflection spectroscopy. Our spectrum exhibits an absorption minimum in the blue region of the spectrum that is deeper than in most previously documented pure-water absorption studies. We attribute this to exceptional sample purity and our technique's inherent freedom from scattering effects. Because the absorption minimum is significantly lower, our spectrum displays high-order molecular resonance structure not observed in any previous absorption studies to our knowledge. We find the minimum in the absorption spectrum of pure water is 0.0062 ? 0.0006 m(-1) at 420 nm and 25 degrees C.

Absorption spectrum (380-700 nm) of pure water. II. Integrating cavity measurements.

Definitive data on the absorption spectrum of pure water from 380 to 700 nm have been obtained with an integrating cavity technique. The results are in good agreement with those recently obtained by our group with a completely independent photothermal technique. As before, we find that the absorption in the blue is significantly lower than had previously been generally believed and that the absorption minimum is at a significantly shorter wavelength, i.e., 0.0044 ? 0.0006 m(-1) at 418 nm. Several spectroscopic features have been identified in the visible spectrum to our knowledge for the first time.

Angular distribution of the forward light scattering from a quartz fiber.

Using a new technique based on the fanning of a coherent light beam in a photorefractive BaTiO(3) crystal, we have measured the angular distribution of forward light scattering by quartz fibers of radii from 15 to 30 µm. Data have been obtained over the angular range 0° to 0.3° and are in good agreement with theory.

Empirical equation for the index of refraction of seawater.

We have determined an empirical equation for the index of refraction of water as a function of temperature, salinity, and wavelength at atmospheric pressure. The experimental data selected by Austin and Halikas ["The index of refraction of seawater," SIO Ref. 76-1 (Scripps Institution of Oceanography, La Jolla, Calif., 1976)] were fitted to power series in the variables. A ten-parameter empirical equation that reproduces the original data to within its experimental errors was obtained.

Directed positioning of micronuclei in Paramecium tetraurelia with laser tweezers: absence of detectible damage after manipulation.

Possible covert damage from the use of the laser optical force trap (laser tweezers) to reposition micronuclei in Paramecium tetraurelia was assessed by measuring proliferation rates and postautogamous survival and mutation rates of cells after laser manipulations. No differences in subsequent daily proliferation rates among laser manipulated and various control classes of cells were seen. Similarly, the rates of postautogamous lethality and of "slow growth mutations" after repositioning of both micronuclei were not different from such rates in unmanipulated controls. In spite of extensive manipulations of micronuclei by the laser tweezers, there is no evidence of any damage induced by these manipulations. The laser tweezers therefore appears to be a tool of benign effect upon living cells, with tremendous potential use in many cell and developmental biological investigations.

Integrating cavity absorption meter.

Scattering effects have always been an important systematic problem in absorption measurements. A new integrating cavity absorption meter has been developed that, in principle, is rigorously independent of scattering effects. The theoretical basis for this integrating cavity device is developed and applied to a generic experimental device: a one-dimensional model is described that demonstrates qualitatively the observed deviations from ideal; details of an actual device are provided; and experimental results for the absorption coefficient of aqueous solutions with various absorptions and with various concentrations of scatterers are presented.

Single frequency operation of an injection-seeded Nd:YAG laser in high noise and vibration environments.

We report on an experimental demonstration of single frequency operation of an injection-seeded Nd:YAG laser in a high noise and vibration environment.

Derivation and measurement of the reversible temporal lengthening of femtosecond optical pulses for the case of a four-prism sequence.

An expression is derived for the reversible lengthening of optical pulse durations from the order of 50 fsec to the order of 500 fsec by a four-prism sequence and focusing elements. This temporal lengthening is caused by spatial dispersion of the different frequency components transverse to the direction of propagation at the symmetry plane of the prism sequence. Experimental measurements of the pulse lengthening agree well with calculated values.