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A study of the electrical properties of ITO layers combined with underlying optical interference layers and their optical properties and surface roughness.

Few-cycle pulse generation based on Ti:sapphire, Cr:forsterite, and Cr:YAG gain media is reviewed. The dynamics of these laser systems is well understood in terms of soliton and dispersion managed soliton formation stabilized by artificial saturable absorber action provided by Kerr-lens modelocking. These systems generate 5-, 14-, and 20-fs pulses with spectral coverages of 600-1150, 1100-1600, and 1200-1500 nm, respectively. The design of dispersion compensating laser optics providing high reflectivity and prismless operation over this bandwidth is discussed. A novel active synchronization scheme based on balanced optical cross correlation, the equivalent to balanced microwave detection, for synchronization of independently mode-locked lasers is introduced. Its use in synchronizing an octave-spanning Ti:sapphire laser and a 30-fs Cr:forsterite laser yields 300 attoseconds timing jitter measured from 10 mHz to 2.3 MHz. The spectral overlap between the two lasers is large enough to enable direct detection of the difference in the carrier-envelope offset frequency between the two lasers. These are the most important steps in the synthesis of single-cycle optical pulses with spectra spanning 600-1600 nm.

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 /spl mu/s, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser.

We generated self-starting sub-10-fs pulses from a Ti:sapphire laser using a combination of a broadband semi- conductor saturable absorber mirror (SESAM), novel double- chirped mirrors, and Kerr-lens modelocking. We present a de- tailed overview of broadband SESAMs used in Ti:sapphire lasers and discuss their design issues. Using such a SESAM to assist the KLM process, we have generated pulses with a duration of only 6: 5f s, the shortest to date directly from the laser. Pulses as short as 13 fs were generated by soliton modelocking alone. Higher-order dispersion compensation was achieved with novel double-chirped mirrors in combina- tion with intracavity prisms.

A double-chirped mirror structure with broadband negative dispersion was realized with semiconductor technology. The necessary high precision of the fabrication was achieved by using special calibration structures. A single reflection on the obtained low-loss mirror produces sufficient negative dispersion for dispersion compensation in a femtosecond laser cavity. In this way we demonstrate 200 fs pulses from a compact Nd:glass laser without any additional dispersion compensation.

For the first time a two-chip wavelength-selective InGaAs-InP Fabry-Perot p-i-n receiver for dense wavelength-division-multiplexed systems is presented. This concept allows one to easily place the p-i-n diode outside the resonant cavity. A cavity length of more than 30 /spl mu/m is applied to obtain a small optical bandwidth of the receiver. The device can be combined with micromachined actuators for wavelength tuning. First measurements of the receiver showed a full-width at half-maximum bandwidth of 0.6 nm and a finesse of 53. The overall losses of the receiver including fiber-to-chip coupling losses are 6.6 dB.

X-ray fluorescence spectrometry with total reflection conditions is applied in the qualitative and quantitative determination of impurities in thin layers of Ti, TiO2, and HfO2 prepared by evaporation and of SiO2, TiO2, and Ta2O5 prepared by ion beam sputtering. The same method is used to examine stainless steel discs, which have to be used as reference materials

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.

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.

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.

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.

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.

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.  1997 Optical Society of America Short-pulse generation has advanced to a degree where the bandwidth of standard Bragg mirrors composed of SiO2yTiO2 layer pairs limits the pulse width of ultrashort pulsed lasers. Chirped mirrors 1 overcome the bandwidth limitation and provide simultaneously a means for compensation of the group-delay dispersion in the laser. However, so far the chirped-mirror design has been done by computer optimization, 1 because a simple chirping of the center wavelength of the Bragg mirror is not enough. 2 Chirping would introduce oscillations in the group delay for longer wavelengths, which penetrate deeper into the mirror. The oscillations are due to an effective Gire‐Tournois interferometer. The interferometer is created by partial reflection from the front section of the mirror, which acts as a transmission grating, and the reflection at the back of the mirror, which acts as a Bragg reflector. We present an analytic design for chirped mirrors based on coupled-mode and transmission-line theory. The cause of the oscillations in the group-delay dispersion is identified as an impedance-matching problem. We solve this problem by slowly tapering the impedance, which is shown to be equivalent to a chirp in the thickness of the high-index layer in addition to the chirp of the center wavelength of the Bragg mirror.

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.

An octave spanning prismless Ti:sapphire laser is demonstrated. The octave is reached at 20 dB below the average power level. A highly stable carrier-envelope beat note with 30 dB signal to noise in a 100 kHz detection bandwidth is observed and locked to microwave synthesizer.

