Current research projects

Diode pumped femtosecond sources

Even though titanium doped sapphire proved to be an excellent laser crystal for femtosecond sources, a quest continues for new materials that would offer, among other properties, a possibility of direct diode pumping. Among them, ytterbium doped crystals, glasses and ceramics have attracted much attention in the recent years with their absorption band overlapping the band of 980 nm laser diodes developed for telecom applications (EDFA pumping).

We are currently developing prototype femtosecond oscillators with an integrated pump, operating near 1030 nm with an optional upcovertion to the green. We use Yb:KYW crystals grown, oriented and cut in the Military Institute of Technology, Warsaw (WAT) as well as from commercial sources.

We have built a standard z-fold cavity laser with 80 MHz rep rate (planned as a seed for high power fiber amplifier) and the first 1 GHz Yb:KYW laser for applications in precision metrology.

Femtosecond ytterbium fiber laser

In recent years many of the formerly free space optical set-ups have been implemented in the fiber technology due to its various advantages. In particular, research groups in the word develop fiber lasers that demonstrate excellent stability, compact size and freedom from misalignment. Since most of the projects in our laboratory concern ultrafast processes we aim to construct a femtosecond fiber oscillator equivalent to the freespace lasers used in our lab. This laser is based on ytterbium (Yb) doped fiber, pumped by single mode laser diode at 980 nm and emitting at around 1030 nm. The laser is already working in CW and it is waiting for modelocking.

Time Resolved Fluorescence setup

With the appearance of lasers delivering pulses as short as several femtoseconds in the mid 80's the holy grail of chemistry – to observe a chemical reaction in real time – was just round the corner. A milestone in that field was met when Ahmed Zewail showed how the probability of dissociation of NaI molecule changes during the period of molecules stretching vibration. These and similar experiments gave birth to new field called femtochemistry that uses ultrashort pulses in a variety of different ways to observe chemically interesting dynamics.

To be able to follow the world trends we constructed a state of the art setup in which we observe fluorescence emitted by molecules exited by a short pulse. In our setup we can follow spectral changes of fluorescence with 150 fs time resolution while registering full width spectra.

The setup is powered by two NOPA amplifiers delivering 40 to 70 fs pulses. The specimen emission is collected by low time dispersion all- reflective objective in Schwarzchild configuration. Both fluorescence and the second short gating pulse are crossed in a BBO crystal where upconverion takes place. The ability to quickly rotate this BBO crystal combined with imaging spectrograph allows us to register full fluorescence spectrum at each time step.

Terrawatt optical parametric chirped pulse amplifier

Since the first demonstration of parametric amplification of chirped femtosecond pulses in ß-barium borate (BBO) Optical Parametric Chirped Pulse Amplifier (OPCPA) has become an increasingly popular tool used to generate high peak power pulses including pulses with sub-PW power levels. There are several advantages of optical parametric amplifiers in high power systems that make them more attractive than standard laser amplifiers: very broadband operation in a noncollinear configuration (over 200 nm @800 nm for BBO crystal) essential for short pulse systems, high single pass gain and, finally, no heat accumulation in the gain medium, which enables a straightforward scaling of the system without beam quality deterioration.

In our research we use a new method which is suitable for the power amplifier stage and, in our setup, improves the time overlap by a factor of 3. Together with multi-pass preamplifier parametric preamplifier, it allows the development of a broadband, simple and efficient terawatt level OPCPA system which amplifies short pulses directly from a titanium sapphire oscillator using commercially available ns pump laser.

Infrared time-resolved transient absorption setup

The spectrum of available measurement techniques in spectroscopy constantly increases. The most recent achievements include experiments investigating ultrafast phenomena in matter.

Currently built infrared transient absorption experiment is a technique complementary to our recently developed time-resolved fluorescence spectrometer. The setup involves generating two femtosecond laser pulses: first for excitation of the sample in UV/VIS and second widely tunable (3-11 µm) IR pulse for measurements of IR spectra evolution in time. Both pulses will be derived from a 100 kHz repetition rate amplified Ti:sapphire oscillator by means of parametric processes in nonlinear crystals.

The setup will be used to investigate several phenomena: nonradiative relaxation, inter- or intra-molecular hydrogen transfer, charge transfer, isomerisation and many others.

Optical frequency comb

The invention of frequency comb led to an explosion of activity in many research areas, such as laser stabilization, optical clocks, precision spectroscopy, coherent control of chemical processes and attosecond pulse generation.

In our lab work is underway on a frequency comb system based on gigahertz repetition rate Ti:Sa femtosecond oscillator. Stabilization of carrier-envelope offset is realized by way of self referencing of an octave-spanning spectrum in a novel, low fluctuation collinear interferometer. Babinet-Soleil compensator based, collinear design of f-2f interferometer ensures that both f and 2f components are being subjected to the same drift- and fluctuation-based phase change.

After changing the 'heart' of our setup from previous 80 MHz oscillator, we are focusing on providing a reliable, self-starting modelocking solution with as few movable parts as possible. Our nearest goal is to generate pulses with peak powers sufficient for creating reliable octave-spanning spectra for self-referencing by nonlinear processes in photonic crystal fiber.