Colliding-pulse Mode-locked Dye Laser Research Articles

18 fs Pulses-New Advance of CPM Dye Laser

Since the 1980s, colliding pulse mode-locked (CPM) ring dye laser has been themajor system to generate femtosecond light pulses owing to its reliability, stability andavailability in materials and equipment though Ti-sapphire laser has now demonstratedthe potential to produce short pulses. It has been reported that as short as 27 fs

Generation of synchronized femtosecond pulses independently tunable in the mid-infrared

The broad-band output of a femtosecond travelling wave dye laser and amplified pulses from a colliding-pulse mode-locked dye laser are mixed in LiIO 3 crystals to generate infrared pulses of subpicosecond duration. Two stable pulses independently tunable in the wavelength range from 2.5 to 5 μm are produced with a duration of 300 fs and a relative temporal jitter of less than 100 fs. Infrared energies of up to 10 nJ per pulse are achieved. First pump-probe experiments with lead salt semiconductors demonstrate the favorable properties of this novel infrared source.

Amplification of light pulses in the visible through stimulated Raman scattering

Pulses from a colliding pulse modelocked dye laser operating around 546 nm have been amplified within an optical fibre through stimulated Raman scattering in a counterpropagating configuration. Gain values of up to 25 dB have been achieved at a repetition rate of 1 kHz.

Picosecond optical correlation using dynamic holography in polyacetylene

An image-processing system based on four-wave mixing in a film of polyacetylene less than 100 nm thick is demonstrated with a 1-ps processing cycle time. Image phase conjugation and cross correlation are performed with a resolution space-bandwidth product of 0.68 x 10(5) (equivalent to 261 x 261 pixels) in the phase-conjugate image. The light source was amplified optical pulses from a colliding-pulse mode-locked dye laser at a wavelength of 625 nm.

Characterization and modeling of a femtosecond optical parametric oscillator suitable for tunable pump-probe spectroscopy

An improved cavity configuration continuous-wave mode-locked optical parametric oscillator (OPO) suitable for two-frequency femtosecond pump-probe spectroscopy is described. The OPO is based on intracavity pumping of a KTiOPO/sub 4/ (KTP) crystal in a colliding pulse mode-locked dye laser and produces femtosecond pulses at a 90 MHz repetition rate at average powers of 22 mW at 620 nm and 1-2 mW in the infrared. A model is synthesized from existing laser and parametric oscillator theories, and numerical simulations reproduce some qualitative aspects of the parametric oscillator's behavior. The theory accurately predicts the renormalization properties of the pump pulses in the presence of a nonlinear intracavity loss, and the existence of megahertz intensity oscillations on the output power envelope for excessively self-phase modulated pump pulses.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Tunable femtosecond pulses in the ultraviolet, generated by upconversion of a traveling-wave dye laser

We report the generation of 200-fs pulses with 300-nJ energy; the pulses are tunable in the UV spectral range. Amplified pulses from a colliding-pulse mode-locked dye laser at 620 nm and the output of a femtosecond traveling-wave dye laser (TWDL) are mixed in a nonlinear crystal. Wavelength tuning is achieved by changing the phase-matching angle, which results in upconversion of different spectral components of the broadband output of the dye laser. Approximately 15% of the photons from the TWDL are converted into the UV.

Noise characterization of a self-mode-locked Ti:sapphire laser

The phase and amplitude noise spectra of a self-mode-locked Ti:sapphire laser are measured and compared with the noise characteristics of a colliding-pulse mode-locked (CPM) dye laser. The timing jitter of the Ti:sapphire laser is found to be approximately half that of the CPM laser for jitter rates above 50 Hz. The amplitude noise of both lasers is comparable for frequencies of as much as several hundred kilohertz. However, between 0.5 and 5 MHz the noise spectrum of the Ti:sapphire laser is 126-134 dB below the carrier, while the CPM laser noise is limited by the pump laser at 115-131 dB below the carrier.

The role of amplitude and phase shaping in the dispersive-pulse regime of a passively mode-locked dye laser

The relative contributions of nonlinear amplitude and phase modulation in determining the shape and duration of a sub-100-fs pulse generated by a colliding-pulse mode-locked dye laser are examined. A phenomenological numerical model is developed that accounts consistently for the finite bandwidth of the saturable gain and absorbing media. The results for the model are compared with the experimentally measured amplitude and phase of 60-fs pulses from a laser operated in the dispersive (i.e., nonsoliton) regime. Good agreement is found with the measured pulse amplitude temporal asymmetry and with the measured chirp.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Reduction of phase noise in passively mode-locked lasers

The phase noise of a colliding-pulse mode-locked ring dye laser and a coupled-cavity mode-locked color-center laser has been reduced by up to two orders of magnitude in the 50-500 Hz range by referencing the cavity frequency of the optical resonators to that of an electronic oscillator. Using this technique a common reference is available to provide a direct electronic signal to the deflection electronics of a synchroscan streak camera so that real-time phase error detection can be achieved. >

Third-order dispersion in a passively mode-locked continuous-wave dye laser

The pulse duration tp of a colliding-pulse mode-locked dye laser is measured versus the intracavity third-order dispersion (TOD), where the group-velocity dispersion is optimized by a four-prism sequence. The intracavity TOD is varied by the addition of layers on quarter-wave dielectric-multilayer mirrors. The shortest pulse is observed at a nonzero TOD. The TOD dependence of tp is explained by a new model that describes the saturation of absorption and gain dyes in the frequency domain, with the assumption of a steady sech2-shaped pulse with weak chirp and a negligible fast self-phase modulation.

