Systematic evaluation and prediction of the pulse width of synchronously pumped lasers

Received: 17 March 1997/Revised version: 21 July 1997     

Subpicosecond pulse generation in synchronously pumped and hybrid ring dye lasers

Subpicosecond pulse generation has been examined in synchronously pumped mode-locked ring dye laser systems. These include hybrid and composite absorber/gain media arrangements as well as a simple synchronous cavity. The shortest pulses recorded were 0.3 ps for the hybrid system, and this has been shown to be critically dependent on the positioning of the absorber jet in the centre of the cavity to better than 50 m. Stable operation for subpicosecond pulse generation has been achieved in the ring configuration with greater wavelength tunability and higher average power conversion efficiency than with conventional cavity arrangements.     

Pulse formation in synchronously pumped infrared dye lasers

Pulse formation in synchronously pumped dye lasers with fast relaxing dyes is treated by computer simulation. The influence of spontaneous emission and chirp, as well as cavity mismatch, on the pulse characteristics and stability of generation are discussed.     

Theory of the synchronously pumped picosecond dye laser

The circulation of a synchronously mode locked dye laser pulse in a linear cavity configuration containing a dye cell as an active medium and a bandwidth-limiting element is treated. The condition that the pulse shape reproduces after each cavity round-trip provides a nonlinear integro-differential equation for the steady-state pulse shape. For the solution of this equation an approximate method, not limited to small pulse energies, is given and the pulse duration, intensity, energy, asymmetry of the pulse shape, stable regions and other interesting parameters are discussed.     

Numerical analysis of pulse generation in synchronously mode-locked cw dye lasers

We present theoretical results on the characteristics of pulses generated by a synchronously pumped dye laser. Our analysis indicates the important influence of spontaneous emission on shape and frequency chirp of the pulse. Dye-laser operation is possible within a wide range of cavity mismatch. A large mismatch of the lengths of the dye and the pump-laser cavity results in the generation of noise bursts caused by the influence of spontaneous emission. At small cavity mismatch pulse profile and frequency chirp of the pulse are directly generated in the steady-state regime by algebraic equations. Our formulas indicate that the sign of the pulse chirp depends only on the sign of the shift between laser frequency and centre frequency of the amplifying transition.     

Analysis of pulse parameters in synchronously pumped infrared dye lasers

Equations describing steady-state pulses circulating in synchronously pumped dye lasers with dyes of arbitrary fluorescence lifetime are derived and solved by numerical methods. Special attention is devoted to infrared emitting dyes characterized by short fluorescence lifetimes in the order of 10 ps. The results are compared with the case of slow dyes typically used in the visible spectral region.     

Subpicosecond pulse generation in synchronously pumped energy transfer dye lasers

We describe a laser-cooling experiment on Mg⁺ ions confined in an electromagnetic trap (Penning trap or rf trap) and give the preliminary experimental results. In particular, we have observed a laser cooling in the Penning trap configuration in which a measured temperature of about 1 K has been obtained.     

Theory of synchronously pumped dye lasers

An analysis of cw synchronously pumped dye lasers is presented. Under the assumption that the cavity (tuning element) bandwidth is much wider than the bandwidth of the transform limited pulses generated, the pulse forming dynamics is rigorously treated. It is shown that for a finite mismatch between the lengths of the dye and the pump lasers, a steady-state pulse develops in the dye laser cavity with a conserved pulseshape. The characteristics (energy, shape, peak power, duration) of these pulses of ultimate width are quantitatively determined as a function of cavity mismatch. An analytical solution for the pulse envelope is determined, which yieldsI(t)∝Sech²(t/t _p ) to a good approximation.     

Picosecond and subpicosecon pulse generation in synchronously pumped mode-locked cw dye lasers

Generation of tunable near-infrared picosecond and subpicosecond pulses in a synchronously pumped cw mode-locked Oxazine-1-perchlorate dye laser has been investigated for different values of the important system parameters. The experimental results confirm the predictions of a simple theoretical model which describes the steady-state pulse duration in terms of gain modulation strength, pump power, intracavity bandwidth, pump pulse length and cavity detuning. For a pump-pulse length of 100 ps and a bandwidth of more than 500 Å for the intracavity tuning element dye-laser pulses as short as 0.35 ps have been obtained. Under these conditions up to 100 mW of average output power were provided. In addition, mode-locking of an Oxazine 750 dye laser by synchronous pumping with the cw train of pulses obtained from the Oxazine-1-Perchlorate laser is reported.     

Phase-modulation effects in synchronously pumped dye lasers

We report the numerical calculation of pulse generation in SPDL including phase-modulation effects due to gain saturation. The steady-state pulses are strongly down-chirped at the leading edge if the laser frequency is detuned from the line centre of the amplifying dye. The pulse duration is found to be almost independent of wavelength detuning.     

On the performance of short pulse Nd3+:LSB microchip lasers

Experimental results from studies of the laser characteristics of Nd:LSB crystals in both cw and passive Q-switching arrangements are presented. The dependence of the main laser parameters on the output coupling and saturable absorber transmission for two doping levels of Nd was investigated. It is demonstrated that due to its high absorption, low losses and intrinsic strong thermal lensing, even at pump powers of less than 200 mW, the Nd:LSB has excellent properties in terms of efficiency, beam quality and pulse duration. In addition, it exhibits high pulse-to-pulse and pulse width versus pump power stability. Received: 11 June 2001 / Revised version: 30 July 2001 / Published online: 15 October 2001     

The transient regime of synchronously pumped picosecond dye lasers

Using a four-level model of the active medium, ultrashort pulse generation in the synchronously-pumped dye laser is investigated theoretically. Particular attention is paid to the transient regime in which the pump pulse train is relatively short. On the basis of these calculations a stable generator of tunable bandwidth-limited picosecond pulses was optimized.     