We present the design for an ultra-broadband beam splitter from 600 to 1500 nm for femtosecond laser applications. The splitter shows the same dispersion in reflection and transmission equal to a thin fused silica plate.

Summary form only given. We have generated the shortest pulses to date directly from a KLM Ti:sapphire laser, with a 5.5 fs pulsewidth at 100 MHz repetition rate. This corresponds to a spectral width extending from 650 to over 1000 nm. The demonstrated spectrum at high repetition rates obtained from this source enables many applications including broadband and multiwavelength femtosecond spectroscopy, spread spectrum and WDM systems applications, as well as optical coherence tomography with sub-2 micron resolution.

Cr3+:LiCAF is a very promising material for compact femtosecond laser sources because of its low quantum defect, a broadband emission range around 800 nm, and an absorption band in a spectral range where high-brightness laser diodes are available. For applications such as seeding, ultra high resolution optical coherence tomography, or metrology a compact replacement for the Ti:sapphire oscillator would be highly desirable. Although the gain bandwidth of Cr3+:LiCAF supports pulses substantially shorter than 10 fs, the shortest pulse width so far demonstrated from a mode-locked Cr3+:LiCAF -Laser is 19 fs [2]. It has been suggested that higher order dispersion and the strong Raman-effect occurring in Colquiirite crystals [2, 3, 4] which leads to a red shift of the spectrum each pass through the gain medium is limiting short pulse generation.

We have fabricated a two-chip wavelength selective InGaAs-InP Fabry-Perot PIN receiver for dense wavelength division multiplex systems. The receiver can be combined with micromachined actuators for wavelength tuning. We have presented an InGaAs-InP wavelength selective PIN receiver for dense WDM systems. The structure can be integrated with micromachined actuators to built tunable wavelength selective receivers. Our on-going work is dealing with the fabrication and optimization of the PIN receivers which is presented here. They will be combined with our micromachined actuators to become tunable wavelength selective PIN receivers for dense WDM applications.

External compression of ultrashort pulses from Ti:sapphire lasers has led to pulses as short as 4.5 fs at a center wavelength of 800 nm, which is less than two optical cycles. It is a challenge to generate such short pulses at high repetition rates directly from the Ti:sapphire laser which is the topic of this contribution. The main limitation in achieving this goal is the design and fabrication of the intracavity optics that provides the proper dispersion compensation and the bandwidth for such short pulses. The pulsewidth and spectral shape of pulses generated directly from the laser depends much more strongly on the quality of the dispersion compensation than for pulses obtained by external compression.

Pulses shorter than two optical cycles at 90 MHz repetition rate and 200 mW average power are demonstrated using a Kerr-lens modelocked Ti:sapphire laser with improved dispersion compensation. The pulse formation is explained by dispersion-managed soliton generation. An initial application of this source to ultra high resolution optical coherence tomography is demonstrated.

Summary form only given. The generation of spectra extending over one octave directly from a laser oscillator is challenging in many aspects. First of all, the limited gain bandwidth of the laser material, about 200 nm in the case of Ti:sapphire, has to be overcome by nonlinear spectral broadening (SB) via self phase modulation (SPM). The amount of SPM and hence the SB per roundtrip is determined by the available intracavity pulse energy, which is limited by optimum Kerr lens mode-locking (KLM) action. Second, one has to provide a high mirror reflectivity and well controlled dispersion properties over the whole desired spectral range. Recent efforts in this field provided pulses in the two-cycle regime with bandwidths below one octave. In our work we refined the intracavity approach by adding a second intracavity focus. Together with specially designed double-chirped mirror pairs, we obtained the broadest spectrum ever generated directly by a laser and successfully recompressed the pulses to 5 fs.

We demonstrate Ti:sapphire laser pulses of unprecedented spectral width, covering an optical octave without external continuum generation. The pulse spectrum spans more than 170 THz and supports bandwidth-limited two-cycle pulses. Assuming a sech2 pulse, the autocorrelation corresponds to a 4.8-fs pulse duration. The average power is 300 mW at a repetition rate of 100 MHz. The key features of the cavity are: dispersion compensation with broadband double-chirped mirrors combined with a prism pair, a broadband semiconductor saturable absorber mirror (SESAM) to assist Kerr-lens modelocking, and an output coupling mirror specifically designed to broaden the pulse spectrum.

