The dependence of Raman gain on pump laser bandwidth

The dependence of Raman gain upon laser bandwidth is analyzed in terms of a set of coupled mode equations. The analysis predicts that the Raman gain is independent of pump laser bandwidth within limitations set by dispersion in the Raman medium. These results are verified for rotational and vibrational transitions in H2using a variable bandwidth Nd:YAG laser.     

Laser cavity dumping using an antiresonant ring

A new method for laser cavity dumping using an antiresonant ring laser cavity and an electrooptic phase modulator has been demonstrated on a CO2laser at 10.6 μm. Experimental results are summarized and the cavity and modulator design considerations for this type of cavity dumping are reviewed in this paper. Although the initial experiments were done at 10.6 μm, the antiresonant ring technique may be particularly advantageous for high-power lasers such as ruby and Nd:glass in the visible and near IR. A modified form of the antiresonant ring for accomplishing extremely fast phase switching is also proposed.     

Continuously tuned external cavity semiconductor laser

Continuous tuning (no mode hops) of a grating-tuned external-cavity semiconductor laser by rotation of the grating about a carefully selected point is analyzed and demonstrated using a laser containing a prism beam expander. The analysis predicts the continuous tuning range as a function of pivot-point position and is used to select the point for maximum continuous tuning range. Because dispersive optical elements in the cavity were found to limit the continuous tuning range, the model was modified to include dispersion to first order. The dispersion correction improved the maximum observed tuning range of the 1300-nm-wavelength laser from 600 GHz to nearly 3000 GHz. Details of the cavity and mechanical design as well as pivot-point tolerances are also included     

Bistability in grating-tuned external-cavity semiconductor lasers

Bistability has been observed in the tuning characteristic and power versus current relation of a 1.3 μm grating-tuned external-cavity semiconductor laser. Tuning-direction reversal, current variations, and feedback interruption can change the output power and threshold current at a given wavelength. These effects are shown theoretically to be due to the coupling of the semiconductor gain and index of refraction. From measurements of the semiconductor chip facet reflectivity, solitary laser diode mode spectrum, and tuning curve in the presence of external feedback, the analysis yields values for the external feedback strength, semiconductor modal loss, and linewidth enhancement factor. Using an InGaAsP double-channel-planar-buried-heterostructure laser diode with a 4 percent reflectivity antireflection-coated facet inside an external cavity consisting of a 0.60 numerical aperture lens and a 1200 line/mm diffraction grating, we found 22 percent external feedback, 60 cm^-1modal loss, and a linewidth enhancement factoralpha = -7.1.     

Synchronous acousto-optic tuning of free-space external-cavity lasers

Mechanically tuned external-cavity lasers in which the cavity and the mode filter are tuned synchronously are well known and commercially available. The synchronicity allows phase-continuous tuning to be obtained. Acousto-optic tuning has potential advantages in terms of speed, stability, and precision, but a method for synchronous tuning is required. We propose such a method and describe its experimental verification.     

Design and performance of a reconfigurable liquid-crystal-based optical add/drop multiplexer

The authors describe a reconfigurable optical add-drop multiplexer designed for 50-GHz channel spacing over either the C- or L-bands. The system may also function as a variable optical attenuator. The design features a reflective liquid-crystal modulator, a compact free-space spectrometer, polarization diversity, and fine-scale attenuation control.     

Real-time long range complementary correlation optical time domainreflectometer

The improved performance of an optical time-domain reflectometer (OTDR) through the application of a correlation technique using codes with complementary autocorrelation properties is discussed. The theoretical foundations of the method are presented along with experimental results exhibiting the best one-way range reported to date for a practical long-haul, long-wavelength OTDR system     

Imaging at 3.4 Thz with a quantum-cascade laser

We have assembled a single-frequency imaging system at 3.4 THz with a quantum-cascade laser. Images of electronic and biological applications are demonstrated. We operate the laser with a peak output power of 2.5 mW at a 7% duty cycle and a 22 K operating temperature. The minimum spot size is 340 microm. The signal is detected with a single-element deuterated triglycine sulfate detector, and images are captured by scanning of the sample.