Thin-film filter, wavelength-locked, multi-laser cavity for dense wavelength beam combining of broad-area laser diode bars.

We report on individual wavelength locking of a multiplet of 100-µm broad-area laser diode emitters arranged on a 50% fill-factor bar by means of a single external multi-laser cavity using an ultra-narrowband thin-film filter as a dispersive optical element. The achieved wavelength-locked output power is 216 W, corresponding to an electrical-to-optical conversion efficiency of about 49.7%. The 45 emitters of the laser diode bar are stabilized within a spectral range of about 6.4 nm. Our approach is suited for killowatt-class dense wavelength beam combining of direct diode lasers.

C-band waveguide amplifier produced by femtosecond laser writing.

An optical waveguide amplifier fabricated on erbium-ytterbium-doped phosphate glass by direct femtosecond laser writing is demonstrated. The waveguides are manufactured using 1040-nm radiation from a diode-pumped cavity-dumped Yb:KYW oscillator, operating at a 885 kHz repetition rate, with a 350 fs pulse duration. Peak internal gain of 9.2 dB is obtained at 1535 nm, with a minimum internal gain of 5.2 dB at 1565 nm. Relatively low insertion losses of 1.9 dB enable for the first time an appreciable net gain in the full C-band of optical communications.

Diode-pumped femtosecond laser oscillator with cavity dumping.

We report on a diode-pumped tunable Yb:glass femtosecond laser oscillator with electro-optic cavity dumping. Pulses with energies exceeding 400 nJ and peak powers greater than 1 MW were generated at repetition frequencies as high as 200 kHz. This laser forms a compact light source for various scientific and industrial applications such as micromachining.

Dual effects of glucagon and cyclic AMP on DNA synthesis in cultured rat hepatocytes: stimulatory regulation in early G1 and inhibition shortly before the S phase entry.

Although several lines of evidence implicate cyclic AMP in the humoral control of liver growth, its precise role is still not clear. To explore further the role of cyclic AMP in hepatocyte proliferation, we have examined the effects of glucagon and other cyclic AMP-elevating agents on the DNA synthesis in primary cultures of adult rat hepatocytes, with particular focus on the temporal aspects. The cells were cultured in a serum-free, defined medium and treated with epidermal growth factor (EGF), insulin, and dexamethasone. Exposure of the hepatocytes to low concentrations (10 pM-1 nM) of glucagon in the early stages of culturing (usually within 6 h from plating) enhanced the initial rate of S phase entry without affecting the lag time from the plating to the onset of DNA synthesis, whereas higher concentrations inhibited it. In contrast, glucagon addition at later stages (24-45 h after plating) produced only the inhibition. Thus, if glucagon was added at a time when there was a continuous EGF/insulin-induced recruitment of cells to S phase, the rate of G1-S transition was markedly decreased within 1-3 h. This inhibitory effect occurred at low glucagon concentrations (ID50 less than 1 nM) and was mimicked by cholera toxin, forskolin, isobutyl methylxanthine, and 8-bromo cyclic AMP. The results indicate that cyclic AMP has dual effects on hepatocyte proliferation with a stimulatory modulation early in the prereplicative period (G0 or early G1), and a marked inhibition exerted immediately before the transition from G1 to S phase.

Quantitative aspects of the effects of insulin, epidermal growth factor and dexamethasone on DNA synthesis in cultured adult rat hepatocytes.

Epidermal growth factor (EGF) and insulin in combination have previously been shown to initiate S-phase in primary cultures of adult rat hepatocytes. We here describe the detailed time course and dose-dependency of the effects of EGF and insulin on DNA synthesis in cultured hepatocytes. The DNA synthesis was assessed either biochemically or autoradiographically with a fairly good correlation between the two methods. DNA synthesis started 24-30 h after plating of the cells and peaked at approximately 70 h. Up to 70% of the cells entered DNA synthesis during this period. EGF and insulin acted synergistically on the DNA synthesis. Dexamethasone raised the DNA synthesis slightly, maximal effect occurred at concentrations above 2.5 nM and this agent was routinely used in the experiments with EGF and insulin. In the presence of 0.4 microM insulin from the time of plating, EGF dose-dependently increased the DNA synthesis with maximal effect at 5-15 nM. When added in combination with 1.7 nM EGF, insulin enhanced the DNA synthesis over the concentration range from 0.1 to 3 nM. These studies show that primary cultures of hepatocytes are useful in assessing the quantitative aspects of the interactions between the growth stimulating effects of hormones.