Experimental method for the measurement of hyperfine transition saturation intensities in a gaseous medium

A laser system capable of generating picosecond pulses of 2 ps duration and peak powers of up to 50 MW, tunable throughout the emission spectrum of the lasing medium is described. The system consists of a cw dye laser which is tuned and is actively mode-locked by means of a novel interferometer. Single-pulse amplification is achieved via a two-stage N₂-laser-pumped amplifier arrangement. One of the most attractive features of the system here described is its inherent versatile broad tunability, which should allow, with different lasing media and pump sources, ps pulse generation from 400 to 700 nm using the same interferometer device.     

Significance of intra-cavity power density in synchronous mode-locking of CW-dye lasers

It is shown that there is a well-defined relation between the intra-cavity power density and the temporal structure of ultrashort light pulses generated by a synchronously pumped cw dye laser. To obtain pulses of good quality with high output power the beam cross-section in the lasing medium must be large, because the best performance is achieved at low power density.     

Experimental study of a semiconductor laser diode having a Mach–Zehnder interferometer in the cavity

The performance of a semiconductor laser diode that has an asymmetric Mach–Zehnder interferometer all-optical switch in the cavity has been studied experimentally. This novel device was designed to be free from clock pulse insertion, since mode-locked optical pulses are generated internally and change the balance of the interferometer periodically. The device was fabricated using a InGaAsP/InP buried heterostructure and the primary optical properties of the device were investigated. Lasing characteristics that were peculiar to the twin-cavity structure were observed, i.e., continuous-wave lasing power oscillation in relation to the injection current balance between the two arms, and cyclic changes in the single/multiple emission peaks as a function of bias voltage at the saturable absorber. Electrical spectrum analysis indicated 40 GHz modulation of lasing output from the twin-cavity laser.     

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.     

Production of 300W,nanosecond, transform limited optical pulses

Intense nanosecond pulses have been produced from a cw dye laser using a dye amplifier pumped by 6 ns nitrogen laser pulses. The pulses have a transform limited spectrum and are convenient for coherent propagation experiments.     

Diode-pumped, high-average-power femtosecond Cr3+ :LiCAF laser

We demonstrate a high-average-power continuous wave (cw) and cw mode-locked Cr3+ :LiCAF laser pumped by broad-area laser diodes. In cw lasing experiments, up to 580 mW of output was obtained with 4.35 W of incident pump. A semiconductor saturable absorber mirror was used to initiate stable, self-starting, mode locking. In the cw mode-locked regime, the Cr3+ :LiCAF laser produced nearly transform-limited, 67 fs long pulses near 800 nm with an average output power of 300 mW. The pulse repetition rate was 120 MHz, with a pulse energy of 2.5 nJ.     

Fluctuations in synchronously mode-locked dye lasers

We present detailed experimental data on random fluctuations of the pulse properties of a cw rhodamine 6G dye laser synchronously pumped by an acousto-optically mode-locked argon ion laser. It is shown that quantitative information about the fluctuations of the energy, the pulse repetition time and the duration of the pulses can be obtained from the power spectrum of the laser intensity which is measured with the use of an electronic spectrum analyser. This method is capable of revealing small, subpicosecond temporal pulse jitter. We show that the dye laser pulses exhibit an absolute r.m.s. jitter of 20 ps which is induced by the pump laser. The relative jitter in a dual system can be less than 1 ps because well defined correlations of the output fluctuations exist when two lasers are pumped by a common source.     

Generation of pulses shorter than 70 fs with a synchronously-pumped CW dye laser

Pulses shorter than 70 fs are generated with a synchronously-pumped cw dye laser using a dye medium composed of a mixture of rhodamine 6G and a fast recovery saturable absorber, DQOCI. The laser pulses exhibit no satellites. A stable output of 30 mW is obtained for only 300 mW of pump power.     

Simple picosecond dye laser system pumped by a frequency doubled,optically compressed Q-switched mode-locked Nd:YAG laser

Using the frequency doubled output of the 3 ps pulses from a temporally compressed cw Q-switched and mode-locked Nd:YAG laser, a simple synchronously pumped dye laser was constructed to give frequency tunable operation with short pulses in the 5–10 ps range and peak powers of ～ 15 kW. A circularly scanning streak camera operating in stroboscopic mode was also used to examine pulse formation in the dye laser.     

Frequency-modulation-mode-locked optical parametric oscillator

We demonstrate a novel technique for the generation of mode-locked pulses from a continuous-wave (cw) optical parametric oscillator (OPO). The technique is based on the deployment of a phase modulator in combination with an antiresonant ring interferometer internal to a cw OPO, simultaneously providing spectral broadening and phase-to-amplitude feedback modulation. The scheme is implemented in a doubly-resonant cw OPO based on MgO:sPPLT, configured in a standing-wave cavity and pumped at 532 nm. With the phase modulator activated and the cavity length synchronized, a stable train of 800 ps pulses is generated at a repetition rate of 160 MHz. Using single-pass second harmonic generation (SHG) of the OPO output, we observe a four times enhancement in SHG compared with cw operation, confirming the real achievement of energy concentration as a result of mode-locked operation.     

Recent developments in picosecond photochronoscopy

Recent developments in the techniques of generation and measurement of picosecond and sub-picosecond pulses from mode-locked lasers are reviewed. Particular attention is paid to frequency tunable, bandwidth-limited pulses from dye lasers, especially the cw dye laser. In measurement the main emphasis is put on the rapid advances of the last few years in ultra-fast streak-cameras, ans the recent developments in streak-camera synchronization to a cw mode-locked laser is described. Future prospects for shorter wavelenght pulses in the uv and vuv are briefly considered.     

