Measuring the temporal intensity of ultrashort laser pulses by triple correlation

Received: 13 May 1997/Revised version: 1 August 1997     

Feedback-controlled optimization of amplified femtosecond laser pulses

Received: 17 December 1998     

Emission of laser pulses due to transitions from metastable to metastable levels in strontium vapor

Multi-line laser transitions from one metastable triplet state to another at wavelengths of 2.92, 3.01, 2.69 and 2.60 μm have been obtained through high pulse repetition frequency longitudinal discharge in a mixed gas of strontium vapor and helium buffer gas. The intensity ratio of these laser lines was 5:4:4:1. As far as we know, these laser lines have never been reported except for 3.01 μm. Some mechanisms for forming a population inversion are initially discussed on the basis of analyzing features of corresponding energy-level structure and experimental phenomena. It is reasonable to name this kind of laser as an M–M transition laser according to the feature of the lasing process. Received: 15 October 2002 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +86-0571/8795-1328, E-mail: pbl66@zju.edu.cn     

Pulse shape measurement by a non-collinear third-order correlation technique

A third-order correlator suitable for detailed shape measurements of picosecond laser pulses has been developed. The working principle in both the single shot and the scanning mode is based on detection of the phase-matched difference frequency non-collinear generated signal in a non-linear crystal. This third-order OPA correlator was applied for the characterization of the specifically shaped picosecond laser pulses from the MBI CPA Nd: glass laser system.     

Intracavity Raman conversion for 16-μm Stokes pulse generation in para-hydrogen

16-μm Stokes pulses were directly generated for the first time to our knowledge by an intracavity configuration for the para-hydrogen Raman laser. We have analyzed Stokes field growth using a focused gain model and designed a pump/Stokes cavity to satisfy CO₂ pump power and pulse duration requirements for Raman oscillation. The CO₂ laser oscillation with circular polarization was realized by seeding externally circularly polarized CO₂ radiation. An output energy of 2.4 mJ was obtained with the output coupler of 0.5% transmittance, which indicated that 420 mJ of Stokes pulse energy was stored inside the cavity. This suggests that a much higher energy can be extracted by the optimization of cavity parameters. Received: 18 November 1998 / Published online: 26 May 1999     

Generation of tunable sub-picosecond pulses in the UV with a travelling wave dye laser

Received: 22 June 1998/Revised version: 3 August 1998     

Difference-frequency generation by mixing dual-wavelength pulses emitting from an electronically tuned Ti:sapphire laser

Broadly tunable difference-frequency generation (DFG) in AgGaS₂ was achieved by mixing dual-wavelength oscillating pulses from an electronically tuned Ti:sapphire laser with a two-frequency-driven acousto-optic device. Continuous tuning from 6.5 to 8.5 μm was achieved by simultaneous dual-wavelength-tuned DFG without crystal rotation. In the dual-pulse oscillation, the shorter and longer wavelength pulses were tuned from 700 to 775 nm and from 763 to 880 nm, respectively, while keeping the phase-matching relationship for DFG. When crystal rotation was adopted, however, the tunable output range was extended from 5.3 to 12 μm by tuning the longer wavelength pump pulse, while the shorter wavelength pulse was fixed. Received: 18 November 1998 / Revised version: 5 February 1999 / Published online: 26 May 1999     

High-dynamic-range characterization of ultrashort pulses

Received: 20 June 1997     

Micromirror SLM for femtosecond pulse shaping in the ultraviolet

We present the application of a novel micro mirror array, which is based on a micro electro mechanical system (MEMS), as one- and two-dimensional phase-modulating spatial light modulator (SLM) for femtosecond pulse shaping in the spectral region from the deep-ultraviolet (DUV) to the near-infrared (NIR) (200–900 nm). Using such a high-resolution MEMS-SLM, we demonstrate one-dimensional pulse shaping at 400 nm, including THz-pulse train generation, chirp compensation, and phase wraps. Received: 7 April 2003 / Published online: 2 June 2003 RID="*" ID="*"Corresponding author. Fax: +49-3461/947-202, E-mail: hacker@ioq.uni-jena.de     

Femtosecond ultraviolet pulses generated using noncollinear optical parametric amplification and sum frequency mixing

We demonstrate the generation of ultraviolet 33-fs pulses with a shot-to-shot energy fluctuation of less than 3% using sum frequency mixing of visible pulses of a noncollinear optical parametric amplifier with sub-40-fs pulses of a 1-kHz Ti:sapphire-amplified system. The pulses are transform-limited (ΔνΔτ=0.36) and tunable in the range from 315 nm to 355 nm with energy above 1 μJ (2.6 μJ at 330 nm). Received: 21 July 2000 / Published online: 8 November 2000     

Excimer laser-induced etching of sub-micron surface relief gratings in fused silica using phase grating projection

Phase grating projection using a Schwarzschild objective is presented in conjunction with a process that allows laser-induced etching of transparent materials at the interface of liquids, in order to generate periodical surface relief structures with sub-micron resolution in fused silica. The achieved sinusoidal gratings exhibit a period of 780 nm and a depth of up to 180 nm, having a roughness lower than 5 nm r.m.s. The depth and roughness of the gratings are related to the applied laser fluence and pulse number. In addition to the grating formation, an overall removal of material at higher laser fluences was found. Received: 3 December 2001 / Accepted: 5 December 2001 / Published online: 11 February 2002     

Determination of an optimal five-gas combination in a sealed-off CO<Subscript>2</Subscript> laser

