Michael M. Salour

Picosecond laser interaction with metallic zirconium

UV laser pulses of two picosecond duration have been used to observe photoelectric emission and thermally enhanced photoelectric emission from a zirconium metal surface. The data show that the electron and lattice temperature remain approximately equal and the electron‐phonon energy relaxation time is less than 1 ps.

Optically pumped semiconductor platelet lasers

Tunable CW laser action of platelet semiconductors is reported in both mode-locked and unmode-locked configurations. The gain media are platelets of CdS, CdSe, CdSSe, and InGaAsP cooled to 85 K and longitudinally pumped by an argon-ion laser. Antireflection (AR) coating of the crystal face and external bandwidth restriction have been used to generate pulses as short as 4 ps. The pulses observed are chirped, with nontransform limited time-bandwidth products of about 1.7. The energy conversion efficiency is 20 percent into the TEM 00 mode, with output powers of over 10 mW from CdS.

Generation, stabilization, and amplification of subpicosecond pulses

A sync-pumped cw dye laser system has been used to produce subpicosecond pulses. Pulses as short as 0.7 ps, assuming a single-sided exponential pulse shape, were observed. A set of experiments was performed to investigate the origin and effects of noise in the sync-pumped system. A digital and an analog feedback loop have been designed to optimize the pulse width. The noise has been lowered by 10 dB for frequencies up to 10 kHz; long-term drift is also controlled by this method. A four-stage dye laser amplifier, pumped by a Nd:YAG laser which operates at a 10-Hz repetition rate, is synchronized electronically to the dye-laser picosecond pulses. A gain of 3×106 has been achieved.

Pulse‐width stabilization of a synchronously pumped mode‐locked dye laser

Using an analog feedback loop acting on the mode‐locker frequency of a synchronously pumped mode‐locked dye laser, we have observed a substantial decrease of pulse‐width variations at frequencies up to 10 kHz at the cost of an increase in higher‐frequency noise. A digital loop acting on the cavity length decreased noise at low frequencies. Using these methods, we have generated reproducible and stabilized frequency‐tunable subpicosecond pulses, and have determined the effects of noise in the mode‐locking frequency of the pumping Ar+ laser and drift in the cavity length of the dye laser.

Optically pumped CW semiconductor ring laser

An optically pumped semiconductor ring laser having a plurality of reflective elements optically aligned with one another to form a ring-shaped resonant cavity. A semiconductor lasing medium is mounted within the ring-shaped resonant cavity by a transparent, heat conductive mount located within a vacuum/cooling chamber of the type which allows the passage of a laser beam therethrough. A pump beam initiates a lasing action within the ring-shaped resonant cavity to produce said laser beam and said laser beam exits the resonant cavity as a pair of outputs. An alternate embodiment of the above described semiconductor ring laser provides a semblance of unidirectional lasing operation.

Turnable cw bulk semiconductor platelet laser

We report the first tunable laser action of a platelet semiconductor in an external cavity. We have achieved cw output powers of up to 9 mW from a CdS platelet optically pumped by an Ar+ laser at 476 nm. The energy conversion efficiency is 10% into the TEM00 mode. Tunability of the laser output was demonstrated from 495 to 501 nm using an intracavity prism with the crystal kept at a temperature of 95 K. Additional tuning to 504 nm was achieved by varying the temperature to 140 K.

Broadly tunable mode‐locked HgCdTe lasers

We report tunable cw mode‐locked laser action from synchronously pumped HgCdTe lasers. 4–8‐μm‐thick liquid phase expitaxial layers lasing at λ=1.2 and λ=1.73–2.0 μm are longitudinally pumped by a neodymium: yttrium aluminum garret (Nd:YAG) laser. Peak output powers of 50 W using a chopped pump beam, and a cw mode‐locked average output power of 5.6 mW, have been achieved at a wavelength of 1.2 μm. Nearly bandwidth‐limited pulses of 6‐ps duration have also been obtained. Tuning from λ=1.82 to 2.0 μm via the Burstein–Moss shift has been accomplished on a single epilayer by varying the loss in the external cavity.

Photon-counting statistics of pulsed light sources.

We report measurement of the photon-counting distributions of nanosecond-duration light pulses. Photon counting is performed on light sources with widely different photon statistics, such as (1) a Q-switched Nd:YAG-laserpumped dye laser operating well above threshold and producing single-mode nanosecond pulses, (2) the same laser operating close to threshold, and (3) a rotating ground-glass aberrator illuminated by the laser pulses of case (1). The method is particularly suitable for the investigation of the statistics of light generated by the nonlinear interaction of radiation with matter.

Dewar design for optically pumped semiconductor lasers

A liquid‐nitrogen Dewar has been constructed to allow precise and stable alignment of semiconductor platelets. Laser action in an external cavity is observed when the platelets are longitudinally pumped by an Ar+ laser. A microscope objective mounted inside the Dewar is used to focus both the pump and the semiconductor laser beam to a 5‐μm spot. The sample can be moved and tilted while being kept at a temperature of 85 K. Sample mounting techniques are also described.

Polariton‐induced compensation of pulse broadening in optical fibers

We report the first experimental technique for compensating the pulse broadening in single‐mode optical fibers, using the ’’slow’’ anomalous pulse propagation in the exciton‐polariton resonance in a direct‐gap semiconductor. Mode‐locked dye laser pulses of 0.7‐ps duration at 8180 A were propagated through a 100‐m single‐mode optical fiber and emerged with 2.8‐ps duration. We have demonstrated the compensation of this pulse broadening in optical fibers by passage through a 6.3‐μm‐thick GaAs crystal, taking advantage of the group velocity dispersion around the discrete n = 1 exciton‐polariton resonance.