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We report on the first demonstration of an optical waveguide amplifier in phospho-tellurite glass providing net gain at 1.5 μm. The device was fabricated using a high repetition rate femtosecond laser and exhibited internal gain across 100-nm bandwidth covering the entire C + L telecom bands.

We report on fs-laser micromachining of active waveguides in a new erbium-doped phospho-tellurite glass by means of a compact cavity-dumped Yb-based writing system. The spectroscopic properties of the glass were investigated, and the fs-laser written waveguides were characterized in terms of passive as well as active performance. In particular, internal gain was demonstrated in the whole C+L band of optical communications (1530- 1610 nm).

An extremely compact and versatile near-infrared two-color femtosecond pump-probe spectroscopy apparatus based on an amplified Erfiber laser system is presented and applied to the characterization of the relaxation dynamics of single-wall carbon nanotubes with fundamental absorption in the 2 microm spectral region. By implementing a fast-scan technique, dynamics as long as 3 ps are acquired in 5 s with a relative sensitivity of 10(-4) and a temporal resolution below 100 fs at 2 microm.

We demonstrate passive mode-locking by means of a semiconductor saturable-absorber mirror in a diode-pumped Yb:YLF laser. We present crystal growth process, spectroscopic measurements, and investigation of mode-locking performance. Pulse trains with minimum duration of 196 fs, average power of 54 mW and a repetition rate of 55 MHz were obtained. The optical spectrum, centered at 1028 nm, has a 7.1-nm bandwidth leading to nearly transform-limited pulses.

Laser irradiation of tissues treated in vivo with the hematoporphyrin derivative (HPD) is known to result in a cytocidal effect, reportedly more pronounced in the tumor than in the surrounding normal tissues. In order to ascertain if this phenomenon had a clear cellular basis, it has been now reproduced in vitro in a model system consisting of normal and transformed cell lines. Epithelial rat thyroid cells were infected and transformed with a RNA oncogenic virus. Both the original (normal) and the viral-transformed (tumorigenic) cells were incubated with HPD and exposed to two types of laser irradiation: 631 nm, continuous wave; and 337.1 nm, pulsed. Under the conditions tested, the percentage survival of the transformed cells was found to be lower (up to approximately 3 times) than that of the normal cells. The cytocidal effect was greater using the pulsed than using the continuous-wave irradiation. The difference between normal and tumor cells was more evident at 30 micrograms than at 50 micrograms of HPD per ml. The HPD not followed by laser irradiation had no effect on the cell growth rate. The findings of a significant difference in the sensitivity to photoactivated HPD between normal and tumor cells under strictly controlled and highly comparable conditions opens new possibilities to the study of the cellular and molecular mechanisms involved in the phototherapy of tumors. Furthermore, studies in vitro on the active components of the photosensitizer and on their selectivity towards the tumor cells, explained at a cellular level, will lead to better approaches to photochemotherapy in vivo.

We report on the absolute frequency measurement of an extended-cavity diode laser stabilized against a Doppler-free vibration-rotation transition of the HO isotopologue near 1.384 μm. Absolute determination is performed by comparing the water-stabilized laser frequency with respect to a GPS-disciplined Rb microwave standard by means of a self-referenced fiber-based optical frequency comb. The line center frequency of the 2→2 transition of the HO ν+ν combination band is found to be 216 519 045 955(13) kHz. [ABSTRACT FROM AUTHOR]

Passive mode-locking operation of a diode-pumped Tm:GdLiF laser is demonstrated over a wide wavelength tuning range, from 1868 to 1926 nm, using an InGaAs quantum wells saturable absorber. Pulse trains with a minimum duration of 17 ps and a repetition rate of 86 MHz have been obtained. A maximum output power of 270 mW has been achieved with a longer pulse duration of 44 ps. [ABSTRACT FROM AUTHOR]

We present a comparative analysis on the growth, the spectroscopic features, and the cw laser action of room-temperature Yb(5%):LiYF4 (YLF) and Yb(10%):KYF4 (KYF) crystals. Optical slope efficiencies of 33% and 52% have been demonstrated for Yb:YLF and Yb:KYF crystals, respectively. A remarkable wide wavelength tunability from 1.01 to 1.07 μm has been obtained for both laser crystals. [ABSTRACT FROM AUTHOR]

