An investigation of the axial mode behaviour of a helical TEA-CO2 laser

The frequency behaviour of axial modes was investigated during the initial phase of mode competition in case of a helical TEA-CO₂ laser. With the help of a homodyne technique single-shot and multi-shot beat spectra were measured. Analysing these under various aspects and combining the results of an earlier investigation it was found that

1. inferior modes exist only for 100–200 ns.
2. their spectral width is less than 1 MHz and is determined by lifetime broadening, with the dominant mode narrower than 0.77 MHz,
3. in the average over many shots the spectral envelope of modes does not follow a Lorentzian shape as expected for the Lorentzian gain curve,
4. the beat powers change widely from shot to shot, whereas the total laser power remains constant,
5. no specific phase structures are likely to govern the laser emission, although the maximum emission principle appears to be obeyed with every individual shot. In an appendix relations are derived and summarized which are required for the evaluation of beat mode spectra and for the determination of line width as they apply to the actual time dependence of the laser emission.

     

Steady-state mode-locking operation in a laser with a saturable absorber

It is shown that a simple correspondence exists between the form of radiation for a steady-state mode-locking operation and the well-known solution of the one-mode problem. The dependence of the amplitude and shape of the pulses on the amount of absorber is determined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 2, pp. 221–226, February, 1972.     

Passive mode-locking of a diode-pumped Tm:GdLiF4 laser

We propose an optical near-field assisted sputtering method for repairing scratches on the surface of polycrystalline ceramics in a self-assembling manner. An Al₂O₃ source was sputtered on substrates with laser radiation of wavelength 473 nm. The average depth of the scratched grooves on polycrystalline Al₂O₃ ceramic substrate decreased from 3.2 nm to 0.79 nm. Using a Hough transform, we also confirmed the selective repair of scratches.     

The hybrid mode-locking of a cw Rhodamine 700 dye laser

Two saturable absorber dye solutions, HITCI and DOTCI, have been employed to provide hybrid mode-locking of a cw dye -aser operating over the 770–781 nm and 710–718 nm spectral ranges respectively. Pulses as short as 0.55 ps and 0.47 ps were obtained in these respective regions.     

Toward higher-order passive harmonic mode-locking of a soliton fiber laser

We report >13 MHz/mW pump power efficiency in increasing the repetition rate of passive harmonic mode-locking by engineering the soliton pulse energy in Er fiber lasers incorporating carbon nanotube saturable absorber. Stable pulses with a ～5 GHz repetition rate and 40 dB of super-mode suppression are demonstrated with only ～400 mW pump power in a single-clad fiber laser.     

Cascaded mode-locking of a spectrally controlled Yb:KYW laser

Self-starting and stable mode-locking of an Yb:KYW laser in the picoseconds pulse regime has been achieved by exploiting a positive cascaded Kerr lens in periodically poled KTP. The use of a volume Bragg grating (VBG), for locking the output spectrum of the laser, was essential to achieve a stable mode-locked operation in this wide gain bandwidth laser material. The laser emitted stable, nearly transform-limited pulses with a duration of 16 ps, at a repetition rate of 210 MHz, and with an energy of 3.2 nJ. The mode-locked spectrum was centred at 1,029.1 nm and featured a FWHM bandwidth of 85 pm, which was effectively determined by the VBG. Combination of a large cascaded Kerr nonlinearity with spectral limiting by a VBG represents so far the best opportunity for stable mode-locking of a broadband laser to produce near-transform-limited picosecond pulses.     

Kerr-lens mode-locking of Nd:glass laser

We report what is to our best knowledge the first Kerr-lens mode-locking of a Nd:silicate glass laser. Pulses as short as 64 fs were generated. For a broadband inhomogeneously broadened laser, the formation of the soliton-like pulses requires a minimum amount of negative group velocity dispersion (GVD), and more negative GVD is needed to have stable, self-sustained mode locking.     

A one joule,XeCl pumped dye laser

A 4 J XeCl (308 nm) laser has been used to produce 1 J of dye laser output from selected dyes whose lasing wavelengths sample the spectral range from 330 to 600 nm.     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

 利用光学金相显微镜对TEA-CO₂脉冲强激光辐照的Hg_0.8Cd_0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J，能量密度为937.5 J/cm²的强激光辐照下，晶片表面呈现出熔融迹象和大量的微裂纹，微裂纹密度从激光辐照区中心向外逐渐减少，裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加，晶片表面熔融更加剧烈，裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

Electronic frequency tuning of the acousto-optic mode-locking device of a laser

The effect of the electronic tuning of the acoustic resonances in an acousto-optic mode-locking device of a laser is investigated theoretically and experimentally. The problem of the excitation of a Fabry–Perot acoustic resonator by a plate-like piezoelectric transducer (PET) is solved in the approximation of plane acoustic waves taking into consideration the actual parameters of an RF generator and the elements for matching the PET to the generator. Resonances are tuned by changing the matching inductance that was connected in parallel to the transducer of the acousto-optic cell. The cell used in the experiment was manufactured from fused silica and included a lithium niobate PET. Changes in the matching inductance in the range of 0.025 to 0.2 μH provided the acoustic-resonance frequency tuning by 0.19 MHz, which exceeds the acoustic- resonance half-width.     