Summary form only given. Sub-10-fs pulse generation via external compression as well as direct generation from Kerr-lens mode-locked lasers relies on chirped mirrors for dispersion compensation. Pulses shorter than two optical cycles have been generated directly from the laser using double-chirped mirrors (DCMs) and CaF/sub 2/ prisms for precise control of the intracavity group delay dispersion (GDD) over almost 400-nm bandwidth. To approach the generation of single cycle pulses laser optics with a bandwidth of more than one octave are necessary. There have been several proposals to increase the bandwidth by mutual compensation of GDD oscillations using pure computer optimization. So far this resulted in a low reflectivity of less than 95% over almost half of the bandwidth considered. An analytic design of double chirped mirror (DCM) pairs covering one octave of bandwidth with reflectivity greater than 95.5% and improved dispersion characteristics is presented.

We present a novel design approach for chirped mirror dispersion compensation, suitable for octave-filling spectra with strongly reduced dispersion oscillations. We present measurements on a mode-locked Ti:sapphire laser and explore the limits using full amplitude and phase characterization of our ultrabroadband pulses.

Femtosecond and picosecond pulses can find many applications if they can be produced with laser sources that are not only powerful and efficient but also compact and reliable. In continuous wave operation, diode pumping of solid-state lasers has allowed for a rapid progress towards powerful, compact and reliable sources, while the often used technique of Kerr lens modelocking for pulsed operation tends to be in conflict with requirements for diode-pumpable high power designs. Passive modelocking with semiconductor saturable absorber mirrors solves this problem as it relaxes the restrictions on the cavity design. We report on our recent achievements in this field. In particular we present a novel semiconductor device for dispersion compensation and various improved diode-pumped passively modelocked lasers. Also we show which laser parameters determine the stability of a passively modelocked lasers against Q-switching instabilities.

We have fabricated InGaAs/InP PIN diodes with a coplanar waveguide design. The diodes have been integrated in a two- chip wavelength-selective Fabry-Perot filter for the use as wavelength-selective PIN receivers for dense wavelength division multiplex systems.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Ion beam sputtered SiO 2 and TiO 2 optical thin films are investigated. The optical properties absorption, light scattering and refractive index and the mechanical properties thickness, density and stress are studied directly after deposition and the posttreatment by isochromal annealing up to 300 degree(s)C. Absorption losses of SiO 2 single layers decrease under annealing. The corresponding extinction is reduced below 1 X 10 -6 at 514 nm. The dynamics of this process is investigated. The density which is higher than bulk density decreases, while the thickness increases. TiO 2 single layers show a more complex behavior under postannealing. At higher temperatures this behavior is dominated by crystallite growth in anatase and rutile modification. Compressive stress is reduced. The single layer results of both materials are compared with those of double layers and Fabry Perot multilayers. Differences in absorption are discussed. In double layer systems, lowest bulk extinction of TiO 2 is estimated with 1.5 X 10 -5 at 514 nm. An irreversible peak shift of Fabry Perot filters after annealing comes from changes in thickness and refractive index. The overall performance of multilayer systems can be improved by an adapted annealing procedure.

Absorption losses in ion beam sputtered films of SiO2 and TiO2 were examined. Two different processes contribute to the absorption of the films. The first process is the incorporation of impurities from the target itself, the ion source and the target surroundings into the films. The second is the damage of the films if a too large amount of energy is transferred to them by the sputtered and reflected particles. Impurity incorporation was minimized by a special coating chamber configuration and the use of electron cyclotron resonance ion and electron sources. The contaminations are examined by Secondary Ion Mass Spectrometry, using ion implantations for quantification. The influence of the main impurity parts on absorption is determined by controlled addition of impurities to the films. Experimental results show a large influence of the sputter gas, the reactive gas flow and the kind of target on absorption. Numerical sputter simulations revealed the correlation of these results with energy transport to the films. Reducing energy deposition in the films reduces their absorption. Low absorption in ion beam sputtering can only be achieved using metal targets.

In this presentation the design concept of an instrument for measuring total integrated scattering with a resolution limit of 0.1 ppm will be described. Furthermore the result of a theoretical model will be given which includes the scattering contributions from the front and the back surface of a transparent substrate. With the result obtained, surface roughness and power spectral density functions of the individual substrate surfaces can be calculated from scatter measurements. The improved measurement facility of the instrument in conjunction with the developed theoretical model allows surface characterization of transparent substrates in case of negligible volume scattering of the bulk material. Measurement results will be presented verifying the results of the model and showing the instrument's ability to characterize polishing quality of transparent substrates. Scatter losses as low as 0.6 ppm corresponding to 1 angstrom rms surface roughness have been determined measuring a `superpolished' transparent fused quartz substrate.

