All-solid-state diode-pumped Cr:LiSAF femtosecond oscillator and regenerative amplifier

3+ :LiSrAlF₆ (Cr:LiSAF) regenerative amplifier, seeded by a diode-pumped Cr:LiSAF femtosecond oscillator. The amplifier produced pulses of less than 200 fs duration and greater than 1 μJ energy at repetition rates of up to 25 kHz. Received: 27 February 1997/Revised version: 16 April 1997     

Intracavity frequency-tripling of actively mode-locked diode-pumped Nd:YAG laser

We report the first diode-pumped solid-state laser operating in cw-mode-locked regime and simultaneously achieving intracavity frequency-tripling. This laser provide UV picosecond pulses (λ=355 nm) of 10 ps duration with 0.5 mW average power at 150 MHz repetition rate. A different set of adjustments gave rise to a Q-switched mode-locked regime. Trains of hundred UV pulses of 60 ps duration and 4 W peak power were produced in this latter case at 50 kHz repetition rate. Received: 12 October 1998 / Revised version: 12 December 1998 / Published online: 26 May 1999     

High-energy picosecond Nd:YVO4 slab amplifier for OPCPA pumping

We demonstrate 12-ps pulses with up to 0.6-mJ pulse energy at repetition rates of 50 kHz and 100 kHz from a Nd:YVO₄ slab amplifier built in a simple four-pass configuration. Excellent noise performance with pulse energy fluctuations below 0.8% rms has been achieved by using 10-μJ seed pulses from a highly stable industrial laser system and moderate gain (30–46) in the slab amplifier.     

皮秒光纤激光脉冲两个关键问题的研究

窄带耗散孤子锁模光纤激光器可以产生接近变换限制的皮秒脉冲，但受非线性相移的限制，输出脉冲重复频率不能通过增加腔长来降低，脉冲能量仅在0.1 nJ以下，严重制约着这类皮秒脉冲的实际应用。提出一种通过耦合器抽取腔内脉冲能量、抑制腔内非线性相移积累，进而允许增加腔长来降低窄带耗散孤子皮秒光纤激光脉冲重复频率的方法。运用该方法，成功地将激光器重复频率由35.2 MHz降低到了1.77 MHz，且脉冲时频特性保持不变。提出了一种基于级间FBG陷波滤波的抑制皮秒脉冲光纤放大中光谱展宽的方法。通过简单地使用级间陷波滤波器，既可窄化第一级光纤放大器后的输出脉冲谱宽，允许采用第二级光纤放大器进一步提升脉冲能量，而且，还可将脉冲重塑为近高斯形，利用高斯脉冲光谱展宽斜率小的特点，允许第二级光纤放大器将脉冲能量提升得更高。利用该方法，在RMS（均方值）谱宽保持0.4 nm以内的前提下，10 ps脉冲经标准单模光纤放大器后，能量可由0.2 nJ可提升到10 nJ以上。     

A microchip-laser-pumped DFB-polymer-dye laser

A miniaturized, high repetition rate, picosecond all solid state photo-induced distributed feedback (DFB) polymer-dye laser is described by applying a passively Q-switched and frequency-doubled Cr⁴⁺:Nd³⁺:YAG-microchip laser (pulse width Δτ=540 ps, repetition rate ν=3 kHz, pump energy E_pump=0.15 μJ) as a pump source. A poly-methylmethacrylate film doped with rhodamine B dye serves as active medium. The DFB-laser pulses are temporally and spectrally characterized, and the stability of the thin polymer/dye film at high repetition rates is analyzed. The shortest DFB-laser pulses obtained have a duration of 11 ps. After the emission of 350000 pulses the intensity of the DFB-laser output has decreased by a factor of two and the pulse duration has increased by a factor of 1.2. For single DFB-laser pulses of 20-ps duration the spectral bandwidth is measured to be Δλ=0.03 nm, which is only 0.005 nm above the calculated Fourier limit assuming a Gaussian profile for the temporal shape of the pulses. Coarse wavelength tuning of the DFB laser between 590 and 619 nm is done by turning the prism. Additionally, a fine tuning of the DFB-polymer-laser wavelength is achieved by changing the temperature of the polymer/dye layer (=-0.05 nm/°C) in the range from 20 to 40 °C. Received: 1 March 2001 / Revised version: 23 May 2001 / Published online: 18 July 2001     

Sub-picosecond pulses at 100 W average power from a Yb:YLF chirped-pulse amplification system

We present a high-repetition-frequency, diode-pumped, and chirped-pulse amplification system operating at 106 W average output power with excellent beam quality (M(2)=1.3), based on cryogenically cooled Yb:YLF. 1 nJ seed pulses, derived from a mode-locked Ti:sapphire laser, are first amplified to 1 mJ pulse energy at 10 kHz repetition frequency in a regenerative amplifier. The second-stage, multipass amplifier increases the pulse energy to 10.6 mJ, resulting in a spectral width of 2.2 nm. The pulses are compressed to 865 fs in duration, which is 1.26 times the transform limit.     

