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250 kHz LASER SOURCE and HIGH POWER OSCILLATOR


The source is a double laser system from Coherent Inc.
A high power (18 Watt) CW solid state laser (Verdi 18), pumps either an oscillator (Mira Seed) and an amplifier (RegA), or a high power oscillator (Mira HP).



Laboratory sketch: 1=Verdi 18, 2=Mira HP, 3=Mira Seed, 4=RegA, 5=stretcher-compressor, 6=pulse picker, 7=OPA, 8=DFG, 9=TR optical spectroscopy, 10= Spin resolved ARPES, 11= ARPES

1. 250 kHz LASER SOURCE
It consists of a Ti:SA oscillator (Mira Seed) and a high repetition rate Ti:SA amplifier (RegA). The oscillator is synchronizable to an external RF signal.
The oscillator output consists of pulses with the following specifications:
λ = 800 nm (tunable in the range 780-840 nm)
bandwidth = 40 nm
average power = 800 mW
τ = 50 fs
Repetition rate 80 MHz

After the amplification, the pulses have the following characteristics:
λ = 800 nm
bandwidth = 26 nm
average power = 1.1 W
τ = 50 fs
Repetition rate = 250 kHz (the repetition rate is tunable from 10 kHz to 300 kHz)

2. OPTICAL PARAMETRIC AMPLIFIER
It is possible to tune the laser output in the infrared by means of an OPA.
Tuning range: 1200-2500 nm
Pulse Energy: <1 μJ
τ < 60 fs

3. DIFFERENCE FREQUENCY GENERATOR
To push the wavelengths further in the infrared, the output of the OPA seeds a DFG.
Tuning range: 2,5-10,0 μm
Pulse Energy: <10 nJ
τ < 100 fs

4. TIME RESOLVED OPTICAL SPECTROSCOPY
The pump-probe scheme uses 50 mW of the RegA output (λ = 800 nm) as pump beam, while the OPA output is used as probe beam.
The time delay is controlled by a fast-moving mechanical delay line (maximum frequency 20 Hz on a 50 ps delay range), monitored in real-time, allowing a highly reliable acquisition of the pump-probe dynamics.
The pump beam is mechanically chopped at high frequency (maximum frequency 125 kHz, half of the laser repetition rate), enabling a lock-in amplification of the pump-probe signal with a 10-6 signal-to-noise ratio in few minutes on the full delay range.
The pump-probe signal can be analyzed either using the full OPA-bandwidth for best time-resolution (60 fs) or with an automated monochromator, to achieve a better wavelength resolution (< 1 nm).

The sample is placed in an open-cycle cryostat to perform temperature-dependent measurements in the range from 420 K down to 6 K. The cryostat is built and mounted inside a 1 T magnet, allowing a magnetic field to be applied on the sample.

5. FOURTH HARMONIC GENERATION
An optical set up has been realized to generate the 4th harmonic of the laser, λ = 200 nm, in phase matching conditions, to serve an experimental chamber for spin resolved ARPES (Angle Resolved PhotoEmissionSpectroscopy) measurements.

6. HIGH POWER OSCILLATOR
The Verdi 18 can also pump a widely tunable Ti:SA oscillator (Mira HP), also synchronizable to an external RF signal.
The oscillator output consists of pulses with the following specifications:
λ = 800 nm (tunable in the range 700-1000 nm)
bandwidth = 12 nm (@ 800 nm)
average power = 4.5 W (@ 800 nm)
τ = 150 fs
Repetition rate 80 MHz

7. PULSE PICKER
This optical apparatus allows to tune the repetition rate of Mira HP in the range 1-10 MHZ, halving the pulse energy.

8. FOURTH HARMONIC GENERATION
Another optical set up has been realized to generate the 4th harmonic of the oscillator, getting pulses at 205 < λ < 210 nm, in quasi phase matching conditions, to serve another experimental chamber for ARPES measurements.

9. TIME RESOLVED XMCD
The aims of the time resolved spectroscopic chamber installed on the BACH beamline is to carry out time resolved absorption experiments in the soft x-ray range.
The synchrotron x-ray pulses and the laser pulses are synchronized by means of a “phase shifter divider” (or synchronization unit). (ref. Paolo Sigalotti, Elettra)
The synchronization unit provides 83.3 MHz reference signals that are used to synchronize the laser pulse and the detector electronics, in order to maintain phase relationship and timing information.
The detection setup consists of an ultra fast high time resolution microchannel plate (MCP) detector built by the Hamamatsu company. The measured time resolution of the detector is 500 ps with an applied voltage of 1600 Volts. The reference number of the detector is F4655-13. The detector is mounted in an ultra high vacuum (UHV) chamber equipped with a standard sample mounting and a normal total electron yield (TEY) detection mode setup. The availability of permanent magnet in the chamber provides the opportunity to perform X-ray circular and linear magnetic dichroism.
The detector electronics pre-amplifies and discriminates the detected events and stores each acquired event according to the arrival time respect to a reference “0” time (ref. Luigi Stebel, Elettra).

10. Time Resolved ARPES
See Linked Page 

For further informations You can contact Federico Cilento
Ultima modifica il Giovedì, 29 Agosto 2013 11:27