Application of the opto-acoustic effect to the operation of optically pumped far-infrared gas lasers

A method is reported which allows the operation of optically pumped farinfrared (FIR) gas lasers in a simple way: A spectrophone is used to control and to stabilize the pump laser frequency in order to achieve most efficient optical pumping of the FIR laser gas.     

Synchronized picosecond pulse generation with a synchronously pumped dye laser and a compressed Nd: YAG laser for non-degenerate transient grating experiments

We have set up a laser system which simultaneously provides synchronized picosecond pulses in the visible and at a wavelength of 1.06 m with a repetition rate of 76 MHz. The set-up consists of a dye laser synchronously pumped by the second harmonic of a cw mode-locked Nd:YAG laser and a fiber-grating compressor for the fundamental wavelength of the Nd;YAG laser. Crosscorrelation measurments reveal the time jitter between the two pulse trains to be less than 10 ps. As a first application we have performed non-degenerate transient grating experiments in semiconductors. The non-degenerate technique allows to use excitation energies well above the bandgap energy and to separate non-linear refractive index effects from photoinduced absorption or transmission changes.     

Infrared recombination lasers pumped by low energy Nd: YAG and excimer lasers

24 infrared laser lines on atomic and ionic transitions have been observed in recombining plasmas by vaporizing and ionizing Cd, Pb, Sn, Zn, and Mg with low energy Nd:YAG or excimer pump-lasers. For operation and optimization of the recombination lasers separated plasma spots and a plasma confinement have been used. The operation of shorter wavelength systems by isoelectronic scaling is discussed.     

Continuous wave diode pumped Yb:LLF and Yb:NYF lasers

Experimental and theoretical results of investigation of CW Yb:LiLuF₄ (Yb:LLF) and Yb:Na₄Y₆F₂₂ (Yb:NYF) lasers under longitudinal diode laser pump are reported. Slope efficiencies of 41%, 58% with 0.21, 0.53 W of output powers were obtained for the Yb:LLF and Yb:NYF lasers, correspondingly. The Yb:NYF laser demonstrated tunability in the region from 1005 to 1061 nm. The mathematical modelling of CW laser operation predicts under optimized laser parameters optical to optical efficiencies of about 55% and 51% for Yb:LLF and Yb:NYF lasers, respectively.     

Q-switched Nd lasers pumped directly into the F3/2 emitting level

The influence of the direct pumping into the ⁴F_3/2 emitting level on the output characteristics of continuous-wave (CW) pumped, passively or actively (acoustooptic, AO) Q-switched Nd lasers is discussed. In case of passive Q-switching by Cr⁴⁺:YAG saturable absorber (SA) crystal, the change of pumping wavelength from 0.81 μm into the highly-absorbing ⁴F_5/2 level to 0.88 μm into the ⁴F_3/2 level of Nd does not modify the energy of the Q-switch pulse, but increases the pulse repetition rate and the laser average power for the same absorbed pump power. This is demonstrated with 0.81 and 0.88 μm CW laser diode-pumped Nd:YAG and Nd-vanadate lasers with average output power in the watt-level range at 1.06 μm. The effect is explained by the control of passive Q-switching by the intracavity photon flux that is influenced by the pump wavelength and by the initial transmission of the SA crystal. On the other hand, it is discussed and experimentally proved that due to the possibility to control externally the frequency of switching, in case of the AO Q-switched Nd laser the change of the pump wavelength from 0.81 to 0.88 μm increases the pulse energy for a fixed frequency, leading to a corresponding increase of the average laser power.     

On noise and fluctuations in a synchronously mode-locked cw laser system

A single-shot and synchronously-scanned streak camera, autocorrelation and noise spectrum analysing techniques are utilized to study the output characteristics of synchronously mode-locked cw lasers. Four main conclusions are drawn: (i) the pulse train from a synchronously-pumped dye laser reveals, besides phase jitter, considerable pulse shape fluctuations; (ii) autocorrelation measurements may be highly misleading when actual pulse shapes are considered; (iii) both the phase jitter and pulse shape fluctuations of the dye laser output are caused by the phase fluctuations of the pumping ion laser pulse train; (iv) the phase jitter of the ion laser proceeds from the fluctuations in the cavity roundtrip time with a characteristic time of about 5 s. Under optimum conditions the rms noise of the dye laser output was 2% and the phase jitter with respect to the rf sine drive of the acousto-optical mode-locker, 30 ps. A qualitative explanation fo the noise properties is given.     

On the possibility of using lasers as detectors of gravitational waves

The possibility to use narrow optical resonances and highly stable lasers as detectors of gravitational waves are discussed. The methods for measuring small displacements are based on the registration of small variations of a radiation frequency that arise in changing an optical phase. First results on the use of narrow resonances for precision measurements of small displacements are given. The achieved absolute sensitivity of the measurements amounted to 6·10^?6 Å on the basis of 5·10² cm.