Mode-locked diode-pumped vanadate lasers operated with PbS quantum dots

The use of glasses doped with PbS nanocrystals as intracavity saturable absorbers for passive Q-switching and mode locking of c-cut Nd:Gd_0.7Y_0.3VO₄, Nd:YVO₄, and Nd:GdVO₄ lasers is investigated. Q-switching yields pulses as short as 35 ns with an average output power of 435 mW at a repetition rate of 6–12 kHz at a pump power of 5–6 W. Mode locking through a combination of PbS nanocrystals and a Kerr lens results in 1.4 ps long pulses with an average output power of 255 mW at a repetition rate of 100 MHz.     

Q-switched and mode-locked diode-pumped Nd:YVO4 laser with an intracavity composite semiconductor saturable absorber

We have demonstrated a passively Q-switched and mode-locked Nd:YVO₄ laser with an intracavity composite semiconductor saturable absorber (ICSSA). Stable Q-switched and mode-locked pulses with Q-switched envelope pulse duration of 180 ns and pulse repetition rate of 72 KHz have been obtained. The maximum average output power was 1.45 W at 8 W incident pump power. The repetition rate of the mode-locked pulses inside the Q-switched envelope was 154 MHz. Experimental results revealed that this ICSSA was suitable for Q-switched and mode-locked solid-state lasers.     

Intense few-cycle laser pulses from self-compression in a self-guiding filament

Sub-10-fs-pulses are generated by self-compression in a noble gas filament. Using input pulses from a Ti:sapphire amplifier system with an energy of about 1.5 mJ at a repetition rate of 3 kHz and a pulse duration of 30 fs self-compressed sub-10-fs pulses with energies of about 0.3 mJ have been generated. These pulses are characterized with spectral phase interferometry for direct electrical-field reconstruction (SPIDER). Depending on the laser parameters, we observe a significant change in the chirp of the white-light. The spectral distribution of the outcoming beam profile is measured to distinguish the white-light core from the surrounding halo.     

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.     

Nd:glass diode-pumped regenerative amplifier,multimillijoule short-pulse chirped-pulse-amplifier laser

We have built a diode-pumped Nd:glass regenerative amplifier that is able to produce energies up to 20 mJ within a 470-fs pulse duration at a 1-Hz repetition rate. We obtained this amplifier by using specific intracavity components such as a phase mirror and a birefringent filter to generate a large spatial mode and a large spectral width.     

A high spectral brightness Fourier-transform limited nanosecond Yb-doped fiber amplifier

In this paper, we present a frequency-doubled pulsed Yb-doped fiber amplifier exhibiting Fourier-transform limited 10-ns pulses at a repetition rate of up to 5 kHz. The amplifier is seeded by an external cavity diode laser whose output is chopped into light pulses of 10- to 1200-ns duration. The first stage is operated with a single-mode fiber, while the other two stages employ multi-mode double clad fibers. Output energies of up to 516 μJ per pulse have been recorded. The output power is limited by the onset of stimulated Brillouin scattering. As an example of the possible applications, we demonstrate the temperature measurement of water by Brillouin scattering employing the frequency-doubled radiation from the amplifier.     

300 kHz femtosecond Yb:KGW regenerative amplifier using an acousto–optic Q-switch

We report a diode-pumped high-repetition-rate chirped-pulse Yb:KGW regenerative amplifier delivering tens of microjoules pulse energy at repetition rates of up to 300 kHz. High repetition rates are obtained by using an acousto-optic modulator as switching element in the regenerative amplifier cavity. The output pulses were compressed down to 600 fs pulse duration. Even shorter pulses in the 100 fs range are obtained using an amplifier configuration without chirped pulse amplification. PACS 42.55.Xi; 42.60.Da; 42.65 Re     

Generation of a 64-GHz, 3.3-ps transform-limited pulse train from a fiber laser employing higher-order frequency-modulated mode locking

We demonstrate the generation of optical pulses at a repetition rate of 64 GHz directly from a frequency-modulated (FM) mode-locked fiber laser. This is achieved by phase modulation at 16 GHz and by initiating of higher-order FM mode locking by use of an intracavity Fabry-Perot filter with a free spectral range of 64 GHz. This process yielded transform-limited pulses with a width of 3.3 ps. We investigated the operating characteristics of the laser and compared them with the characteristics that were predicted theoretically.     