For obtaining the maximal output power, five lasing gas mixtures (CO₂, N₂, He, Xe and H₂) in a sealed-off CO₂ laser are optimized by applying a genetic algorithm and solving CO₂ laser kinetics equations. A comparison of numerical simulations shows that the optimal pressures of CO₂ and N₂ are 1.15 Torr and 7.32 Torr, respectively. Accordingly, the maximum laser power of 124 W is obtained by utilizing the optimal gas combination and an optimized resonator with a length of 1.2 m. Received: 14 August 2002 / Published online: 22 January 2003 The project supported by Zhejiang Provincial Natural Science Foundation of China (No. 602098). RID="*" ID="*"Corresponding author. Fax: +86-571/8832-0369, E-mail: chengch@mail.hz.zj.cn     

Measurement of the temporal coherence of ultrashort harmonic pulses: towards coherent spectroscopy in the extreme ultraviolet

Received: 4 July 1997     

All-reflective interferometric autocorrelator for the measurement of ultra-short optical pulses

We have developed a novel interferometric autocorrelator composed of only reflective elements, which functions as a beam splitter and an optical delay line. Analytical expressions are derived to give second-order autocorrelation functions and deconvolution factors for various conditions. The measurement of femtosecond laser pulses by interferometric autocorrelation is demonstrated in the visible region. The results are compared with those by calculation. Received: 9 December 2002 Revised version: 18 February 2003 / Published online: 5 May 2003 RID="*" ID="*"Present address: Department of Physics, Tokai University, 1117 Kitakaname, Hiratsuka, Kanagawa 259-1207, Japan RID="**" ID="**"Corresponding author. Fax: +81-48/462-4682, E-mail: asuda@postman.riken.go.jp     

SPM-induced spectral compression of picosecond pulses in a single-mode Yb-doped fiber amplifier

In a fiber amplifier, spectral compression due to self-phase modulation is demonstrated for ultrashort pulses. We report the generation of near-transform-limited picosecond pulses with peak powers of several kW at a repetition rate of 74 MHz and diffraction-limited beam quality in a Yb-doped fiber amplifier when seeding with a negative chirped pulse. Received: 17 September 2001 / Revised version: 22 November 2001 / Published online: 17 January 2002     

Generation of femtosecond pulses by two-photon pumping supercontinuum-seeded collinear traveling wave amplification in a dye solution

Visible femtosecond (fs) laser pulses have been obtained in a dye solution with a very simple traveling wave collinear configuration. A femtosecond Ti:sapphire laser (790 nm) pumps the dye solution by two-photon absorption and simultaneously generates supercontinuum, which seeds a light-amplification mechanism. Cross-correlation frequency-resolved optical gating measurements reveal a chirped structure in the dye pulse. The shortest pulse duration achieved is 170 fs and the overall energy efficiency of the process is typically 25%. Received: 22 March 2001 / Revised version: 4 July 2001 / Published online: 19 September 2001     

Remote sensing of the atmosphere using ultrashort laser pulses

Theoretical and experimental studies were performed on the propagation of ultrashort optical terawatt pulses through the atmosphere. Propagation simulations of intense sub-picosecond pulses show that non-linear processes, such as white light generation, can be initiated at a chosen distance by selecting an appropriate group velocity dispersion. With this technique, a white light continuum was generated in the atmosphere whose spectral distribution was characterised in the visible and near infra-red. Applications of this novel light source for atmospheric remote sensing were investigated, combining lidar and time-resolved broadband absorption spectroscopy techniques. Measurements were performed on the oxygen molecule and water vapour. A comparison between the experimental results and the tabulated spectroscopic data led to an excellent correlation with measurements made on water vapour whereas observations on the oxygen showed discrepancy. This study demonstrates that the remote generation of a white light source represents a new way to access the range-resolved multi-trace gas analysis in the atmosphere. Received: 8 December 1999 / Revised version: 18 May 2000 / Published online: 16 August 2000     

Poincaré representation of polarization-shaped femtosecond laser pulses

The usage of Poincaré phase space for the representation of polarization-shaped femtosecond laser pulses is discussed. In these types of light fields the polarization state (i.e. ellipticity and orientation) changes as a function of time within a single laser pulse. Such deliberate variation can be achieved by frequency-domain femtosecond pulse shaping in which two polarization components are manipulated individually. Here it is shown how these light pulses can be represented as temporal trajectories through the ellipticity-orientation (Poincaré) phase space, whereas conventional light (either continuous-wave or pulsed) is determined by only one specific Poincaré location. General properties of parametric Poincaré trajectories are discussed, and their relation to experimentally accessible pulse-manipulation parameters (i.e. amplitudes and phases) determined. Specifically, it is shown how the maximum rate by which a given polarization state can be turned into a different one (at significant intensity levels) is limited by the spectral laser bandwidth. Apart from their direct usage in polarization-shaped pulse representation, Poincaré trajectories also form the basis for intuitive quasi-three-dimensional renderings of the electric field profile. There, the temporal evolution of polarization, intensity, and chirp is directly apparent in a single illustration. Received: 10 December 2002 / Published online: 24 April 2003 RID="*" ID="*"Corresponding author. Fax: +49-931/888-4906, E-mail: brixner@physik.uni-wuerzburg.de     

Tunable picosecond UV source at 10 kHz based on an all-solid-state diode-pumped laser system

4 laser. The amplified pulses were frequency-converted in the blue and in the UV by harmonic generation (doubling and tripling) in two lithium triborate (LBO) crystals. Received: 11 March 1997/Accepted: 24 April 1997