Robust single-frequency operation of an erbium-ytterbium glass waveguide laser based on the twisted-mode technique is demonstrated. A single-mode output power of ~0.7 mW with relative-intensity-noise peak value of -90 dB/Hz has been obtained. [ABSTRACT FROM AUTHOR]

We developed a low-noise, single-frequency Tm–Ho:YAG laser tunable in the wavelength interval between 2087 and 2099 nm. To suppress both amplitude and frequency fluctuations the laser has been stabilised by two different control loops. Intensity noise has been effectively reduced using a feedback loop acting on the pump diode current, based on a biquadratic bandpass filter, which provides up to 17 dB suppression at the relaxation oscillation peak. Absolute frequency stabilisation has been achieved by locking the oscillator to the P(12) absorption line of the HBr molecule at 2097.2 nm using the fringe side locking technique, obtaining a long-term frequency stability better than 32 kHz over an observation time of 60 min. This stabilised source is aimed to injection seeding of a coherent lidar system for high precision measurements of wind velocity. [Copyright &y& Elsevier]

Abstract. Experimental results are reported for the noise characteristics of an Yb-doped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narrow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum output power of the amplifier is 1.2W with a gain larger than 30 dB. An increase of the intensity-noise spectral density relative to the signal, by approximately 6.5 dB, is introduced by the amplification process, due to signal-amplified spontaneous-emission (ASE) beat noise. A remarkable increase of the noise level with decreasing frequency is observed below Is approximately equal to 35 kHz, probably due to technical noise of the amplifier pump diodes. The spectral broadening due to amplifier phase noise was measured to be less than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kHz-linewidth diode laser at 1083 nm is therefore expected to be in the same range. [ABSTRACT FROM AUTHOR]

Abstract. A comprehensive analysis of the mechanisms inducing intensity noise in a single-frequency, diode-pumped erbium--ytterbium glass laser is presented. Owing to the energy transfer between the codopant and the active material, the Er:Yb laser shows a markedly reduced sensitivity to pump power fluctuations, and hence its intensity noise spectrum is mainly determined by the fluctuations in the cavity losses. The experimental measurements confirm the results of the theoretical analysis. [ABSTRACT FROM AUTHOR]

A comprehensive review of the work done by our group, during the last few years, on diode-pumped cw operating bulk Er : Yb phosphate glass is presented. The high performance of this laser in terms of output power, laser slope efficiency, single longitudinal and transverse mode operation, laser tunability and frequency stability, amplitude noise, and active mode-locking operation, are considered. The combination of this high performance and potential low cost makes these laser devices attractive for a variety of applications including spectroscopy, metrology, optical radars, optical communications, and all optical switching. [ABSTRACT FROM AUTHOR]

Demonstrates the frequency stabilization of tunable erbium-ytterbium microlasers to absorption lines of acetylene. Usage of two-sample Allan variance of the heterodyne beat-note signal; Value of the Allan variance square root; Magnitude of oscillator spacing.

Two identical diode-pumped bulk Er–Yb:glass lasers, operating at 1534-nm wavelength, have been independently locked to the P(15) rovibrational line of the acetylene molecule by the FM sideband technique. Measurements of the beat note between the two lasers show a long-term frequency stability of 170 kHz over a 1-h period and a short-term laser linewidth below 50 kHz over 1 ms. The Allan standard deviation of the beat frequency was measured yielding values below 10[sup -10] for integration times between 10 ms and 1 s, reaching the 4×10[sup -11] level at 0.1 s. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper we present recent results obtained on the generation of ultra-high repetition rate optical pulse trains at 1.5 μm in asynchronously frequency-modulated Er–Yb : glass lasers. Nearly transform-limited pulse trains at either single or dual carrier wavelength with repetition rates up to ∼20 GHz are generated by means of an external fiber Bragg grating. These pulse trains are of great potential interest for soliton-based optical transmission systems. [Copyright &y& Elsevier]

We present the growth and the room-temperature spectroscopic analysis of three fluoride hosts, namely BaY2F8, LiYF4 and KYF4, equally codoped with 5.2% thulium and 0.5% holmium, together with the cw laser results in the 2 μm wavelength region of BaYF and YLF at room temperature. A comparison is carried out between the three crystals, showing the higher slope efficiency of YLF-laser, the wider tunability range of BaYF-laser, and the promising 170-nm broad-band emission of KYF at around 2 μm. [Copyright &y& Elsevier]