R. K. Jain

Subpicosecond pulses from a tunable cw mode‐locked dye laser

Tunable subpicosecond pulses (pulse width =0.8 psec) have been obtained from a cw mode‐locked Rhodamine B dye laser. Mode locking is achieved by synchronous pumping of the Rh‐B dye with a cw train of pulses which are obtained from a synchronously mode‐locked Rhodamine 6G dye laser.

Generation of synchronized cw trains of picosecond pulses at two independently tunable wavelengths

We report the generation of synchronized trains of picosecond pulses at two independently tunable wavelengths from cw mode‐locked dye lasers, synchronously pumped by a mode‐locked argon‐ion laser (pulse width∼100 psec). This has been achieved both by two‐wavelength operation of a single Rhodamine 6G dye laer and by synchronously pumping two independent (Rh‐6G) dye lasers. For both cases, with typical pulse widths of ≈ 5 psec at two independently tunable wavelengths, cross‐correlation measurements indicate good synchronization, with a jitter of less than ∼10 psec between the two pulse trains.

A time‐dispersion‐tuned fiber Raman oscillator

By using a novel time‐dispersion‐tuning scheme a fiber Raman oscillator pumped by a mode‐locked argon laser has been tuned within the broad Raman gain bandwidth (∼400 cm−1) of silica glass by varying the resonator length. A tuning range of 40 A in the green is obtained with an average pump power of 1.6 W. A combination of time dispersion and prism tuning extends this range to 134 A (5153–5287 A). Tunable Raman oscillation with lower threshold in the 1‐μ region should be possible with a mode‐locked Nd : YAG laser pump.

A high‐efficiency tunable cw Raman oscillator

Continuously tunable cw Raman oscillation has been achieved in the visible by pumping a single‐mode fused silica fiber with several lines from an argon ion laser. The 100‐m‐long fiber has a core diameter of 3.3 μm and a loss of 17 dB/km at 5145 A. Threshold was achieved with ∼1.0 W of pump power in the fiber. With 4 W of 5145‐A power coupled into the fiber, the Raman oscillator was prism tuned over 80 A. Typical linewidths were ∼2 A. At 5280 A, net input to output power conversion efficiencies of ∼9% and pump depletion of over 80% have been achieved. The simplicity, efficiency, and broadband tunability of fiber Raman oscillators both in the visible and in the near infrared make them potential rivals to other coherent sources of tunable radiation, such as dye lasers and parametric oscillators.

Pulse‐width dependence on intracavity bandwidth in synchronously mode‐locked cw dye lasers

We present a model of the synchronously mode‐locked cw dye laser which predicts a square root dependence of dye pulse width on pump pulse width and intracavity bandwidth (ωc). Experiments performed on the Rhodamine 6G laser confirm the ω−1/2c dependence. For a pump pulse width of 100 ps, subpicosecond dye pulses are obtained for intracavity bandwidths greater than 150 A, and the minimum pulse width is shown to be limited by the bandwidth of the dye to ∼0.5 ps.

A tunable multiple Stokes cw fiber Raman oscillator

A broadly tunable source of coherent cw radiation has been achieved by the use of a multiresonant cavity for multiple Stokes oscillation in a fused‐silica fiber Raman oscillator. Each order of tunable Stokes emission acts as a pump for the next higher order; a net tunability of several times the intrinsic Raman gain bandwidth is obtained. With 8 W of 5145‐A pump radiation coupled into a 100‐m‐long single‐mode fiber, four orders of Stokes oscillation have been obtained, yielding over 350 A of tuning in the 5200–5660‐A spectral range.

Subpicosecond pulse generation in a synchronously mode-locked cw rhodamine 6G dye laser

We report the generation of wavelength-tunable subpicosecond pulses in a synchronously mode-locked rhodamine 6G dye laser, pumped directly by a mode-locked argon-ion laser (pulsewidth approximately 100 psec). The nearly transform-limited subpicosecond pulses are tunable in the 5625-to 6045-A spectral range. Peak powers of approximately 1 kW have been obtained.

Stable room‐temperature light emission from metal‐insulator‐metal junctions

Stable room‐temperature light emission has been observed from planar Mg‐MgO‐Ag junctions. The light emission is presumably due to roughness‐induced radative decay of surface plasma modes excited by tunneling electrons. Roughening of the planar tunnel structure is obtained by growth of a plateletlike structure during slow evaporation of the Mg film.

Group velocity matching in optical fibers.

Group velocity matching has been observed in an optical fiber. The matching occurred in a fiber Raman oscillator pumped by mode-locked laser pulses. The group velocity difference between pump and Stokes pulses due to material dispersion was compensated for by the group delay between two different waveguide modes.

Characteristics of high‐field preionized discharges for transversely excited waveguide lasers

We have investigated the role of the preionization cathode material and the preionization energy in high‐field preionized discharges of a CO2 laser mixture at atmospheric pressure. Independent control of both the E/p and the input energy is demonstrated over a large range of values. These results are applicable to the design of waveguide lasers and other types of gas‐discharge devices.