Theoretical analysis of pulse development in a colliding pulse mode-locked dye laser

The pulse development in colliding pulse mode-locked dye lasers is analysed theoretically. The chosen parameters belong to a c.w. argon laser pumped linear resonator arrangement with rhodamine 6G in ethylene glycol as gain medium and DODCI (3,3′-diethyloxadicarbocyanine iodide) in ethylene glycol as saturable absorber. The pulse shortening and pulse broadening effects in the laser oscillator are investigated. The steady-state pulse duration is determined by equal pulse broadening and pulse shortening within a single resonator round-trip. The detuning of the absorber jet out of the middle position of the resonator is considered. Multiple transits through the resonator are simulated to study the influence of various resonator and dye parameters on the pulse development and the background signal suppression. Fast relaxations within theS 1 andS 0-state of DODCI are necessary for sufficient background suppression to obtain femtosecond pulse trains.

Femtosecond pulses in the mid-infrared generated by downconversion of a traveling-wave dye laser

Amplified pulses from a colliding-pulse mode-locked dye laser at 620 nm and the output of a femtosecond traveling-wave dye cell are mixed in a LiIO(3) crystal to generate femtosecond pulses in the wavelength range near 5 microm. As much as 10% of the photons from the traveling-wave laser are converted to stable infrared pulses of less than 400-fs duration, 10-nJ energy, and 8-kHz repetition rate.

Pulse propagation near zero group-velocity dispersion in a femtosecond dye laser

The propagation of femtosecond pulses in a colliding-pulse mode-locked dye laser near zero group-velocity dispersion is studied. The pulse spectrum is shown to exhibit a double-peak structure. This structure and its dependence on the intracavity dispersion can be explained by nonlinear pulse propagation near zero dispersion. A value for the third-order dispersion of the laser cavity is deduced and is found to be predominant for pulses shorter than 50 fsec.

Buildup of steady-state subpicosecond and femtosecond pulses in a colliding-pulse mode-locked ring dye laser

We show for the first time, to our knowledge, that the buildup time to steady-state femtosecond pulses in a typical colliding-pulse mode-locked dye laser (lambda = 620 nm) with compensating prisms is 15 microsec after the pulses have been completely modulated. For a similar laser without the compensating prisms, the buildup time is 40 microsec and exhibits interesting oscillatory behavior in the initial stage.

Femtosecond spectroscopy of stimulated emission from highly excited dye molecules

Intense femtosecond pulses in ultaviolet and visible wavelengths are generated in an excimer-laser-pumped amplifier system with input pulses originating from a colliding-pulse mode-locked dye laser. The relaxation of high-lying singlet states in laser dyes is studied after ultraviolet excitation. Two time scales of relaxation are observed: (i) The intramolecular redistribution of energy occurs in rhodamine dyes with short time constants of ~200 fsec. (ii) The subsequent cooling of the vibrationally hot molecules on the picosecond time scale is monitored through the temperature-dependent broadening of the emission spectrum. Theoretical calculations of the emission spectrum of the hot molecules account well for the experimental results.

Application of Nonlinear Organic Materials to Femtosecond Light-Pulse Technology

Abstract Two experimental studies are presented illustrating applications of organic materials of high nonlinear refractive index to femtosecond light-pulse technology. One is intracavity pulse-compression of a colliding-pulse mode-locked dye laser with the addition of nonlinear organic materials into a saturable absorber solution. Another is femtosecond pulse compression external to the laser using nonlinear organic fibers. On the basis of the experimental results, the present problems and the optical properties that nonlinear organic materials should satisfy are discussed.

Third-order group-velocity dispersion in a colliding-pulse mode-locked dye laser

We present results obtained from a numerical simulation of a colliding-pulse mode-locked dye laser and study the influence of group-velocity dispersion on the pulse characteristics. It is found that positive third-order dispersion can help to shorten the pulse duration and to reduce the dependence of energy and pulse duration on pump power.

Continuous-wave mode-locked and dispersion-compensated femtosecond optical parametric oscillator

We describe dispersion compensation of a cw mode-locked optical parametric oscillator based on a thin crystal of KTiOPO4 pumped intracavity by a standard colliding-pulse mode-locked dye laser, The device provides potential cw tunability from 0.72 to 4.5 μm with milliwatt outputs. Transform-limited pulses should be possible throughout the tuning range;here we report pulse widths of 105 fsec at 840 nm and 108 Hz. Active stabilization of the oscillator cavity is also discussed.

Generation of tunable femtosecond pulses by traveling wave amplication

A simple system consisting of an amplified spontaneous emission source (ASE), a grating and a traveling wave (TW) amplifier which were pumped by the amplified output of a colliding-pulse mode-locked dye laser permits generation of continuously tunable femtosecond pulses. With three different dyes pulses shorter than 150 fs have been obtained between 660 nm and 785 nm. We have shown that the pulse duration of the amplifier output can be even shorter than the pump pulse. 23 fs pulses were generated at 700 nm by subsequent pulse compression in a fiber grating compressor.

Generation of 36-fsec pulses near 775 nm from a colliding-pulse passively mode-locked dye laser

We report the passive mode locking of a cw Rhodamine 700 dye laser using the saturable absorber DDI. Pulses as short as 36 fsec near 775 nm have been produced in a colliding-pulse mode-locked dye laser with adjustable intracavity group-velocity dispersion.