The absorption in Ion Beam Sputtered laser mirrors was examined. It is known that impurities influences the absorption of optical films. Therefore the impurity content of the sputtered films has been investigated using total reflection X-ray fluorescence analysis (TRFA). Impurity analysis revealed stainless steel components (iron, chromium, nickel) to be an important part of the impurities, but also material from the preceding sputter run was detected. The absorption measurement showed that besides the stainless steel components the cosputtered material leads to an enlarged absorption. These absorptions are causing mirrors deformations in a high power argon laser.

Cross-sections of dielectrical laser mirrors are examined by Transmission Electron Microscopy (TEM). The TEM picture shows the whole layer structure which offers the possibility to observe the development of interface roughness from the substrate up to the top layer. The TEM pictures reveal the great difference between the interface roughness of evaporated and ion beam sputtered layers. Using computer image processing techniques the increasing roughness within the evaporated layer system has been measured. Furthermore the correlation lengths of the roughness has been determined in this way. The knowledge of these two parameters over the entire system enables the calculation of scatter losses for the system.

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.

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.

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.

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.

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.

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.

Ion Beam Sputter Deposition (IBSD) was proven to be a useful technique for producing high performance optical coatings. However, compared to other deposition techniques, several problems remain to be solved, such as low deposition rates, small areas with homogeneous deposition rate and the problem of contamination. In the work described here, a cubic vacuum chamber has been equipped with a commercially available ion beam source, a triple stage target holder and a rotating substrate holder. The primary interest was to get a reasonable deposition rate over a sufficiently large area. Single layers of SiO2, Ta205 and TiO2 and multilayers of Si02/Ta205 were produced. Contaminants in the films were analyzed by various techniques mainly by Total-Reflection X-ray Fluorescence (TXRF). Optical properties of the coatings were investigated to study the influence of the contaminants on the performance of the optical coatings. The optical properties were characterized by the refractive index, the absorption coefficient and the scattering behaviour. Scattering losses were measured by means of Total Integrated Scattering (TIS) and Angle Resolved Scattering (ARS). The damage threshold against high-power laser pulses of 1.06 pm was determined.

The quality of resonator mirrors still is a limiting factor of beam quality and output power for high power argon ion lasers. To compare the different coating and substrate materials and deposition methods it is necessary to measure the absorption of the mirrors. The absorption is of order 10- 4 . We use the high intracavity power of an argon ion laser to measure this absorption. An external interferometer records the mirror deformation while the 1aser is in operation. The laser mirror itself performs as a shearing interferometer. From the recorded interferogram we calculate the temperature distribution of the laser mirror and deduct its absorption.

Sub-10 fs pulse generation via external compression as well as direct generation from Kerr-Lens mode-locked laser oscillators relies on chirped mirrors for dispersion compensation. Pulses shorter than two optical cycles have been generated directly from the laser using double chirped mirror (DCMs) for precise control of the intracavity group delay dispersion (GDD) over almost 400 nm bandwidth. To approach the generation of single cycle pulses laser optics with a bandwidth of more than one octave are necessary. In this paper, an analytic design of double-chirped mirror (DCM) pairs covering one octave of bandwidth with reflectivities greater than 99.5% and improved dispersion characteristics is presented. Results achieved with fabricated mirror pairs are shown.

We present a unique combination of an improved octave-spanning laser oscillator and prism-based pulse shaper allowing for the generation of various pulse shapes and sequences for coherent control experiments.

Well-characterized pulses in the two-optical-cycle regime are demonstrated using a Kerr-lens modelocked (KLM) Ti:sapphire laser and phase-sensitive diagnostics. The oscillator employs double-chirped mirrors (DCMs) for dispersion compensation, spectral shaping via wavelength-dependent output coupling, and a semiconductor saturable absorber mirror (SESAM) for reliable operation at up to 300 mW output power and with a repetition rate of ∼90 MHz.In the discussion of the experimental results we emphasize how spectral shaping can be used most efficiently in the generation of the shortest possible pulse supported by the Ti:sapphire gain bandwidth.

We present a theory for the analytical design of double-chirped mirrors (DCMs) with a controlled dispersion characteristic. Theoretical designs are derived from an analytical chirp law. These are then used as excellent starting designs for later computer refinement. The design procedure presented here results in improved broadband DCM designs for higher order dispersion compensation in sub-10-fs Ti:sapphire lasers.