Femtosecond regenerative amplification in Cr:forsterite at 5–10 kHz

We developed a high-power oscillator–regenerative amplifier femtosecond laser system. Based on chromium-doped forsterite. The system is operating near 1.25 μm at a 5–10 kHz repetition rate. Chirped-pulse amplification produced 0.86 W (0.75 W) of average power, or 465 mW (400 mW) after compression at 5 kHz (10 kHz). Nearly bandwidth-limited pulses of duration 135 fs (shortest) and 150 fs (typical) are available with an energy of 93 μJ and 40 μJ at 5 and 10 kHz, respectively. Received: 7 June 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +49-30/63921289, E-mail: petrov@mbi-berlin.de     

Small-scale high-repetition-rate passively Q-switched intracavity OPO at 1.57 μm

A compact small-scale intracavity optical parametric oscillator (IOPO) at 1.57 μm, driven by a diode pumped Nd:YVO₄/Cr:YAG passively Q-switched laser, is experimentally presented. By optimizing the mode matching, low threshold (0.66 W) and high repetition rate (21 kHz) operation of the IOPO has been investigated. At the incident diode pump power of 1.56 W, the miniature (56 mm long) IOPO produces a signal average output power up to 86 mW. Efficient parametric conversion leads to short duration (1.8 ns) pulses and high peak power output (2.3 kW) at 1.57 μm. Moreover, near diffraction limited and Gaussian type signal beam profile is also observed.     

High average power ultra-fast fiber chirped pulse amplification system

We report on a high-gain diode-pumped ytterbium-doped fiber-amplifier system delivering pulse energies in the 100-μJ range at high repetition rates (32 kHz) with nearly-diffraction-limited beam quality (M²∼1.7) at a 1060-nm center wavelength. Femtosecond seed-laser pulses are stretched in a commercially available single-mode fiber and compressed after amplification to subpicosecond pulse duration. In a multimode Yb-doped fiber amplifier we have demonstrated average powers of up to 22 W and single-pulse energies of up to 130 μJ. Received: 16 August 2000 / Revised version: 4 September 2000 / Published online: 8 November 2000     

High-power Kerr-lens mode-locked Yb:YAG thin-disk oscillator in the positive dispersion regime

We demonstrate a self-starting Kerr-lens mode-locked (KLM) Yb:YAG thin-disk oscillator operating in the regime of positive intracavity group-delay dispersion (GDD). It delivers 1.7?ps pulses at an average power of 17?W and a repetition rate of 40?MHz. Dispersive mirrors compress the pulses to a duration of 190?fs (assuming sech² shape; Fourier limit: 150?fs) at an average power level of 11?W. To our knowledge, this is the first KLM thin-disk oscillator with positive GDD. Output powers of up to 30?W were achieved with an increased output coupler transmission and intracavity GDD. We demonstrate increase of the pulse energy with increasing positive intracavity GDD, limited by difficulties in initiating mode-locking.     

Sub-nanosecond single-frequency 10-kHz diode-pumped MOPA laser

A single-axial-mode, passively Q-switched (PQS) diode-pumped Nd:YAG laser, generating a diffraction-limited beam train of ≈40–60 μJ, ∼500-ps pulses with adjustable repetition rate in the range 1–10 kHz, was efficiently amplified by a single side-pumped Nd:YVO₄ bounce amplifier. After double-pass amplification, ≈1-MW pulse peak power with 577-ps duration and 545-μJ energy was achieved, still maintaining diffraction-limited beam performance. The average output power was 5.45 W at 10 kHz, corresponding to 13% extraction efficiency. The high brightness of this laser system seems ideal for nonlinear optics and some particular laser processing applications.     

Intracavity Raman laser generating a third stokes component at 1.5 μm

The lasing properties of an intracavity Nd:KGW Raman laser which converts the multimode radiation of an Nd:KGW laser operating on the ⁴ F _3/2–⁴ I _11/2 transition into the third Stokes component at a wavelength of 1.5 μm are studied. The energy in the third Stokes component is found to increase essentially linearly with the electrical energy delivered to the flashlamp. Lasing at the third Stokes component begins in the central portion of the Nd:KGW crystal and then propagates to its boundaries. Reducing the geometric aperture of the multimode pump beam in the Raman crystal lowers the divergence of the Stokes emission. For a source pump energy of 6 J, the intracavity Raman laser emits 14.7 mJ pulses of duration 3–4 nsec which are safe to the eyes. The divergence of the Raman laser beam at a level of 86% of the total energy is ≈ 9 mrad.