Equipment

1) Main THz experiments

Custom-made setup for THz time-domain spectroscopy

Suitable for measurements of samples in steady state (solids, liquids; temperature range 10 – 900 K; application of high voltage up to 1.5 kV) and for optical pump—THz probe experiments; placed in a vacuum chamber. It can be operated in two modes:

MIRA seed: For the measurement of samples in steady state the experiment is driven with a femtosecond oscillator MIRA seed and uses a recently proposed high-brightness interdigitated semiconductor TeraSED photoswitch as the THz emitter and a 1 mm thick [110]-oriented ZnTe single crystal as an electro-optic (phase-sensitive) sensor.

Peak electric field	0.1 kV/cm
Average power	0.27 mW
Energy per pulse	3.5 pJ
Peak power	0.27 kW
Photons per pulse	~1.4×10¹⁰

ODIN amplifier: For the pump-probe measurement we use femtosecond amplified laser output and the THz pulses are generated via an optical rectification (difference frequency mixing) nonlinear process in a 1 mm thick [110]-oriented ZnTe crystal. An identical ZnTe crystal is used as a sensor for the phase sensitive detection.

Peak electric field	5 kV/cm
Average power	0.7 µW
Energy per pulse	0.7 nJ
Peak power	2.3 kW
Photons per pulse	~7×10¹¹

Fig. 1. Photo of the setup for THz spectroscopy.

Custom-made setup for THz near-field microscopy

The experiment is driven with a femtosecond oscillator VITESSE and uses an interdigitated semiconductor TeraSED photoswitch as the THz emitter and a 1 mm thick [110]-oriented ZnTe single crystal as an electro-optic (phase-sensitive) sensor.

Fig. 2. Photo of the setup for THz near-field microscopy.

2) Laser systems

MIRA seed (Coherent)
ODIN multipass femtosecond amplifier (Quantronix)
VITESSE (Coherent)
TOPAS parametric amplifier

3) Other equipment

Lock-in amplifier Stanford Research 830 DSP
Boxcar averager Stanford 850
Tilted Front Pulse Autocorrelator (TFPA) from Light Conversion
Spectrometer Acton Spectra Pro® 150
Cryostat Oxford Optistat CF from Oxford Instruments, adapted for THz spectroscopy, temperature range 5 – 300 K
High temperature cell adapted for THz spectroscopy from Specac, temperature range 300 – 1000 K

Detailed descriptions of lasers

MIRA seed

Mira is used either for THz experiments with non-amplified pulses or it seed the multipass amplifier (ODIN).

Manufacturer	Coherent Inc.
Mean wavelength	800 nm
Pulse length	50 – 80 fs (adjustable)
Spectral bandwidth	15 – 40 nm
Repetition rate	76 MHz
Energy per pulse	8 nJ
Photons per pulse	~3.5×10¹⁰
Average power	650 mW
Pulse peak power	140 kW

ODIN multipass amplifier

The Odin multipass amplifier is used either in THz experiments with amplified pulses and/or for pumping the optical parametric amplifier (TOPAS).

Manufacturer	Quantronix
Pump laser	527-DP Nd:YLF 12 W
Mean wavelength	800 nm
Pulse length	40 fs (adjustable)
Spectral bandwidth	15 – 30 nm
Repetition rate	1 kHz
Energy per pulse	1 mJ
Photons per pulse	~4×10¹⁵
Average power	1 W
Pulse peak power	25 GW

VITESSE

The Vitesse system is used in conjunction with THz near field microscopy.

Manufacturer	Coherent
Pump laser	Verdi 4.5W
Mean wavelength	800 nm
Spectral bandwidth	10 – 15 nm
Repetition rate	80 MHz
Energy per pulse	11 nJ
Average power	1 W

TOPAS parametric amplifier

The TOPAS parametric amplifier (TOPAS = travelling-wave optical parametric amplifier of super-fluorescence) is typically used for photoexcitation in optical pump – THz probe experiments.

Manufacturer	Light Conversion
Tuning range	240 – 3000 nm
Pulse length	~50 fs
Energy per pulse	1 – 100 µJ (depending on the output wavelength)