Pulse structure studies and absolute cavity length determination for a synchronously pumped picosecond dye laser

Second harmonic cross correlation functions of a pulse with its near neighbor have been studied in a synchronously pumped cw dye laser. Measurements were made both as a function of dye laser cavity length mismatch and the number of cavity round trips separating the correlated pulses. The pulse envelope is found to have a characteristic interpulse frequency determined by the pump laser, whereas the pulse substructure has a characteristic frequency determined by the dye laser cavity length. The cross correlation measurements allow experimental determination of the dye laser length corresponding to exact synchrony. In contrast to theoretical predictions the length of exact synchrony corresponds to optimum pulse shape and duration. Our results are discussed in terms of a simple model which leads to pulse duration estimates as much as twice those obtained by conventional analysis of autocorrelation traces.     

Modulation instability induced by cross-phase modulation in a dual-wavelength dispersion-managed soliton fiber ring laser

We report on the observation of the modulation instability induced by cross-phase modulation in a dual-wavelength operation dispersion-managed soliton fiber ring laser with net negative cavity dispersion. The passively mode-locked operation is achieved by using a nonlinear polarization rotation technique. A new type of dual-wavelength operation, where one is femtosecond pulse and the other is picosecond pulse operation, is obtained by properly rotating the polarization controllers. When the dual-wavelength pulses are simultaneously circulating in the laser ring cavity, a series of stable modulation sidebands appears in the picosecond pulse spectrum at longer wavelength with lower peak power due to modulation instability induced by cross-phase modulation between the two lasing wavelengths. Moreover, the intensities and wavelength shifts of the modulation sidebands can be tuned by varying the power of the femtosecond pulse or the lasing central wavelengths of the dual-wavelength pulses. The theoretical analysis of the modulation instability induced by cross-phase modulation in our fiber laser is also presented.     

Nitrogen laser excitation of polymethine dyes for emission wavelengths up to 9500 Å

We have pumped polymethine dyes with a nitrogen laser and achieved tunable infrared stimulated emission up to a wavelength of 9500 Å. The dye laser output decreases during operation due to destruction of lasing molecules; this is measured as a function of the number of exciting laser pulses.     

Powerful dye laser oscillator-amplifier system for high resolution and coherent pulse spectroscopy

A peak power output of 100 kW in the visible at a linewidth as low as 60 MHz has been generated by using a cw dye laser oscillator followed by three single pass dye amplifier stages (or one double pass stage and one single pass stage), pumped by a single 1 MW nitrogen laser. The very high output power obtained in this laser system may be used to produce coherent ultraviolet pulses by sum or second harmonic generation in non-linear crystals or by third order mixing in atomic vapor.     

A long-pulse xenon ion laser as a pumping source for dye lasers

A simple xenon ion laser that is either sealed or has a gas flow mode is described. The laser delivered long pulses ( 15 μs) of almost 1 kW peak power. It has been used to pump a dye laser employing the same configuration as cw dye lasers. The system is inexpensive and can be mode-locked, enabling it to yield ultrashort pulses comparable in duration to those delivered by cw argon laser-pumped dye lasers but with much higher peak powers.     

Switching of the generation of nano/picosecond pulses in Nd:YAG laser with Pockels Q-switch

A method for switching the regime of single-frequency generation of nanosecond pulses to a train of picosecond pulses in the Nd:YAG laser with an electro-optic Pockels Q-switch without changing cavity elements is proposed. The single-frequency regime was provided by aligning an active element which played the role of a longitudinal cavity mode selector. The lasing spectrum was measured using a Fabry-Perot interferometer with simultaneous recording of pulse oscillograms.     

Solid-state dye lasers based on polymethyl methacrylate doped with pyrromethene 650

Solid-state dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of the dye PM650 were prepared. With SHG of Q-switched Nd:YAG laser (532 nm, ∼15 ns) pumping the samples longitudinally, the fluorescence, lasing spectra and slope efficiencies of the samples were obtained. The highest slope efficiency 27.49% and laser output energy 22.0 mJ was achieved in the sample with a dye concentration of 2.0 × 10⁻⁴ mol/L. To our knowledge, the results are the best under the same condition so far. The maxima of output lasing spectrum is about 653.5 nm. Our results have shown that using solid-state samples doped with PM650 can extend the dye laser wavelength to the red.     

小宽带堆积啁啾脉冲传输放大特性

 采用啁啾脉冲堆积的方法可获得ns量级宽带整形激光脉冲,对堆积啁啾脉冲时间波形的影响因素及传输放大后脉冲波形与光谱形状的特性进行了研究。结果表明：在传输过程中脉冲的演化规律与窄带脉冲的演化规律基本一致,而且传输放大过程也不会改变脉冲的调制结构,但光谱形状在传输放大过程中发生了变化,初步认为是由非线性效应造成的;小宽带堆积啁啾脉冲具有与窄带脉冲基本一致的的增益水平。     

A new family of lasing dyes from an old family of fluors

We report the development of a new series of laser dyes and describe the performance of these materials. This work was spurred by the realization that few laser dyes have an optimally shaped fluorescence emission for lasing action. Most of the dipole strength of the transition is concentrated in the 0.0 band, where lasing cannot occur, and very little is concentrated in the vibrational satellites 0–1 and 0–2 where lasing is possible. The new dyes are unsymmetrical materials which may be considered as a hybrid of a rhodamine molecule and a fluorescein molecule (fig. 1), and we consider them to be cyclized merocyanines. One dye in particular, 6-dimethylamino-9-o-carboxyphenylxanthen-3H-one (labelled SNH-8), has given power output and time stability better than the preferred lasing dye Rhodamine 6G. The effects of dye structure and of acid-base transitions on lasing activity will be discussed briefly. The theory of band-shaping and the detailed optical parameters of the new dyes will be presented separately.