Ultrabroadband beam splitter with matched group-delay dispersion.

We present a general design strategy for a broadband thin-film beam splitter with matched group-delay dispersion. By taking the substrate dispersion into account in the coating design, any combination of input and output can show the same dispersion for transmission and reflection. As a specific implementation, an ultrabroadband 50:50 beam splitter from 600 to 1500 nm for femtosecond laser applications was designed, fabricated, and characterized.

Generation of 150-nJ pulses from a multiple-pass cavity Kerr-lens mode-locked Ti:Al2O3 oscillator.

A high-pulse-energy, prismless, Kerr-lens mode-locked, extended cavity Ti:sapphire laser is demonstrated with double-chirped mirrors and a multiple-pass cavity. The laser operates at 5.85-MHz repetition rate and generates pulse energies as high as 150 nJ with 43-fs pulse duration, corresponding to peak powers of 3.5 MW directly from the laser.

Generation of 20-fs pulses by a prismless Cr(4+):YAG laser.

Ultrafast optical pulses shorter than 20 fs with 400-mW average power at a 110-MHz repetition rate have been generated by a Cr(4+):YAG laser with only double-chirped mirrors for dispersion compensation. The corresponding pulse spectrum has a peak intensity at 1450 nm and extends from 1310 to 1500 nm full width at half-maximum (FWHM). These pulses, which are believed to be the shortest generated to date from a Cr(4+):YAG laser, are only four optical cycles within the FWHM intensity width.

Generation of sub-10-fs pulses from a Kerr-lens mode-locked Cr(3+):LiCAF laser oscillator by use of third-order dispersion-compensating double-chirped mirrors.

Pulses as short as 9 fs at 220-mW average power and a 97-MHz repetition rate are generated from a cw Ti:sapphire-pumped Kerr-lens mode-locked Cr(3+)LiCAF laser oscillator employing broadband double-chirped mirrors for second- and third-order dispersion compensation. Fine adjustment of dispersion is accomplished with a fused-silica prism pair. The result demonstrates that Raman-induced self-frequency shifting of the pulse does not limit sub-10-fs pulse generation from colquiriite crystals.

All-solid-state Cr:forsterite laser generating 14-fs pulses at 1.3 mum.

We report the generation of 14-fs pulses at 1.3mum with 80-mW average power at 100-MHz repetition rate by an all-solid-state Kerr-lens mode-locked Cr:forsterite laser. The laser spectrum covers wavelengths of 1230-1580 nm, with a FWHM of 250 nm. Since 1.3-mum wavelengths are close to the zero dispersion wavelength of Cr:forsterite, higher-order dispersion is the main factor limiting pulse durations. We use specially designed and fabricated double-chirped mirrors in combination with high-index PBH71 prisms to compensate for the intracavity dispersion over almost 300 nm.

Generation of 5-fs pulses and octave-spanning spectra directly from a Ti:sapphire laser.

Spectra extending from 600 to 1200 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser producing 5-fs pulses. Specially designed double-chirped mirror pairs provide broadband controlled dispersion, and a second intracavity focus in a glass plate provides additional spectral broadening. These spectra are to our knowledge the broadest ever generated directly from a laser oscillator.

Pulse compression over a 170-THz bandwidth in the visible by use of only chirped mirrors.

We report on double-chirped mirrors with custom-tailored dispersion characteristics over a bandwidth of 170 THz in the visible. The mirrors are used in a prismless compressor for a noncollinear optical parametric amplifier in the visible. The compressed pulses, characterized for the what is believed to be first time by use of the spectral phase interferometry for direct electric field reconstruction technique, display a nearly flat phase from 510 to 710 nm and have a duration of 5.7 fs.

Sub-two-cycle pulses from a Kerr-lens mode-locked Ti:sapphire laser.

Pulses shorter than two optical cycles with bandwidths in excess of 400 nm have been generated from a Kerr-lens mode-locked Ti:sapphire laser with a repetition rate of 90 MHz and an average power of 200 mW. Low-dispersion prisms and double-chirped mirrors provide broadband controlled dispersion and high reflectivity. These pulse durations are to our knowledge the shortest ever generated directly from a laser oscillator.

Semiconductor saturable-absorber mirror assisted Kerr-lens mode-locked Ti:sapphire laser producing pulses in the two-cycle regime.

Pulses of sub-6-fs duration have been obtained from a Kerr-lens mode-locked Ti:sapphire laser at a repetition rate of 100 MHz and an average power of 300 mW. Fitting an ideal sech(2) to the autocorrelation data yields a 4.8-fs pulse duration, whereas reconstruction of the pulse amplitude profile gives 5.8 fs. The pulse spectrum covers wavelengths from above 950 nm to below 630 nm, extending into the yellow beyond the gain bandwidth of Ti:sapphire. This improvement in bandwidth has been made possible by three key ingredients: carefully designed spectral shaping of the output coupling, better suppression of the dispersion oscillation of the double-chirped mirrors, and a novel broadband semiconductor saturable-absorber mirror.

Self-starting 6.5-fs pulses from a Ti:sapphire laser.

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens mode-locked Ti:sapphire laser with 200-mW average output power at a pulse repetition rate of ~86 M Hz. This is to our knowledge the shortest pulse ever generated directly from a laser. For dispersion compensation we used a prism pair in combination with double-chirped mirrors, which balances the higher-order dispersion of the prism pair and therefore flattens the average total group-delay dispersion in the laser cavity. For self-starting mode locking we used a broadband semiconductor saturable-absorber mirror.

Design and fabrication of double-chirped mirrors.

We present an analytic design method for the reproducible fabrication of double-chirped mirrors to achieve simultaneously a high reflectivity and dispersion compensation over an extended bandwidth compared with those of standard quarter-wave Bragg mirrors. The mirrors are fabricated by ion beam sputtering. Use of these mirrors in a Ti:sapphire laser leads to 6.5-fs pulses directly out of the laser. The method can also be applied to the design of chirped-fiber gratings and general optical filters.

Coatings for optical applications produced by ion beam sputter deposition.

Ion beam sputter deposition (IBSD) is a useful technique for producing high performance optical coatings. It is possible with relatively simple methods to get a reasonable deposition rate over a sufficiently large area. However, thin films produced with this coating method had a relatively high amount of contaminants. The contaminants were analyzed by various techniques mainly by total reflection x-ray fluorescence. The influence of the contaminants on the performance of the optical coatings proved to be surprisingly low. Optical properties were investigated, mainly the refractive index, the absorption coefficient at 0.514 mum, the scattering behavior, and the damage threshold against high-power laser pulses at 1.06 mum.