Investigation of kerr-lens mode-locking of a flashlamp-pumped Nd:YAG laser

In this paper, we report that mode-locked operation is realized in a flashlamp-pumped Nd:YAG laser with a nearly critical stable resonator, using LiF:F₂⁻ color center crystal as a modulation device. A single pulse train with the energy of 25 mJ and the pulse duration of 82 ps is obtained. Both the theoretical and experimental results have shown that the mode-locked operation has resulted from kerr-lens effect formed in combination with self-focusing within Nd:YAG and an aperture at a specific point, but not directly from the saturable absorption of LiF:F₂⁻ crystal.     

Saturable absorber mode-locking and laser pulse compression

The theoretical predictions of two alternative models of saturable absorber mode-locking in dye lasers are compared. The predicted mode-locking and pulse compression regimes are considered for both flashlamp-pumped and cw dye lasers, and some questions raised thereby are tested by numerical simulation of pulse propagation.     

Nd：YAG激光器中的自锁模

本文报道在Nd:YAG激光器中首次获得的自锁模脉冲序列.自锁模是由于Nd:YAG棒中的自相位调制引起的.在主被动对撞锁模运转情况下,自锁模对脉冲波形有较大的影响.     

脉冲强激光破坏Hg0.8Cd0.2Te晶片材料的机理分析

利用光学金相显微镜对TEA-CO2脉冲强激光辐照的Hg0.8Cd0.2Te晶片表面进行了观察。在单脉冲能量为37.5 J,能量密度为937.5 J/cm2的强激光辐照下,晶片表面呈现出熔融迹象和大量的微裂纹,微裂纹密度从激光辐照区中心向外逐渐减少,裂纹沿晶体的(111)面扩展。随着脉冲连续作用次数的增加,晶片表面熔融更加剧烈,裂纹数目、裂纹深度和宽度都有所增加。分析认为：HgCdTe晶片的破坏与激光辐照能量、脉冲连续作用次数、激光场强分布、激光热应力、激光支持的燃烧波和物质的蒸发波等冲击波有关。     

Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS_2 as a saturable absorber

Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible Mo S2SA. The 20 th harmonic modelocked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio(SMSR) of 36.1dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.     

A fiber-ring laser incorporating dual mode-locking mechanism

A fiber-ring laser incorporating dual mode-locking mechanisms is presented and demonstrated. A multi-quantum well (MQW) semiconductor optical amplifier (SOA) acts as active loss modulator, because the external optical signal injection results in gain depletion. In addition, a reflective SOA (RSOA) and a polarization beam splitter (PBS) introduce nonlinear polarization rotation (NPR), and also function as a saturable absorber. With this dual mode-locking mechanism, 10 GHz repetition-rate stable pulses, with pulse width of 16 ps and a root-mean-square timing jitter of 1 ps, was obtained without the use of external compression approaches.     

Passive mode-locking of the Yb:CNGG laser

Passive mode-locking using a SESAM is demonstrated for the Yb-doped cubic non-stoichiometric crystal CNGG which exhibits local disorder. The pulse duration of 73 fs obtained is the shortest for an isotropic Yb-doped laser crystal while larger output coupling resulted in average output powers of 750 mW with 66% efficiency in the mode-locked regime.     

Passive harmonic mode-locking in a fiber laser with nonlinear polarization rotation

On basis of numerical simulation and analytical treatment, we investigate the multiple pulse passive mode-locking of a fiber laser with nonlinear loss due to the nonlinear polarization rotation technique. Various additional mechanisms resulting in the ordering of ultrashort pulses inside the laser resonator and in the realization of harmonic passive mode-locking are analyzed. Among which are the active harmonic modulation of the intracavity loss or of the refractive index, the passive modulation of the index due to the inertial properties of intracavity elements, and the amplification modulation due to the depletion and the relaxation of the gain. The velocity of pulses relative to each other is determined, it results in attractive or repulsive pulse-pulse interaction, and allows to evaluate the conditions of ordering of the pulses inside the cavity.     

On the possibility of mode-locking a dye laser by a fast saturable absorber

The problem of mode-locking a fully relaxing saturable (dye) laser medium by an instantaneously saturating (fast) absorber is theoretically considered when group velocity dispersion and Kerr-type nonlinearity are present. Off-resonant chirped solutions are found whose minimum duration is determined by the relative losses (saturable and nonsaturable) and by the saturation depth of the absorber. The addition of nonlinear elements can only broaden the stability range of the solution with respect to the group velocity dispersion.